IT TAKES ALL TYPES A TYPOLOGY OF NEW ZEALAND HOUSING STOCK

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1 IT TAKES ALL TYPES A TYPOLOGY OF NEW ZEALAND HOUSING STOCK IAN PAGE & VERNEY RYAN BRANZ Ltd : Beacon Pathway Ltd TYPE OF PAPER Scientific Paper ABSTRACT Improving the sustainable performance of the housing stock is a major task. To encourage suppliers and builders to scale up for the task, data on the size of the potential market is useful. This project quantifies the number of houses by various characteristics. The basic category is the age of construction of the original house. For each age group physical characteristics are identified which affect the ease or otherwise of retrofit of various measures. The types of retrofit being assessed include insulation, double-glazing, heating appliances, solar panels, and wetbacks. The building characteristics that affect retrofit of these measures include existing insulation, floor crawl space, window condition (for replacements), fire places/chimneys (for efficient solid fuel replacements), hot water cylinder age (for possible solar hot water replacements), roof slopes (for solar panels), and other characteristics. The sources of this data are mainly the BRANZ House Condition Surveys (1999 and 2004) 465 and 565 houses respectively, plus the HEEP database. Quotable Value data was used to obtain total numbers by age group, which was modified by the census count. A scoring system was developed for each age group for retrofitability, and house numbers obtained, thereby indicating the most favourable typologies to retrofit. KEYWORDS Housing; Typology; Retrofit; INTRODUCTION Beacon s aspiration is to bring about a significant and substantial improvement in the sustainability of the residential built environment in New Zealand. It recognises that improving the standards of our existing stock is key to meeting that vision. This means retrofitting the vast majority of our poorly performing housing - but not just any sort of retrofitting; It means retrofitting our houses to a High Standard of Sustainability with the best standards of insulation, energy efficient water and space heating, energy efficient lighting, water efficiency and solutions to improve the indoor environmental quality. As part of Beacon s programme of work in this area an analysis of house typology has been undertaken. This work has been informed through a range of research reports (e.g. Ryan et al, 2008; Buckett et al., 2007) as well as input from architecture and retrofit experts. The purpose of the research is to consider whether our model house types in New Zealand that is the house types that dominate our housing stock are amenable to retrofit to meet Beacon s High Standard of Sustainability (HSS) and, if so, what sort of retrofit packages may be required. This paper provides a summary of analysis of New Zealand housing stock typologies and quantification of the numbers in various groups that are considered appropriate for retrofit projects (these are outlined in Table 1 below). It builds on earlier pieces of research that established a housing typology framework for Beacon (Ryan et al, 2008, McChesney et al 2006, Storey et al 2004)). That framework forms the basis of Beacon s advice to consumers, industry and government on how to retrofit existing homes to meet a HSS (Easton, 2006). The research outlined in this paper helps to provide an insight of the scale of the challenge for New Zealand in meeting Beacon s aspirational goal that 90% of New Zealand homes will be sustainable to HSS by The knowledge gained

2 from this segmentation of the housing stock and an understanding of the prevalence by retrofit typology helps to prioritise Beacon s efforts in this area. Table 1: Typology Number Summary Typology summary Numbers as at March 2006 Number of dwelling units (000) Art Mass Multi Multi Mass Multi Multi Total Bungalow Deco housing units units housing Housing units Housing Housing units Villas s-60s Pre s s s post s METHOD The Methodology followed in this research consisted of three main stages: 1) Literature review - to identify previous work on NZ house typology and identify characteristics of the housing stock, and the types of retrofit measures that are commonly used. 2) Database Review Relevant databases were identified and examined for the detail available, including house types, house component details, existing retrofit information, and regional breakdowns. Databases considered included BRANZ House Condition Survey (HCS) (Clark et al, 2005), Quotable Value New Zealand (QVNZ), Household Energy End-use Project (HEEP) (Isaacs et al, 2006), Census of Population and Dwellings (Census), Statistics NZ (SNZ) and Building Consents, Statistics NZ. 3) Typology Number Estimation - Each database was found to contain useful information including top-down and bottom-up information. Census data is the most complete on dwelling stock numbers; QVNZ data provided age profiles which was used to develop the typologies; the BRANZ House Condition Surveys and HEEP data provide good bottom-up data (e.g. types of components and their characteristics); and building consents give a good breakdown of new housing by storey type over the last 20 years. A framework, based on the QVNZ age profiles, was then developed to utilise all of this data. RESULTS - ANALYSIS OF PHYSICAL CHARACTERISTICS The following section outlines the results of the data analysis undertaken to decide if it is feasible and/or necessary to further sub-divide the typologies, or possibly combine the typologies listed in the original schema (Ryan et al., 2008). In this analysis a combination of prevalence and incidence characteristics have been used. Prevalence refers to overall stock numbers in broad categories such as detached houses, multi-units (dwelling units with one or more walls or ceilings/ floors in common with another unit), single or multi-storey, age groups, and location. Incidence is related to particular characteristics of houses such as component characteristics (e.g. low floor clearance, existing insulation, etc.). As a starting point the QVNZ categories are shown in Figure 1, where the most common type is the detached/semi-detached house group. Multi-unit housing numbers become significant from the 1960s. The original Beacon work (Ryan et al., 2008) suggested that the two storey houses are different from the bungalows of the period and may require a separate typology. The QVNZ database indicates 15% of houses have an upper storey (see Figure 2). This is only about 20,000 houses, i.e. 1.5% of the stock, and is therefore not worth having as a separate typology.

3 The next group suggested as an additional typology was the large mass house group, in particular separating out detached from semi-detached. The 1930s houses have been included under both the bungalow and art deco typologies (see Table 2). For the remainder, houses, the semi-detached versus standalone breakdown is not available in the QV data. Likewise the census in that period does not record stand-alone and semi-detached housing numbers separately. So we do not know the relative numbers of detached and semi-detached. These three decades number about 550,000 units, and, if we assume 5% are semi-detached that is about 30,000 units or about 2% of the stock. From observation these semi-detached houses appear similar to detached houses of the same era in terms of roof slope, ground clearance, orientation, and cladding materials, so a separate category is not required. Figure 1: Decade groups by QV type Note: QVNZ data does not include the total stock so the age group breakdown in Figure 1 has been scaled up to census dwelling totals. Figure 2: Upper storey incidence in houses Note: Upper storey incidence in Figure 2 is derived from QVNZ data on site coverage of the building and total floor area. The main changes within the group occur in floor clearance space, roof space, and the incidence of skillion roofs (see Figure 3, Figure 4, and Figure 5). In the 1940s houses the floor clearance is quite low on average and improves through to the 1960s. In contrast the incidence of low roof space increases from the 1950s, similarly for skillion roofs. The 1940s group has a number of

4 flat roof houses (over 25% of houses have some flat roofs, mainly on lean-tos, according to the 2004 HCS), hence its high incidence of poor roof space. Low floor clearances, flat or low roof slopes (say less than 15 degrees), and skillion roofs (i.e. ceiling lining fixed to rafters) are difficult and costly to retrofit. So for the mass housing group of the 1940s could be a separate typology, but the 1950s and 1960s are similar in terms of sub-floor space and roof characteristics, and will have similar retrofit solutions. Figure 3: Incidence of low sub-floor space by decade Figure 4: Low roof space incidence by decade Figure 5: Skillion roof incidence by decade

5 The 1960s to 1970s multi-unit housing group numbers about 130,000 units and the initial typology research (Ryan et al., 2008) suggested they could be sub-divided into one storey and multi-storey typologies. Figure 6 below shows that the multi-storey component is quite low, about 15 20% of all units for the 1960s and 1970s group, or about 20,000 units. Many of these are state rentals, in two or three storey buildings, and are covered by HNZC retrofit programmes. It was decided to have one category only for 1960s and 1970s multi-units. The 1960s to 1970s multi-unit housing group numbers about 130,000 units and the initial typology research (Ryan et al., 2008) suggested they could be sub-divided into one storey and multi-storey typologies. Figure 6 below shows that the multi-storey component is quite low, about 15 20% of all units for the 1960s and 1970s group, or about 20,000 units. Many of these are state rentals, in two or three storey buildings, and are covered by HNZC retrofit programmes. It was decided to have one category only for 1960s and 1970s multi-units. Figure 6: Incidence of upper storeys in multi-unit housing Figure 7: Incidence of chimneys

6 The incidence of chimneys indicates the potential to retrofit with efficient wood or pellet burners. Figure 7 shows that before the 1970s the incidence of fireplaces and chimneys is quite high. For example, in the 1920 cohort 78% of all houses have a chimney and 16 % of these houses have already been flued, leaving 62% of houses with the original chimney/fireplace. In many cases the fireplace will have been blocked off rather than remaining as an open fire, but it may be available for positioning an efficient burner and inserting a steel flue. Note: In Figure 7 empty chimneys are those without retrofitted steel flues. Adding the 2 sets of bars gives the percentage of chimneys for each decade. The physical condition of windows is an indicator of the likelihood of replacement and hence the opportunity to use double-glazing. Figure 8 shows windows in a serious or poor condition, from the 2004 HCS. Generally windows in houses from the 1930s and 1940s have the worst condition. Figure 8: Poor window condition incidence Note: In Figure 8 poor condition is as defined in the HCS report and is the worse two groups on a 5 point condition scale used for assessing components. The condition of the wall cladding gives an indication of the likelihood of its replacement or major repairs, thereby allowing for insulation to be installed. Figure 9 indicates that the 1930s houses have the worst cladding condition, followed by 1910s and 1950s houses. Figure 9: Poor wall cladding condition incidence

7 The next three figures show the amount of ceiling insulation in the three NZS4218 climate zones. This information helps decide which cohorts have poor or nil insulation and need to be retrofitted. Percent 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% Ceiling insulation - Zone Decade starting >100mm 100mm 75mm 50mm None Source: 2004 HCS and HEEP. 301 houses. Figure 10: Ceiling insulation Climate Zone 1 Percent 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% Ceiling insulation - Zone 2 >100mm 100mm 75mm 50mm None Source: 2004 HCS and HEEP. Decade starting 124 houses. Figure 11: Ceiling insulation Climate Zone 2 Percent 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% Ceiling insulation - Zone 3 >100mm 100mm 75mm 50mm None Source: 2004 HCS and HEEP. Decade starting 160 houses. Figure 12: Ceiling insulation Climate Zone 3

8 Note: In Figures 11 and 12 the numbers of houses in the 1900 sample is small at 3 houses each for Zones 2 and 3, and for the 1910 sample is 6 in Zone 2 and 2 houses in Zone 3. Otherwise the sample is at least 8 houses for each decade and zone combination. Similarly, the incidence of timber floor retrofit bulk insulation is low (see Figure 13) with only 32 houses with insulation out of 465 houses in the 2004 survey: 1970(1 house), 1990 (2 houses), otherwise 3 or more houses with insulation. Figure 13: Retrofitted floor insulation Other data available from the HCS includes hot water cylinder ages, which may affect the decision to retrofit solar water heating. Figure 14 indicates that 1960s houses are prime candidates for replacement cylinders, and hence have potential for solar water retrofits. The assumption is the cylinder life is about 30 years but high pressure cylinders and/or low quality water may reduce this period. Figure 14: Hot water cylinder average age COMPONENT CHARACTERISTICS, TYPOLOGY, AND NUMBERS The figures shown in the preceding section represent most of the characteristics that affect the practical ability to retrofit efficiency measures (others are provided in more detail in Page and Fung, 2008). Most of the data is presented by decade rather than particular typologies because of the format

9 of the data. The next task in the research was to utilise this data and to match it with Beacon s developed typology schema (Ryan et. al., 2008). The start point for estimating numbers by typology is the QV database. As it is incomplete it was scaled up to match the housing stock numbers from the census. This total was spread to the age groups using the QV age profile (further detail indicating how this was achieved is provided in Page and Fung, 2008). The age profile was then used to assign the stock to the different house typologies, and the results are shown in Table 2. In the main there is a direct translation from the age cohort to the typology, but some age groups are split between typologies. For example, mass housing is assumed to be 80% of the 1970s cohort. The Beacon typology schema indicated some possible additional typologies: Mass housing to be sub-divided into 2 or 3 groups. Group housing in the 1970s and 1980s. Multi-units 2000s has both low and hi-rise. The first group is large but the previous section indicates it has approximately similar characteristic across the 30 year period (most houses were constructed in the 50s and 60s). The 1940s cohort possibly has fewer favourable characteristics to facilitate retrofitting than the other two decades and the decade is smaller in house numbers compared to the 1950s and 1960s, so it could be considered as a separate typology, numbering about 78,000 houses. However this report keeps the three decades together. The second group, the so-called Group housing (i.e. standardised housing from major builders) is not thought to be significantly different from other housing of that period. The main distinction between the 70s and 80s is the pre and post-1978 insulation requirements and this division is in the table. Multi-units in the 2000s include hi and low rise units and consent data is available on horizontal and vertical attached units which can facilitate a split for this group (see Page and Fung, 2008). Building component characteristics determine what can sensibly be retrofitted. The lower part of Table 2 scores the components for feasibility/ease of retrofit, based on the charts in the previous section. The scoring is on a 0 to 2 scale and the more favourable the particular component characteristic in the age group, the higher the score. For example, large sub-floor clearances in the 1940s to 1960s houses, compared to other age groups, gives these cohorts a high score for ability to fit floor insulation. Each component is given an equal weight (e.g. floor insulation is weighted equally with ceiling retrofit insulation, and chimney space for efficient heaters.) The component scores are added and the higher total scores indicate which typologies are the better ones to retrofit. These are the villas, the 1940s to 1960s mass housing, and the bungalows. DISCUSSION The typologies generally follow the age group decades and the numbers in each age group are known with reasonable accuracy based on QVNZ data. There are two potential approaches for developing retrofit packages. One is to assess each house component for retrofit (i.e. ceiling, sub-floor, windows, chimney space, claddings, hot water system, etc.) and build-up a package for each component, house

10 by house. This has the advantage that the solution is tailor-made for that particular house. The disadvantage is that it is time consuming and without a detailed inspection the owner will not know what can be done for his or her house, nor the cost. Table 2: Typology stock number estimates Initial estimate of typology numbers Number of dwelling units to March Decade Bungalow Art Deco Mass housingmulti-units Mass housing House Multi-units House House Multi-units Total start Villas s-60s s s s post s pre Dwelling unit numbers (000s) (1) Total Component characteristics (2) Pre 1960s multi-unit numbers = 36 0= Unfavourable, 1= Moderate 2 =Favourable Total all dwelling units (000) at 2006 = 1605 Sub-floor clearance Roof space Chimney space Orient/ Windows HW Cylinder age Existing insulation Total (3) (1) Numbers are based on Working Paper Figure 1 age cohort numbers, and QVNZ breakdowns into multi-units and detached housing. (2) Each decade is scored on a 3 point scale for the favourability or otherwise of retrofit of the component. (3) The higher the more favourable the decade is for retrofit. Each component is equally weighted, i.e scores are added. The other approach, adopted in previous Beacon work (Ryan et al., 2008), is to develop the general typologies, to which a package of retrofits is likely to apply. The advantage is that the cost and retrofit features are readily understandable to owners, as they can identify which typology applies to their house. The disadvantage is that there will be some variability within a typology and the complete package of retrofits will not be possible for all houses in that typology. On balance the second approach seems more useful to owners, and where exceptions arise parts of the package can be suitably modified. For example, it is known the amount of ceiling insulation already in place varies within a typology and it may be necessary to have two different insulation thicknesses for each typology, aside from any variation in insulation due to climate zone differences. An attempt to prioritise the retrofits is outlined at the bottom of Table 2. Here each typology was assessed by component for favourability of retrofit. It is an approximate assessment since not all components or potential retrofits are considered. Also, equal weight is given to each retrofit in totalling the score, whereas cost considerations may affect the weights. However, it is encouraging in that it indicates that the largest group, 1940s to 1960s, scores the highest, showing there is good scope to significantly improve the sustainability of the existing housing stock.

11 CONCLUSIONS The typologies developed in the original work (Ryan et. al., 2008) were found to be useful categories for developing packages of retrofits. The largest group is the 1940s to 1960s mass-housing group and generally the characteristics that affect retrofitting are similar across the 30 years, though the house style changes slightly from small rectangular buildings to larger L-shaped floor plans. This group has several favourable characteristics that facilitate retrofits, likewise the villas and the 1920s bungalows. Other typologies will benefit from retrofits but the package of measures may be more constrained than those mentioned, because some of their characteristics are less accommodating for retrofit. A policy implication is that not all typologies are readily retrofitted. There needs to be consistent agreement across NZ on what is practically achievable for the various types of retrofit. Audits will be necessary on the government Heat Smart programme to ensure that the work is performed to a satisfactory standard, particularly on more difficult sites. A further consideration is the cost-benefits of the various retrofit measures and another paper in this conference addresses this (Page 2010). The numbers in each typology are as given in Table 2 and summarised in Table 1. More detail and further regional breakdowns are publically available in the main report Housing typologies Current Stock Prevalence, Report number EN6570/8 for Beacon Pathway Limited. (Page and Fung, 2008). This and other research can be accessed on the Beacon Pathway website: REFERENCES Buckett, N and Burgess, J. (2007) EECA HERS Houseplans, Report EC1390 for EECA Clark S, Jones M, Page I. (2005) New Zealand 2005 House Condition Survey. Study Report 142. BRANZ. Available for download from Easton, L. (2006). Defining the Benchmarks for Beacon s High Standard of Sustainability: Interim Report to Board, November Report PR109. Auckland: Beacon Pathway Limited. Isaacs, N., Camilleri, M., French, L., Pollard, A., Saville-Smith, K., Fraser, R., Rossouw and P., Jowett, J., (2006) Report on the Year 10 Analysis on the Household Energy End-use Project. Report No SR155, BRANZ, Judgeford, New Zealand McChesney I., Phillips M., Amitrano L. (2006). Sustainability options for retrofitting New Zealand houses. Report TE106 for Beacon Pathway Limited. Page I., Fung J. (2008). Housing typologies Current Stock Prevalence. Report number EN6570/8 for Beacon Pathway Limited. Page I (2010). Cost benefits of housing retrofits. Sustainable Building Conference 2010, Wellington. Ryan V, Burgess G, Easton L (2008). New Zealand House Typologies to Inform Energy Retrofits; Beacon Pathway Ltd. Storey J., Page I., van Wyk L., Collins M., Kreil T. (November 2004). Housing retrofit Housing interventions, Stock, and Markets. Report RF1 for Beacon Pathway Limited.