Discussion Paper 2 Sloping sites - managing cut and fill May 2012

Transcription

1 Review of Tweed Development Control Plan Section A1 - Residential and Tourist Development Code Part A - Single dwelling houses, alterations and additions Discussion Paper 2 Sloping sites - managing cut and fill May 2012 Bark Architects Sparks Architects

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3 Contents Introduction 4 What issues will the review address? 5 What about the other parts of the plan? 5 What about major subdivision of land? 5 What will happen next? 5 How long is this review likely to take? 5 The Issues 6 Current Statutory Requirements 8 DCP A1 Residential & Tourist Development Code 8 DCP A5 Subdivision Controls 10 SEPP Exempt & Complying Codes 12 Analysis of the controls 15 Understanding Slope 17 Slope Typologies 19 Slope / Elevation Length / Cut 20 Structural Systems 21 Traditional and Current Practice 23 Sloping sites and vegetation 31 Can and should housing respond better to slope? 33 Designing to Sloping Sites 33 Cut and fill options 36 Summary 40 Sloping sites survey form 43 How can I have a say? 45 Want to know more? 45 This house responds to its up slope allotment condition by incorporating car parking space to the lower part of the site with living space above in an elevated position. The balcony provides a good address to the street. The post and beam construction and split level floorplate configuration allows the site level change to take place within the building design. The strong front yard landscaping also contributes to the streetscape appeal and softens the level changes. Review of DCP A1 Residential and Tourist Development Code Discussion Paper 2 Sloping Sites - Managing Cut and Fill 3

4 Introduction Tweed Shire Council s Planning Reforms Unit is currently undertaking a review of Tweed Development Control Plan (DCP) Section A1 Residential and Tourist Design Code: Part A Dwelling Houses. An industry and community breakfast forum was held in September An issues paper was distributed at the forum highlighting some of the emerging issues and seeking both industry and community feedback on the current single dwelling controls and more importantly on what is working and what is not for the construction of houses and how new dwellings present in the streetscape. A range of issues have been identified. Each issue will be the subject of a discussion paper that will provide a summary of: the objectives and controls; what they seek to achieve; how is the housing market meeting or responding to these objectives and controls; is the finished housing outcome meeting the objectives; is the finished housing outcome meeting the owner s and neighbour s expectations; is the finished housing outcome integrating with the site and the neighbourhood; a range of options for amendment No amendments to the DCP have been made to date, the purpose of this discussion paper is to seek early input from the community and the development industry to identify what issues are important, what elements of housing are problematic or desirable. Council supports community engagement and best practice in the preparation of important strategic policy. Broad Actions Initial breakfast meeting Assessment of issues, drafting of discussion papers Consultation / feedback on discussion papers Drafting of DCP A1 amendments Public exhibition DCP A1 amendments Review submissions / final editing Report DCP A1 amendments to Council 4th qtr st qtr nd qtr rd qtr th qtr st qtr nd qtr rd qtr th qtr 2012 Indicative timeframe for the DCP A1 review 4

5 What issues will the review address? Based on internal reviews and both industry and community feedback to date, a range of issues will be consulted on through the following discussion papers: 1. Designing in context 2. Cut and Fill provisions and sloping sites 3. Landscaping and deep soil zones 4. Building envelopes - setback and height; floor space ratio and site coverage 5. Small lot design 6. Ancillary structures 7. DCP structure What about the other parts of the plan? In the first instance, the review concentrates on Part A, the controls that relate to dwelling houses, alterations and additions and ancillary development. Part B relates to dual occupancy housing, granny flats, town houses and row houses and Part C relates to residential flat buildings and shoptop housing. Whilst it is understood there is an overlap in content, Parts B and C will be reviewed in subsequent stages. What about major subdivision of land? It is acknowledged there is significant relationship between the subdivision of land (major subdivision) and the development of dwelling houses. The review of Part A, whilst a separate process, will be considered in the context of the subdivision codes and assessment practices, ascertaining any gaps and problems which flow on to housing development. The subdivision code (Part A5) will be the subject of a separate review. What will happen next? The issues will be the subject of a suite of discussion papers to be released for consultation over the coming months, and will be seeking both industry and community feedback on the issues and the options presented. Together the discussion papers and the feedback received will inform the review of DCP A1 Part A. Where required, draft amendments to the DCP will be prepared and reported to Council, which with Council s approval, will be publicly exhibited for comments. How long is this review likely to take? The first stage of the review commenced at the stakeholder breakfast in September This is now being followed by the staged release of the discussion papers, anticipated to be released for comment over the second half of The table on the facing page outlines the next steps and estimated timeframe. Review of DCP A1 Residential and Tourist Development Code Discussion Paper 2 Sloping Sites - Managing Cut and Fill 5

6 The Issues In the Tweed, like many other locations on the North Coast and South East Queensland there is a limited supply of available, flat, flood free land. Our investigation shows that of land (yet to be zoned) that may accommodate major greenfield development over the next 5-30 years, the mean slope is 9.8 degrees (approximately 18%), with large portions of these lands having a slope greater than 14 degrees (approximately 25%). The topography and vegetation in Tweed s urban and greenfield development areas is an important part of Tweed s landscape and visual character. This visual character is highly valued, as demonstrated through submissions to the Tweed Community Strategic Plan. Maintaining the integrity of the scenic background, natural topography, ridge lines, and treed landscape features is an important objective of the DCP, and is to be encouraged. As the supply of relatively level land diminishes, many new residential release areas turn to bulk land forming (see large batters above) at the subdivision stage to achieve less steep building sites. This bulk land forming may, under DCP Part A5 for residential subdivisions, permit finished surface levels that depart from natural surface levels by up to 5.0m and greater than 5.0m for no more than 10% of the site. Variations up to 15% may be considered where demonstrated environmental benefit. Sloping sites present a number of design challenges and generally require greater design input than flat sites. Sloping sites offer unique amenity opportunities that benefit from elevated positions including views and outlook, access to cooling breezes. Buildings that are designed to suit a sloping site often result in more interesting building forms which, when well designed, integrate within the landscape. Current building practice favours creating a level building site (benching) on which a single concrete slab on ground house can be easily constructed. In order to create a level building site on sloping land, extensive cutting and filling occurs and the construction of retaining walls, most often on property boundaries, is required. The perception is that this is easier and cheaper than designing to suit the slope, and frequently this is the only option considered. Many of the residential release areas have already been subject to substantial bulk earth works for subdivision, with residential subdivision controls allowing finished surface levels to depart from natural surface levels by up to 5m and greater than 5.0m to no more than 10% of the site. Any subsequent earthworks post subdivision represent a further recontouring of the natural topography and further compromises the landscape integrity of undulating residential land and the scenic background to the locality. Extensive site earthworks above have resulted in a large double tiered rock retaining wall running the full width of the block. This leads to awkward interface issues with the adjoining property and will require a fence on top to comply with the BCA. Many landowners, builders and designers are seeking to place single level, generic house designs onto land parcels that cannot easily be accommodated on the sloping sites without extensive cutting and filling. In effect, the emerging practice is for the site to be modified to fit the house, where traditionally the house was designed to fit the site. 6

7 Modifying the site to fit the house impacts on the visual presentation of the locality. The built form and streetscape tends to take on a stepped appearance, losing the natural rhythm of the topography and appearing disjointed. We would like to know how the community perceives this approach to construction. In addition to the wider visual appearance of the streetscape, this form of construction also impacts on the residents of the site and adjoining sites. Some of the impacts of full width site benching include: Both photos show how site benching has resulted in significant side retaining walls with its overall height amplified by the dividing fence on top of the wall. This results in an overlooked and significantly overshadowed backyard. The use of a timber retaining wall could result in its structural integrity being undermined in the future which could lead to drainage issues and landslip. Creation of awkward boundary interfaces, often resulting in large costly retaining walls. The construction of large retaining walls, which have the potential to detrimentally impact on the amenity of an area and add considerably to the cost of the land and/or the proposed development for the end customer. Building large retaining walls on the boundaries of an individual lot may give rise to drainage and subsidence issues if construction is not structurally appropriate. Erection of a dividing fence on top of the extensive retaining wall to maintain privacy and safety, which in effect significantly increases the overall height at the boundary (often over 3.0m) resulting in unsightly walls, in a range of various materials, overshadowing and overlooking issues. Deep excavation cuts disturbing the pattern of subsoil water flow and soil stability which may adversely affect neighbouring properties and the natural environment. The filling of front yards on up slope blocks to achieve a level area impacts the visual quality and streetscape character by creating a wall or large earthen berm to the street edge. excessively steep driveways. The issue of cut and fill is the single most challenged control in the Tweed DCP A1. There is currently a lack of understanding of designing to slope, of slope appropriate housing being offered by the volume housing builders and a lack of development control guidelines to achieve appropriately structured housing on slopes greater than 10 degrees (approximately 18%). In the photo above the side fencing steps at 5 different levels within the side boundary of the two dwellings. Review of DCP A1 Residential and Tourist Development Code Discussion Paper 2 Sloping Sites - Managing Cut and Fill 7

8 Current Statutory Requirements DCP A1 Residential & Tourist Development Code The current objectives for topography, cut and fill in relation to dwelling houses are: to retain the existing landform to limit the extent of excavation to moderate the effects of building height and bulk on sloping land to minimise the extent of earth works on residential land and earthworks associated with residential development to ensure that the building design is appropriate for site s topographical conditions to ensure development is sympathetic with the existing topography and water cycle of the site The current controls for topography, cut and fill in relation to dwelling houses are: Building siting is to relate to the original form of the land. Alternatives to slab on ground construction are to be encouraged where it is obvious that due to the gradient and characteristics of the site, major excavation or filling as a result of raft slab construction would be inappropriate. Examples of alternative construction includes: Bearer and joist construction; Deepened edge beam; Split level design; Suspended slab design. On sloping sites step buildings or utilise site excavation and suspended floors to accommodate changes in level rather than levelling the site via cut and fill. Dwellings must not be designed to be on a contiguous slab on ground type if the building site has a slope of greater than 10%. Development on such land is to be of pole or pier construction or multiple slabs or the like that minimise the extent of cut and fill. Site excavation / land reforming is to be kept to a minimum required for an appropriately designed site responsive development. The maximum level of cut is 1m and fill is 1m. Retaining walls maximum 1.2m. Cut areas are to be set back from the boundaries at least 900mm; fill areas are to be setback from the boundary a minimum of 1.5m. Cut and fill batters shall not exceed a slope of 1:2 (v:h) unless geotechnical reports result in Council being satisfied with the site stability. All batters are to be provided with both short term and long term stabilisation to prevent soil erosion. Excavations in excess of one metre within the confines of the building and on driveways may be permitted, to allow for basement garages providing the excavations are adequately retained and drained, in accordance with engineering details. Filled areas are to be located where they will not impact on the privacy of neighbours. Stormwater or surface water runoff shall not be redirected or concentrated onto adjoining properties so as to cause a nuisance and adequate drainage is to be provided to divert water away from batters. The top of any battered cut (or retaining wall) and the toe of any battered fill (or retaining wall) is not to be closer than 900mm for cut and 1.5m for fill to any property boundary, where the overall height at any point exceeds 500mm. The current variations provisions to Cut and Fill Design Variations to the requirements above will be permitted to create a flat yard space not exceeding 15% of the area of the lot for the purposes of outdoor living, recreation, clothes drying, swimming pool and the like. Proposed variations to the controls must demonstrate that the excavation or filling of the site is in harmony with the natural landform/environment and will not adversely affect the adjoining properties. Where a property is burdened by stormwater or water and sewerage mains then Council will generally preclude any excavation or filling within that easement. 8

9 What is the purpose of cut and fill development controls? The inclusion in the DCP of objectives and controls for cut and fill is to manage the impact on the natural environment including drainage, soils stability, structural integrity, privacy of adjoining neighbours, and the visual impact on the streetscape of substantially changing landforms. GPA Architects This house responds to its up slope by having its garage recessed under a projecting upper level balcony. Part of the upper level is suspended reducing the need for full site width cut and fill. The nominal setbacks to buildings and the on site drainage requirements are generally easily managed on relatively flat sites, without undue impact to the adjoining properties or significant visual impact on the streetscape. However, as the slope of land increases, there is the potential for greater impacts and the need for greater design detail to manage those impacts. What is desirable? The DCP cut and fill provisions seek to find a balance that: This house responds to its side slope by having its garage on the lower level with living space above. The visual impact of the double garage is reduced by projecting balconies which provide the occupants with good outdoor living space, and access to views, breezes and light. ensures housing selection and design understands and responds to the topography of the area; discourages recontouring of land post subdivision as being the preferred method of construction; promotes the retention of the existing topography resulting in the houses retaining a consistent relationship with the natural topography; creates greater flexibility to ensure design responds to slope appropriately, encourages a more holistic approach to site planning and provides for appropriate cut and fill over slope categories to allow a range of housing choice; moderates the effects of building height, bulk and mass on sloping land; reduces the instance of drainage problems and retaining wall subsidence; provides guidances for sites that may have a slope greater than 10 degrees (approximately 18 %); considers the wider community impacts such as streetscape, privacy, overshadowing, access to breezes; facilitates home owner requirements, such as good housing design, usable outdoor spaces; and does not unduly impact on housing affordability. This house responds to its down slope by suspending part of the upper floor, and having half a level down slope reducing the amount of cut and fill required. Review of DCP A1 Residential and Tourist Development Code Discussion Paper 2 Sloping Sites - Managing Cut and Fill 9

10 DCP A5 Subdivision Controls What is the relationship of the cut and fill provisions with the subdivision requirements? Part A5 of the DCP contains the controls in relation to subdivision. This part of the DCP clearly articulates the need for undertaking a site analysis to ensure that the context of the location and the opportunities and the constraints of a residential release site are considered in the evolving design iterations. This section of the DCP requires, in summary, in relation to land forming that: Land forming should be kept to a minimum; Subdivision should be designed to fit the topography rather than altering the topography to fit the subdivision; Land forming should preserve levels at site boundaries and retaining walls to, or within 3m, of the boundaries should not exceed 1.2m; For residential land uses, the proportion of a site that contains cut and fill areas with finished surface levels that depart from natural surface levels by more than 5m shall not exceed 10%. Variations up to 15% of the site area may be considered if such variations have a demonstrated environmental benefit; Batters and retaining walls are not permitted for the purpose of creating terraced lots; The finished landform should mimic existing and local surrounding natural topography; For residential subdivisions, the combined height of retaining walls or cut and fill batters on an allotment boundary shall not exceed 1.2m at boundary, 1.8m above street level and 2.4m below street level; Scenic Impact Assessment is required for subdivisions of more than 50 lots or 15,000m2 of earthworks. From the above it can be seen that the residential subdivision requirements maintain similar objectives with regard to undertaking rigorous site analysis and seek similar management of sloping sites, essentially that subdivision should be designed to fit the topography rather than altering the topography to fit the subdivision. Notwithstanding, the subdivision controls allow land forming whereby the finished ground surface levels may depart from natural surface levels by up to more than 5m and not exceeding 10% of the site. For large residential release areas this has a significant impact on the natural landform, topography and visual appearance. It is a common practice within new land release areas to include retaining walls to terrace land to enable flatter building sites. 10

11 These terrace sites are then further modified with additional cut and fill to enable a slab on ground dwelling to be constructed. In general, individual site cut and fill requirements have been kept to a minimum as significant land forming is frequently already undertaken at the subdivision stage. The perception is that the market is demanding single level slab on ground dwellings. However, as part of this process we are also interested in finding out if the people choosing new housing: understand the process of site analysis and responsive design; are aware of other construction options and/or their costs; or are offered other choices by housing providers. Your feedback is sought In your opinion is land forming at the subdivision stage acceptable? Do you think that more cut and fill to a site, which has already been altered is acceptable? Significant land forming has been carried out to create these subdivisions resulting in recontouring of the topography to remove many hills and create flatter building sites. This results in many substantial sections of retaining walls and large areas of earth batters. Review of DCP A1 Residential and Tourist Development Code Discussion Paper 2 Sloping Sites - Managing Cut and Fill 11

12 SEPP Exempt & Complying Codes Relationship with the State Environmental Planning Policy (Exempt and Complying Development Codes) 2008 The Code SEPP is a State Government policy which allows for single dwellings and alterations and additions to single dwellings (and other specified development), which meet a standardised range of development standards, to be lodged and processed in an expedited manner, i.e. within 10 days. The Code SEPP is a state wide and generic suite of controls aimed at stimulating housing construction and speeding up the assessment time for development which the State percieves to be low impact. The Codes SEPP for complying development requires, with regard to earthworks and drainage, specifically cut and fill, works must be consistent with the following: 3.29 Excavation of sloping sites 1. Excavation associated with the erection of, or alterations or additions to, a dwelling house or ancillary development (other than a swimming pool) must: a. be not more than 1m below ground level (existing), and b. be constructed using a retaining wall or unprotected embankment that meets the standards of sub-clause (2) or (3), respectively. 2. A retaining wall: a. must not redirect the flow of surface water onto adjoining property, and b. must not extend more than 2m horizontally from any external wall of the dwelling house or ancillary development. 3. An unprotected embankment must not extend more than 2m horizontally beyond the external wall of the dwelling house or ancillary development. 4. Excavation associated with the erection of, or alterations or additions to, a swimming pool must be not more than the depth required for the pool structure. 12

13 3.30 Fill of sloping sites 1. Fill associated with the erection of, or an alteration or addition to, a dwelling house or ancillary development must: a. be contained wholly within the footprint of the dwelling house or ancillary development, or b. be adequately contained by a retaining wall that: (i) is not higher than 600mm (including the height of any batters) above ground level (existing), and (ii) does not redirect the flow of surface water onto adjoining property. 2. Despite sub-clause (1), exposed fill may be constructed using an unprotected embankment if the dwelling house or ancillary development has a setback of more than 2m from a side or rear boundary, if: a. the fill is not more than 600mm above ground level (existing), and b. the fill (but not the embankment) does not extend more than 1m beyond an external wall of the dwelling house or ancillary development, and c. the toe of the unprotected embankment has a setback of at least 400mm from a side or rear boundary. Analysis Complying development applications must meet these standards (and a range of other development standards), otherwise the application is lodged as a standard development application and the development standards of the local Council DCP apply. The Tweed DCP is a suite of controls developed to meet a wide range of situations and development types. The differing objectives of this plan to the Code SEPP means there will be some minor variations within the controls. In regard to cut and fill both the Code SEPP and the Tweed DCP A1 provisions have a consistent intent. The DCP A1 requirements for cut and fill are currently more generous than the SEPP Code requirements, as a DA and greater assessment is required. Council s DCP A1 currently allows +/-1.0m cut and fill across a site where as the SEPP Code only allows 1.0m cut and 600mm fill within the confines of the building envelope. Additionally, retaining walls are not required to be limited to within 2m of the wall of a dwelling house in the current DCP A1 controls. Both DCP A1 and the Code SEPP require that drainage is to be managed on site and water is not to flow onto adjoining properties. Review of DCP A1 Residential and Tourist Development Code Discussion Paper 2 Sloping Sites - Managing Cut and Fill 13

14 15.0m HOW MUCH CUT AND FILL IS ACCEPTABLE ON A TYPICAL RESIDENTIAL LOT? The diagram above illustrates the relationship between site benching, slope and retaining wall height, based on standard volume housing dimensions and setbacks. Current controls limit cut and fill to 1.0m across typical residential allotments and limit continuous slabs to slopes of 10 degrees (approximately 18%) and less. 14

15 Analysis of the Controls Your feedback is sought In your opinion do houses with high retaining walls have a negative impact on the streetscape? In your opinion do large changes in levels between houses affect privacy or access to sunlight? Analysis of the effectiveness of the controls Whilst cut and fill controls apply to all sites and housing development applications, they are generally the most relevant to construction of a single level contiguous slab. As the current maximum cut & fill level is +/- 1 metre, over an averaged sized project home elevation length a continuous slab construction can only be accommodated on slopes up to 4 degrees, or 7%, as shown in the Diagram opposite. This would still result in a rear retaining wall approximately 1153mm high. The current provisions do not suitably provide guidance or qualitative objectives for greater slope situations. Thus, there is increasing pressure to solve the issue by increasing the permissible cut and fill and resultant retain walls. A common situation, particularly on down slope lots, is that in addition to a 1500mm high retaining wall, most sites then include an 1800mm fence above effectively increasing the walled effect to around 2.3m at the rear boundary interface. These sites generally also include a significant earth berm or retaining wall to the street elevation. Current practice of site benching houses on slopes up to 10% (approximately 18%), increases the rear boundary interface to approximately 4.7m and the side boundary interface to approximately 3.5m to accommodate a typical continuous slab on ground home creating a enclosing wall effect to many rear yards. Thus the current topography, cut and fill controls (d), (f) and (g) do not relate as well as they should and on many sites cannot be achieved. Depending on the design of neighbouring houses, such as balconies or verandahs on the up slope house, and how close the house is built to the boundary, this greatly increases privacy impacts and overlooking into neighbouring houses and yards. This form of siting of houses greatly alters the streetscape creating a stepped appearance and greater housing bulk and visual impact than siting that follows the contours of the site. An issue of streetscape and designing an appropriate street address also arises where a large retaining wall or batter is located in the front setback, or on the property s front boundary. This results in very steep driveway access, exacerbates drainage requirements and depending on orientation may reduce access to sunshine, shade or cooling breezes. Review of DCP A1 Residential and Tourist Development Code Discussion Paper 2 Sloping Sites - Managing Cut and Fill 15

16 Flat Site (0-10%) Moderate Slope (10-21%) Steep Slope over (21-32%) Extreme Slope over 20 0 (over 32%) 16

17 Understanding Slope Calculating Slope Convert Degree to Percent RISE TAN RISE RUN TAN % RISE (ANGLE) DEGREES PERCENT RUN RUN SLOPE ANGLE (DEGREES) SLOPE PERCENT % % % % % % % % % % % % % % % % % % % % To understand the cut and fill provisions, it is first crucial to understand slope. One of the characteristics of a quality and livable house is that it is designed to suit the specific site conditions rather than trying to significantly alter the site through earthworks to enable a pre-determined building and structural system. Recognising the type of slope you are designing for and understanding what might be an appropriate structural system to employ for a particular site is imperative to good design. Slope can be divided into four broad typologies, each which require different design considerations: Up slope Down slope Side Slope Rolling Slope (two or more slopes) For the purpose of this discussion paper, degree of slope has been divided into four broad categories: Flat 0-6 degrees - approximately 10% Moderate 6-12 degrees - approximately 21% Steep degrees - approximately 32% Extreme 20 degrees and over - > approx 32% Why planning for site and slope is important A site and slope responsive design minimises cut and fill, and maintains the integrity of the natural landscape and character of a locality while significantly improving streetscape appearance. The maintenance of the natural topography is a key objective in terms of preserving the Tweed s landscape and visual character. Conversely, the cumulative visual impact of subdivision wide site benching and construction of large retaining walls impacts streetscape character, which in turn impacts on locality and shire wide character. The levelling or benching of sloping blocks also then limits the built form variety which can be constructed across the site. It is, however, understood that an element of flat land is important on sloping blocks for a car space, clothes line, outdoor entertaining area and place for kids to play. It is therefore important to understand what is an appropriate balance of cut and fill to both meet individual lifestyle requirements and maintain the visual and landscape character of the Tweed. Review of DCP A1 Residential and Tourist Development Code Discussion Paper 2 Sloping Sites - Managing Cut and Fill 17

18 On downsloping blocks going up a storey to the rear significantly increases the overall building height and mass to the rear elevation DOWNSLOPE Characteristics Site falls away on the low side of the road. Garage doors and driveways are generally positioned closer to road edge to avoid steeply sloping driveways often making it difficult to comply with the 1.0m setback to the front door. More likely to have a rear deck taking advantage of elevation, natural light access, breeze and view in split level or two storey design. More likely to require excavation to accommodate a lower (half) level which often exceeds 1.0m but is concealed from view from the road. Living spaces often disconnected from backyard due to preference for living space to be elevated taking advantage of elevation, natural light access, breezes and views. More likely to appear bulky and visually prominent from down slope elevation if not integrated with the slope. Potential for privacy and overlooking issues for adjoining neighbours to rear backyards. On up sloping blocks care needs to be taken with treatment of earthen berms or retaining walls to the front facade. In very steep locations, the visual intrusion of retaining walls becomes significant and dwellings may sit on the modified topography rather than integrating with the topography. 18 UPSLOPE Characteristics Site rises up from the street. Generally requires more cut to allow lower / level / garage for two-storey or cut and fill to create a level platform for construction. Garage doors and driveways are generally more visually dominant from the street. More likely to have a front deck over looking the street in two storey design. Living spaces often well connected to backyard with level transition from living space to rear yard. Often results in excavation and need for retaining walls to rear yard to create a flat backyard area. More likely to require excavation, which often exceeds 1.0m, to accommodate a part lower level. More likely to appear bulky and visually prominent from the street.

19 Slope Typologies Full width site benching has resulted in significant retaining wall elements to the side boundary. Once the boundary fence is added the effective neighbouring building height is over 3 stories. In addition to privacy and overlooking concerns, if this occurs on the northern boundary the lower house is substantially overshadowed. SIDESLOPE Characteristics Site falls across the site from side boundary to side boundary. Traditionally, garage doors and driveways positioned on the lower side of the block, however, recent practice tends to position on the high side to achieve level transition between street, living space and backyard. Opportunity for elevated deck to take advantage of the elevation, natural light access, breezes and views. More likely to require excavation to accommodate a part lower level (garage) which often exceeds 1.0m within the building envelope and is often a full level (2.9m). Can achieve good relationship and level transition from living space into the backyard. More likely to require creating a wall or earthen berm to side boundary. More likely to create a stepped streetscape appearance. Potential for privacy and overlooking issues for adjoining neighbours to the lower side. ROLLING SLOPE Characteristics Site slopes in two or more directions. Most sloping sites also have an element of cross fall combined with an up or down slope depending on the site s relationship with road access. Rolling slope lots provide the opportunity to explore house design with split levels to step with the slope of the site or take up the level change within the building. The house above uses the undercroft of the deck as a car space and integrates well with the landscaped garden. Garage doors and driveways are generally positioned on the lower side of the block to reduce the amount of cut and fill. More likely to have a deck over the garage taking advantage of the elevation, breezes and views. More likely to require excavation to accommodate a part lower level (garage) which often exceeds 1.0m within the building envelope and is often a full level (2.9m). Depending on up or down slope relationship, living spaces can often be disconnected from backyard due to the elevated living space away from the street interface. Review of DCP A1 Residential and Tourist Development Code Discussion Paper 2 Sloping Sites - Managing Cut and Fill 19

20 Slope / Elevation Length / Cut Elevation Length Cut / Fill Required Slope 2 o Slope 4 o Slope 6 o 8m +/- 0.28m +/- 0.55m +/- 0.84m 10m +/- 0.35m +/- 0.69m +/- 1.05m 12m +/- 0.42m +/- 0.84m +/- 1.26m 14m +/- 0.48m +/- 0.98m +/- 1.47m 16m +/- 0.56m +/- 1.11m +/- 1.68m 18m +/- 0.63m +/- 1.26m +/- 1.89m 20m +/- 0.70m +/- 1.40m +/- 2.10m or 0-10% Denotes compliance with current cut and fill provisions of +/-1.0m or 14-20% Elevation Length Cut / Fill Required Slope 8 o Slope 10 o Slope 12 o 8m +/- 1.12m +/- 1.41m +/- 1.70m 10m +/- 1.40m +/- 1.76m +/- 2.12m 12m +/- 1.69m +/- 2.16m +/- 2.55m 14m +/- 1.97m +/- 2.47m +/- 2.97m 16m +/- 2.25m +/- 2.82m +/- 3.40m 18m +/- 2.53m +/- 3.17m +/- 3.80m 20m +/- 2.81m +/- 3.53m +/- 4.25m Elevation Length Cut / Fill Required or 25-30% Slope 14 o Slope 16 o Slope 18 o 8m +/- 1.99m +/- 2.29m +/- 2.60m 10m +/- 2.49m +/- 2.86m +/- 3.25m 12m +/- 2.99m +/- 3.44m +/- 3.90m 14m +/- 3.49m +/- 4.00m +/- 4.55m 16m +/- 3.98m +/- 4.58m +/- 5.20m 18m +/- 4.48m +/- 5.16m +/- 5.84m 20m +/- 4.98m +/- 5.73m +/- 6.50m The above sliding scales illustrates the limited ability of a single slab on ground construction to comply with the +/- 1.0m cut and fill requirement including site slopes of 2 0, 4 0, and 6 0 (only where the elevation length is less than 8.0m). The sliding scales demonstrate that even if the amount of cut and fill was increased to 1.5m, the continuous slab would only comply in a limited capacity. This reinforces the need for houses on sloping blocks to take up level change within the building which will reduce the need for large retaining walls at site boundaries. 20

21 Structural Systems Single Slab on Ground (Controlled to 6 degrees only) Single reinforced concrete slab; Appropriate on sites up to 6 degrees, over 6 degrees typically requires significant cut and fill and retaining walls; Require minimal site preparation on flat sites; Require drainage at base of concrete slab; Conducive to project home design. ArcoEco Architects Split or Raft Slabs (Typically degrees) Two or more reinforced concrete slabs at different levels; Allows building design to follow the slope of the site; Can easily take up level change (up to 2.7m) within building design; Good for side sloping blocks; Drop edge beam becomes a waterproofed retaining element. Good for taking up level change within building; Results in more interesting internal arrangement and varying ceiling heights including higher volumes over living, dining and kitchen areas. Part slab / Part Suspended (Typically 6-18 degrees) Structure often results in a half lower floor (on slab) with upper level being part suspended / post and beam Allows good internal transition to backyards / street; Good for taking up level change within building. Good for moderately sloping sites; Reduced downstairs area minimises the amount of site cut and fill. Suspended or Platform (Typically degrees) Typically preferred structural approach on steeply sloping lots; Timber or steel post and beam construction; Minimal site cut and fill significantly reduces site preparation works; Conducive to light weight materials and split level designs; Opportunity to infill lower portion as an extension; Less likely to have drainage issues with surface water able to flow across site. Review of DCP A1 Residential and Tourist Development Code Discussion Paper 2 Sloping Sites - Managing Cut and Fill 21

22 Traditional responses to slope Current responses to slope In many traditional established areas the natural topography has largely been retained. Roads and allotments have been planned to follow the slope and the areas exhibit a diversity of dwellings and landscape elements. In newly established areas, the natural topography has predominantly been altered through significant land forming to remove the slopes and create flatter building areas. Methods of managing slope in traditional established areas are frequently built into the public areas and form part of the consistency and character of the locality. Methods of managing the slope in newly established areas are predominantly confined to the individual properties and exhibits a wide range of treatments and materials. 22 Most traditional areas display visually discrete or period style fencing. In may locations there is an absence of fencing, instead relying on a landscaped corridor. Newly established areas tend to rely heavily on visually prominent colourbond fencing.

23 Traditional and Current Practice Many established areas of the Tweed enjoy elevated, sloping aspects that take advantage of the scenic views, elevated positions and cooling breezes. Traditionally, the sloping sites were not subject to significant bulk earthworks, instead the subdivisions are characterised by roads that both follow and cross contours, providing visual interest and enabling a variety of housing forms and allotment sizes. This results in a more diverse character and more diverse housing forms. Where retaining walls are used, the materials are generally more natural, such as dry stone walls and rock walls. In established areas the retaining walls form part of the public landscape of the area, highlighting changes in public or private spaces, delineating walkways and incorporating landscaping elements. Newly established areas predominantly use retaining walls within the private zones as a means of achieving a flat yard area, often with little integration to the interface with the public spaces. Characteristic of the traditional areas is the extensive mature vegetation. Trees soften the harsher elements of the landscape and have a healing effect on the scaring of altering the landfrom. Clearly newly established areas require time for the mature vegetation to establish and soften the landscape appearance, however, the emerging character of the newly established areas is one of low scale shrub landscaping and a noticeable absence of larger tree species. This leaves the land forming and resulting retaining walls and fencing as an obvious visual element. The traditional established areas generally contain visually discrete fencing, predominantly timber paling, which blends with the natural elements of the landscape. In many areas there is no fencing, instead privacy to individual properties is achieved through landscaped corridors along the boundaries. The predominant character of the newly established areas is the use of colourbond fencing and in the absence of significant landscaping, this has a tendency to become a predominant feature of the streetscape, exacerbated when on top of retaining walls. Each of these landscape characteristics creates the character of the street or locality, whereby, generally, housing in traditional areas integrates within the landscape and offers a unique and diverse character. The emerging character of newly established areas is of housing that sits on top of the landscape and offers less diversity in form and character and negates the benefits of elevated view and cooling breeze. Review of DCP A1 Residential and Tourist Development Code Discussion Paper 2 Sloping Sites - Managing Cut and Fill 23

24 Traditional responses to side slope Current responses to side slope Traditionally the dwellings are constructed in a split level form following the contours of the land. This results in a streetscape that flows with, and replicates the natural topography. More recently dwellings are being constructed as a single level slab on ground. This results in significant full site width cut and fill and the characteristic stepped streetscape, where dwellings sit on the altered topography. Traditionally there is no side boundary retaining wall as the house follows the natural topography. More recent construction seeks to maintain a single level dwelling and relies heavily on full width site cut and fill which results in significant level changes between the side boundaries, the need for retaining walls and a mosaic of fencing treatments and heights. Traditionally dwellings were constructed as a split level form, generally with the garage below the dwelling on the low side of the slope. This enables the dwelling to integrate with the natural topography. More recent construction favours a single level dwelling which requires the site to be levelled to accommodate the dwelling and results in significant land reshaping. 24

25 Side slopes Your feedback is sought Do you have an opinion on the way housing looks when the site is subject to extensive site benching to level the site? Do you think that this creates privacy or overshadowing impacts? Are these issues of importance to you? Do you think that the construction method of cut and fill is OK for sloping sites? Would you prefer to see housing that integrates with the natural topography? 8.5m Traditionally the dwellings on side slopes have been generally constructed in a split level form, with the garage occupying the lower level. The split in levels is accommodated within the building footprint, generally resulting in different levels between the front door and the garage entry. Accommodating the level change within the dwelling removes the need to create level changes across the width of the site. In examples reviewed, the change in level within the building footprint can be up to a full storey ( m). However, this results in very little retaining wall construction required between houses as the change in level is accommodated within the building footprint and dwelling, rather than across the site. With this form of development the dwelling integrates with the slope and the built form of the streetscape flows with and replicates the natural topography. The more recent trends are for single level housing on a concrete slab. The housing market appears to prefer this form as it is perceived to be more cost efficient, maintains all living on a single level and enables the creation of flat yard spaces. However, this form of housing frequently results in overshadowing and overlooking issues, steeper driveway access and extensive and costly earth retaining measures. It also significantly impacts on regional views and streetscape appearance with large, often unlandscaped, retaining walls at boundaries. As the houses do not respond to slope, the resultant building form is also of less architectural or visual interest. As part of this consultation, Council is seeking feedback from the industry and the community on their perceptions of the built form outcomes of houses on slopes. ELEVATED POSITION PROVIDES MORE ACCESS TO PREVAILING BREEZES SIDE BALCONY PROVIDES VIEW & EXTERNAL LIVING AREA GARAGE AT LOWER LEVEL & CARPORT UNDER DECK 9m SIDE BUILDING STEPS WITH SLOPE CREATING DIFFERENT INTERNAL VOLUMES WINTER SUN 33 o EASY TRANSITION BETWEEN LIVING SPACE AND REAR / SIDE YARD SIDE SIDE BOUNDARY Side Slope Design Principles LEVEL CHANGE TAKEN UP WITHIN BUILDING DESIGN RATHER THAN SIDE BOUNDARIES Review of DCP A1 Residential and Tourist Development Code Discussion Paper 2 Sloping Sites - Managing Cut and Fill 25

26 Traditional responses to down slope Current responses to down slope Traditionally down slope dwellings are constructed in a split level form following the contours of the land. This results in a streetscape that flows with, and replicates the natural topography. More recent construction seeks to maintain a single level transition from the street and double garage to living spaces, reducing the need for steps between. In attempt to maintain the 6.0m setback this house is forced down the hill creating an sunken street interface. Traditionally narrower building footprints running across the site reduced the amount of cut and fill required. This split level house utilises the flatter front yard as outdoor living space. More recently, down slope dwellings are constructed as a single level slab on ground to the street with 2 or sometimes 3 storeys to the rear of the allotment. This results in significant building height and bulk to the rear elevation, leading to overshadowing and overlooking issues. Traditionally dwellings on down slopes have a less front setback and a more generous front deck which addresses the street, with two storeys to the rear (undercroft often for storage). Garages are either located to the rear of the site, or as lightweight carports to the side enabling access directly off the street. New dwellings are required to comply with a 6.0m front setback irrespective of an up slope, down slope or side slope configuration. On down slope lots, garages are more difficult to integrate with dwelling design, often resulting in a significant amount of hardstand driveway and manoeuvring space. 26

27 Down slopes The lots in down slope areas are commonly smaller. Traditionally dwellings in down slope areas respond to the topography by entering at, or lower than, street level, with single storey to the street and two storeys or a split level to the rear. Where appropriate rear balconies are often included. Depending on the subdivision character, garages are typically located either down slope to the rear of the property or suspended at street level to the front of the property. Dwelling are frequently set closer to the front boundary, with the property hugging into the slope. Many traditionally sloping areas incorporate rear lane ways for garaging, thus also providing vehicular access at a different level to the front door access. This again accommodates the level changes within the building footprint. In more contemporary down slope examples, dwellings often present as a single storey to the street with two and sometimes three storeys to the 9m rear. Whilst from the street the building appears of an appropriate scale, the side and rear elevations are longer, higher and bulkier than traditional counterparts accommodating increased floorspace requirements. This can lead to overlooking and overshadowing issues and a series of balconies which rarely get used. On down slope allotments the garage or carport is more visible from the street, and arguably more difficult to integrate into the design of the house. In newer development this is made more difficult by the 6.0m front setback and requirement that the garages should be 1.0m behind the buildings front elevation. This increases the amount of hardstand area and can create a level disconnect between the garage and house on down slope allotments. These requirements to a large extent shape the front elevation of newer developments as designs seek to meet the minimum requirements, in effect creating a more homogenous streetscape, rather than encouraging a built form which responds to the slope. 9m 9m ELEVATED POSITION PROVIDES MORE ACCESS TO PREVAILING BREEZES BUILDING STEPS WITH SLOPE CREATING DIFFERENT INTERNAL VOLUMES EASY TRANSITION BETWEEN STREET AND LIGHTWEIGHT CAR PORT / GARAGE GARAGE DESIGN TO INTEGRATE WITH HOUSE DESIGN STREET REAR BALCONY PROVIDES VIEW EXTERNAL LIVING AREA TRANSITION BETWEEN LOWER FLOOR AND REAR YARD REAR 9m Down Slope Design Principles LEVEL CHANGE TAKEN UP WITHIN BUILDING DESIGN Review of DCP A1 Residential and Tourist Development Code Discussion Paper 2 Sloping Sites - Managing Cut and Fill 27

28 Traditional responses to up slope Current responses to up slope Traditionally up slope dwellings have deeper front yards to take advantage of elevated views and access to cooling breezes. This often results in garages or carports being detached located at a lower level on the site. In more recent up slope designs, dwellings are often only set back the requisite 6.0m from the front building line to maximise the development footprint over the site. In terms of floorplan configuration, many new dwellings fail to integrate internal living spaces with rear yards. Deeper front yards provide more opportunity for significant landscaping. This above detached garage has been used as an elevated outdoor terrace. Large elevated balconies taking advantage of view and breezes feature prominently on the buildings front elevation. More recent construction seeks to maintain a single level building platform in order to build a continuous slab on ground dwelling. In the above example this has resulted in a significant retaining wall on the street edge dominating the streetscape exacerbated by the up slope. Traditionally dwellings on the upslope lots have a strong relationship with the street and a clearly identifiable pedestrian entrance, landscaped front yard and elevated front porch or balcony. The single car garage integrates with the overall building design. This house addresses the up sloping site with a small footprint excavation for the garage area and suspended post and beam structural system for the upper level allowing cooling air circulation around the house. The inclusion of a balcony onto the front elevation would have more successfully addressed the street. Landscaping rather than a large grassed area would also help to integrate the building with the slope. 28

29 Up slopes In older subdivision areas, lots on the up slope were frequently larger with the dwellings set back further from the street boundary to take advantage of views and cooling breezes. This also resulted in large landscaped front yards which now contribute strongly to streetscape character. 8.5m Depending on the severity of the slope and the character of the established areas, garages are sometimes located separately to the front boundary of the property, sometimes angled across the slope to a side entry, and at other times accessed through rear lane ways at a different level. This again accommodates the level changes within the building footprint, which is the prevailing characteristic of traditional responses to construction of dwellings on sloping sites. 9m In more recent up slope designs, dwellings are often only set back the requisite 6.0m from the front building line to maximise the development footprint over the site. This often leads to more of a built form weighting towards the street elevation, often two storeys and to within 900mm of the side boundaries. These larger floor plate dwellings leave little room for vegetation to grow up between up slope blocks, which would have otherwise softened or served to reduce the visual bulk of the dwelling. 9m There are also two broad construction types used on more recent up sloping blocks. The first is to cut and fill creating a flat platform to build a single or double storey house of a continuous slab and then retrofitting or shaping large retaining walls to the front and rear of the site to accommodate the level change. The second technique is to excavate a part lower floor for garage and guest room with a suspended upper level with bedrooms and living areas to the upper level. Despite this later structural type providing a desirable level transition from living space to the rear yard, many floor plan configurations fail to capitalise on this access, instead having services including laundries and bathrooms as interfaces with the rear yard. ELEVATED POSITION PROVIDES MORE ACCESS TO PREVAILING BREEZES BUILDING STEPS WITH SLOPE CREATING DIFFERENT INTERNAL VOLUMES WINTER SUN 33 o LEVEL TRANSITION BETWEEN LIVING SPACE AND REAR YARD SMALL REAR CUT CREATES FLAT AREA FOR EXTERNAL LIVING REAR FRONT BALCONY PROVIDES VIEW TO STREET AND BEYOND 9m STREET Up Slope Design Principles LEVEL CHANGE TAKEN UP WITHIN BUILDING DESIGN Review of DCP A1 Residential and Tourist Development Code Discussion Paper 2 Sloping Sites - Managing Cut and Fill 29

30 Traditional responses to landscape Current responses to landscape Extensive landscaping and greening of front and rear yards substantially improves streetscape character and the ability of a dwelling to nestle into the landscape. Landscaping can soften the scarring of excavation and conceal unsightly undercroft services. Whilst recent development has not had the benefit of time for substantial landscape to grow up, there is a growing trend to reduce the amount of landscape areas and especially planting of trees that will grow into more substantial species. This is replaced by small mulched garden beds with small shrubs and larger grassed areas. 30

31 Sloping sites and vegetation How does this improve the appearance of development on sloping sites? Your feedback is sought Do you think that planting softens the transition of changes in slope and levels? Why is there less vegetation, especially trees, being planted in newer developments? In this review and search for examples of how to construct dwellings on sloping sites, looking at what works and what doesn t, vegetation has stood out as a key consideration in designing for and constructing on sloping sites. A key characteristic of the established steep areas is that trees and substantial vegetation has either been retained following construction of a dwelling or has been substantially replanted with larger species, including trees. This has the effect of softening the scars of any cut and fill, hiding large undercrofts of dwellings and earth berms, integrating the dwelling more with the natural environment, and blending the built response to the slope with the natural topography. Newly established areas, generally are characterised by the absence of mature vegetation. Over time it would be expected that vegetation grows up and provides a similar type of screening as is typically found in the established areas. However, there is a noticeable lack of substantial vegetation, specifically trees, being planted. Instead vegetation is generally ornamental low growing shrubbery. The benefits of planting with appropriate trees, in appropriate locations are not just limited to visual appearance. Well located vegetation also assists with moderation of the micro climate around a dwelling, shading to exposed western aspects, privacy where topography results in overshadowing and greatly assists with integrating the outdoor spaces with the indoor spaces. As part of this review we are seeking comments on the possibility of linking vegetation requirements with cut and fill. Review of DCP A1 Residential and Tourist Development Code Discussion Paper 2 Sloping Sites - Managing Cut and Fill 31

32 NATURAL GROUND LEVEL LIMITED OPPORTUNITY FOR SIDE BOUNDARY LANDSCAPE OVERSHADOWING BY RETAINING WALLS AND FENCES HOUSE DESIGN FAILS TO CAPTURE VIEW, BREEZE & SUNLIGHT HOUSE DESIGNED ALL ON ONE LEVEL, LITTLE VARIATION IN ROOF FORM AIR FLOW IMPEDED BY RETAINING WALLS BREEZE NATURAL GROUND LEVEL NO VIEW LEVEL CHANGE AT SIDE BOUNDARY WITH RETAINING WALL GROUND WATER PRESSURE ON RETAINING WALL SIDE SLOPE BENCHING RESULTS IN ENGINEERED STREETSCAPE DOMINATED BY RETAINING WALLS & FENCES SIDE BOUNDARY MORE HOMOGENOUS SLAB ON GROUND BUILT FORM SIDE BOUNDARY MORE CUT AND FILL SIDE BOUNDARY GOOD OPPORTUNITY FOR SIDE BOUNDARY LANDSCAPE GOOD AIR FLOW BETWEEN LOTS UPPER LEVEL BALCONY TO CAPTURES VIEW, BREEZE & SUNLIGHT GARAGE TO LOWER LEVEL WITH LIVING SPACE AND BALCONY ABOVE VARYING ROOF FORM PROVIDES GOOD INTERNAL VOLUME VIEW LEVEL CHANGE WITHIN BUILDING DESIGN STEPPING BUILDING FORM MORE NATURAL APPEARANCE TO STREETSCAPE MORE INTERESTING BUILDING FORMS WHICH STEP WITH LANDFORM LESS CUT AND FILL Diagram - Two Approaches to Sloping Sites Bark Architects Saville Isaacs Glen Petersen Architects Sparks Architects Low ground modification approaches to sloping sites 32

33 Designing to Sloping Sites Your feedback is sought Do you think housing should be chosen or designed to suit the slope of the site or do you think the slope should be re-contoured to suit the house? SLOPING SITE RULES OF THUMB ;; Get a survey to accurately plot the contours and determine the slope of your block. ;; Single slab on ground construction is only really appropriate up to a slope incline of 6 0 or 1:9.5 as the cut/fill required becomes excessive (over 1.5m); ;; On slopes of (up to 1:5) think about stepping two or more slabs or using part slab / part platform construction. ;; On slopes over (1:5-1:3) look at suspended or platform construction which steps with the site. ;; Slopes over 18 0 (1:3) are difficult sites to build on. Look at suspended or pole construction. ;; Look at building design which takes the level change within the building rather than at the boundary, which requires retaining walls. ;; The change of level within building design often results in desirable increased ceiling heights over living spaces. ;; Hidden costs of building on sloping sites can include scaffolding hire, additional engineering input, insulation under elevated timber floors and general increased labour costs. ;; Offset these additional construction costs by reducing the amount of floor area you are building or even stage your development to infill the undercroft at a later stage. Can and should housing respond better to slope? The general feedback on the current DCP cut and fill controls is that they are too restrictive and do not enable the types of cut and fill required to build most volume houses, being a standard slab construction house on the increasingly sloping sites in Tweed. The Diagram on page 14 diagrammatically indicates the scale of cut and fill requirements to manage slope above 4-6 degrees (8-10%), considered as the standard maximum as this generally complies with the DCP, and the type of outcome resulting. This diagram also indicates that above a 4 degree slope (8%) it becomes difficult to comply with the DCP cut and fill provisions. The diagram on the facing page illustrates a comparison over an 8 degree slope between site benching, where the level change is taken up at the side boundary, or the alternative, where the level change is incorporated into the building design. The key benefits are providing occupants with access to views, prevailing breezes and greater sunlight access as well as reducing large level changes on the side boundary between dwellings. Avoiding site benching also improves the streetscape amenity with more interesting building forms and greater opportunity for landscaping. The analysis demonstrates that residential development may be achievable on slopes of up to 18 degrees (approximately 32%) given the use of an appropriate structural system. The analysis finds that slopes over 18 degrees may be too difficult to build on without significantly altering the locality s landform and topography or being able to avoid significant amounts of bulk earth works. This would undermine the visual landscape character and soil stability of the natural undulating topography. Similarly, the analysis demonstrates that the standard site benching is not appropriate on slopes greater than 6 degrees and that there are better design solutions for slopes in the moderate range of 6-12 degrees. Your feedback is sought Should the cut and fill maximum allowance be increased? Should the cut and fill maximum requirements be retained? Rather than setting a prescriptive cut and fill requirement that would apply to all sites, would the cut and fill controls be better related to slope gradients and/or construction types? Review of DCP A1 Residential and Tourist Development Code Discussion Paper 2 Sloping Sites - Managing Cut and Fill 33

34 Slope Indicative Building Type Cut and Fill FLAT 0-6 O 8.5m +/- 1.0m 9m MODERATE 8-12 O 9m +/- 2.0m Within building envelope 9m 9m STEEP O 9m Sparks Architects +/- 3.0m Within building envelope 10m EXTREME < 20 O 10m +/- 1.0m 34 Diagram - Relationship between degree of slope and appropriate structure types

35 Appropriate Structure Type Broad residential housing type Single slab on ground No level changes required within building design May be considered for all slope types No Single slab on ground Stepping slab system Split slab system Part slab / part platform system Platform system (suspended post & beam) Pole House Level changes within building design Garage set under protruding decks on up slope sites reduces visual impact On down slopes garage under house may result in steep driveway grades On down slopes a detached garage reduces bulk building form Housing example Cut and Fill Notes 0-2 o Limited site disturbance and good access off street and limited cut and fill or retaining walls required, less than 1.0m 4-6 o Cut and fill up to 1.5m over an elevation length of 14m with some need for battered landscaped beds or retaining walls Retaining walls may be required up to 1.5m A slope of 1:40 is required for drainage 8-12 o (14-21%) Moderate fall of approximately 5m over a 30m site (on an 100 site) Moderate graded access of 1:5.6 up or down from street Over 1.5m cut and fill required with stepping or suspended slabs Often results in half lower storey or undercroft. Often need for battered landscaped beds and/or small retaining walls o (21-25%) Steep fall across site of approximately 7.4m over a 30m site (on a 140 site) Steep graded access up or down from street of approximately 1:4 Cut and fill over 1.5m required with stepped or suspended slabs May require full level change within building envelope Results in need for battered beds and/or retaining walls May be considered for all slope types No single slab on ground Split level design Part slab part platform system Platform system Level changes within building design Garage set under protruding decks on up slope sites reduces visual impact On down slopes garage under house may result in steep driveway grades On down slopes a detached garage reduces bulk building form Saville Isaacs Architects o (1:3.5-1:3.0) Extremely steep fall across the site of approximately 8.6m over a 30m site Steep graded access up or down from the street of approximately 1:3.5 Limited cut and fill appropriate given the resulting retaining walls and extremely limited level areas which could be achieved Relies on balcony areas for open space Full level change within building envelope required Results in battered landscaped beds and/or retaining walls Sparks Architects Appropriate for down slope sites only Pole design Platform system Split level over 18 o extremely steep fall across the site of approximately 9.7m over 30m steep graded access up or down from the street of approximately 1:2.7 Not suited to cut and fill which would require large engineered retaining elements. Review of DCP A1 Residential and Tourist Development Code Discussion Paper 2 Sloping Sites - Managing Cut and Fill 35