SUSTAINABLE CONSTRUCTION IN PUBLIC HOUSING DEVELOPMENTS

Transcription

1 SUSTAINABLE CONSTRUCTION IN PUBLIC HOUSING DEVELOPMENTS Connie K.Y. YEUNG 1 and Clarence K.Y. FUNG Hong Kong Housing Authority, Hong Kong 1 connie.yeung@housingauthority.gov.hk, Tel: (852) , Fax: (852)

2 SUSTAINABLE CONSTRUCTION IN PUBLIC HOUSING DEVELOPMENTS ABSTRACT Disposal of public fill at public filling areas and mixed construction waste at sorting facilities or landfills has been the major approach for construction waste management in Hong Kong. Today, we are running out of both reclamation sites and landfill space. There is an acute need to reduce waste generation and strengthen waste management. The Hong Kong Housing Authority (HA) with a sizable annual public housing production has a major role to play. We actively promote waste reduction, reuse and recycling through a package of innovative measures that straddle through the planning/design stage to construction stage under the 3R principle. We adopt design tools like BIM, Carbon Emission Estimation Model and Life Cycle Cost/Life Cycle Assessment. We use modular flat design with prefabricated building elements with no-frills finishes and green materials. We also explore adaptive reuse of old buildings where opportunity arises. During construction, we use BIM to optimise construction activities and use large panel formwork, metal green hoarding, timber from sustainable sources, recycled materials like marine mud, ground-granulated blast furnace slag (GGBS) and excavated rock materials. We establish an inventory base and enable transfer of C&D materials between HA contracts. During demolition, we adopt selective demolition. Demolished precast slabs are reused as hard paving slabs. Furniture/equipment was given to NGOs for reuse. A number of enabling systems are also in place to ensure the above measures are embedded into the operational processes for implementation by our contractors, suppliers and contract teams. They include promulgation of green-ready specifications and design guidelines, certification to ISO 14001, effective procurement strategies, selective tendering procedure, listed contractors to be ISO certified and Performance Assessment Scoring System. We have been staying ahead in the local industry in sustainable construction, and produce 30% less C&D wastes as a result of our efforts. Keywords: Hong Kong Housing Authority; HA; Sustainable construction; ISO BACKGROUND Disposal of public fill 2 at public filling areas and mixed construction waste at sorting facilities or landfills has been the major approach for construction waste management in Hong Kong. Today, we are running out of both reclamation sites and landfill space. With the current trend, our landfills will reach their designated capacities one-by-one by 2 "Construction waste" means any substance, matter or thing which is generated as a result of construction work and abandoned whether or not it has been processed or stockpiled before being abandoned. It is a mixture of surplus materials arising from site clearance, excavation, construction, refurbishment, renovation, demolition and road works. Over 80% of construction waste are inert and are known as public fill. Public fill includes debris, rubble, earth and concrete which is suitable for land reclamation and site formation. 2

3 2019 if not planned for extension 3, and public fill capacity will be depleted in the near future. There is an acute need to reduce waste generation and strengthen waste management at the construction stage. The Housing Authority (HA) with a sizable annual public housing production 4 has a major role to play. 2. HOLISTIC MEASURES TO REDUCE CONSTRUCTION WASTE The HA actively promotes waste reduction and recycling that straddles through planning, design and construction to demolition stage of buildings under the 3R principle i.e. Reduce, Reuse & Recycle. Major measures undertaken are summarised in the following paragraphs PLANNING & DESIGN STAGE Efforts on construction & demolition (C&D) waste reduction are put right from the planning and design stage MODULAR FLAT DESIGN Riding on standard block design and the subsequent site-specific design, Modular Flat Design has been developed since 2008 as our prevailing tool kits for mass customization. It covers a whole spectrum of small modular flats as well as family modular flats. By standardizing the design of structure and fabric components, precasting and prefabrication is enabled, buildability is enhanced and better economies of scale are achieved PRECASTING AND PREFABRICATION As a mandatory construction practice since 1997, precast and prefabricated elements have been widely used in public housing developments. These include precast staircases, facades and beams, partition walls, semi-precast slabs, volumetric precast bathrooms and kitchens. Through production off site under factory environment, high quality building products with less material wastage are resulted NO-FRILLS FINISHES Conscious use of durable and affordable finishes is stipulated in our Model Client Brief for public housing developments, e.g. more extensive use of paint to replace wall tiles, fair-faced concrete with multi-acrylic paint as external wall finishes and skim coat as internal wall finishes inside flats, unpainted staircase railing, and use of green materials such as FSC certified timber etc. Lean use of building materials minimizes wastage during construction and induces fewer burdens in future maintenance and repair. 3 Quoted from the Hong Kong Blueprint For Sustainable Use of Resources published in May 2013 by the Environmental Bureau, HKSAR Government. 4 HA is building an average of about 79,000 new public rental flats for five years from 2012/13 to 2016/17, and geared to achieve a target production of 100,000 flats in five years starting from Since 2011, HA has also resumed Home Ownership Scheme developments producing about 17,000 flats in four years from 2016/17 to 2019/20; and thereafter about 5,000 flats a year. 3

4 BUILDING INFORMATION MODELLING (BIM) BIM effectively produces building design three dimensionally on screen, making it easier to identify and discuss design issues. We have succeeded in optimizing engineering design projects encountering complicated topography and various site constraints, and avoided abortive construction works at subsequent stage LIFE CYCLE ASSESSMENT (LCA)/ LIFE CYCLE COSTING (LCC) AND CARBON EMISSION ESTIMATION (CEE) MODELLING In place since 2005, we make use of the localized LCA/LCC computer model to make cost and environmental comparisons on new or alternative materials for residential buildings on a life cycle basis to enhance sustainable solutions. Since 2011, we have further developed a user-friendly CEE methodology to holistically evaluate the carbon emission of our new public housing developments throughout the building life cycle, to ensure these designs are optimized by comparing against the benchmarking estates 5. The CEE model embraces the carbon emission from major construction materials and building operations as well as the carbon reduction from renewable energy systems and absorption from tree planting ADAPTIVE REUSE OF OLD BUILDINGS Adaptive reuse of old buildings is also explored where opportunity arises to save their historic and cultural values as opposed to demolition. Successful cases include conversion of the former Shek Kip Mei flatted factory into a Jockey Club Creative Arts Centre and adaptive reuse of the historic Mei Ho House, conservation of the Pavilion and the Little White Shed in the redevelopment of So Uk Estate, and conversion of Chai Wan flatted factory to a new public rental housing development CONSTRUCTION STAGE We have been staying ahead in the local industry in advancement of sustainable construction. Major measures include LARGE PANEL FORMWORK & METAL HOARDING To reduce the use of timber in temporary works, we adopt mechanized construction using metal large panel formwork and metal hoarding that allow repetitive use and recycling at end of life. Since 2011, we have specified the use of timber from sustainable sources only for all temporary works BIM BIM is again employed to optimize construction activities, facilitate coordination amongst work trades, detect and avoid clashes of utilities and building services with building structures, hence minimise abortive work on site. 5 The carbon emission benchmark of our typical New Harmony One block stands at kg CO 2/m 2 Gross Floor Area. Through continuous effort in progressive implementation of energy saving measures, HA has achieved a substantial reduction in annual electricity consumption in communal areas within new public housing developments by 42% (from 1,032 kwh to 536 kwh per flat) over the past 11 years from 2000/01 to 2011/12. 4

5 MODULAR HOARDING AND GREEN HOARDING Modular hoarding adopts an innovative erection method where typical hoarding modules are formed by connecting steel members through the use of bolts and nuts in fabrication yard and then delivered to the public pavement and fixed on top of precast concrete footings. Not only all the steel hoarding members and concrete footings can be demounted for reuse in the next construction contract, it causes fewer disturbances to pedestrians during erection and dismantling. Reusable and demountable green hoarding in the form of large vertical green panels on the other hand provides added benefits as dust and visual screens during construction, and has been reused as permanent fence wall in a pilot project TRANSFER OF C&D MATERIALS We have established an inventory since 2010 giving details of quantities of C&D materials available from each site for export to other HA projects for reuse. The inventory is made available to all HA s contractors to facilitate bulk transfer of C&D materials between HA s contracts. Enabling over twenty numbers of successful transfers between contracts, an estimated amount of over 80,000 tones of C&D waste has since been reduced USE OF RECYCLED MATERIALS This includes cement-stabilised marine mud recycled for backfilling and making masonry blocks, pavers and roof tiles; glass and broken concrete debris generated from demolition works recycled as aggregates for paving blocks; bore-logs from G.I. works recycled as planter kerbs; Ground Granulated Blastfurnace Slag (GGBS) reused to partially replace cement in precast concrete construction; and excavated rock materials recycled for construction of footing of site hoarding and for construction of gabion structures DEMOLITION STAGE Efforts on C&D waste reduction continue down to demolition stage. Major measures include PROLONGED SERVICE LIFE OF BUILDING Reduction of C&D waste is just a part of our bigger picture of sustainable procurement in HA s practices. Through incremental enhancement of design and construction control, the service life of our residential building structures completed after 1992 is at least 100 years. It defers the need for demolition of buildings SELECTIVE DEMOLITION Selective demolition can be considered as a reverse construction process. It refers to a systematic way to demolish a structure such that re-usable items are selectively and systematically taken down in a way suitable for removal off site for re-use or recycle. All fixtures, electrical appliances including air-conditioners and lose furniture can be identified and removed for salvaging or recycling. The remaining concrete structure is then demolished and delivered to the recycling plant as the raw material for production of recycled aggregates. In demolition of Lower Ngau Tau Kok Phases 2, 3 and 5, old 5

6 furniture/ equipment are salvaged for NGO s reuse, and demolished precast slabs are reused as hard paving slabs in the demolition contract. 3. ENABLING SYSTEMS TO ACHIEVE RESULTS A number of enabling systems are also in place to ensure the above measures are embedded into the operational processes for implementation by our contractors, suppliers and contract teams. They include PERFORMANCE-BASED SELECTION MECHANISM OF CONTRACTORS A performance-based selection mechanism is introduced to secure competent and reliable business partners to undertake our works contracts, in gist as follows- (a) Our List Management maintains HA's permanent lists of works contractors; (b) Our Performance Assessment Scoring System (PASS) provides a performance monitoring system with objective scores for contractors, inclusive of their environmental site performance; (c) A selective tendering procedure is adopted in the selection of tenderers using PASS scores where applicable; and (d) During tender evaluation, we apply performance scores, corporate scores and price scores in tender assessment ISO CERTIFICATION ISO specifies the use of processes, practices, materials or products that avoid, reduce or control pollution to minimize its impact on the environment. HA has achieved ISO certification in June 2009 which demonstrates our commitment s towards environmental excellence. HA s listed contractors also required to be ISO certified. Moving forward, we initiate to implement ISO requirement for manufacturers of our major building materials in phases to ensure a holistic sustainable framework is implanted into the entire supply chain GREEN-READY SPECIFICATIONS Specifications requirement on sustainable construction have been incrementally introduced into our works contracts. These include submission of waste management plan by contractors since 2000 and environmental management plan since 2002; mandatory provision of water recycling facilities to recycle waste water for wheel washing & duct suppression, hard paved construction to achieve clean and safe site environment and proper material storage area hence minimizing handling wastage, and weighbridge to check the weight of dump trucks leaving HA sites all since The Integrated Pay for Safety, Environment and Hygiene Scheme which is an incentive-based pay scheme towards a safe environment and better site hygiene has been in operation since The latest changes in 2012 include mandatory provisions of Environmental Manager and Environmental Supervisor to strengthen good on-site management and provision of incentives for extra-mile achievements on environmental and hygiene culture and innovations. 6

7 4. PERFORMANCE INDICATORS & WAY FORWARD We have been staying ahead in the local industry in sustainable construction, and are (a) producing 30% 6 less C&D wastes as a result of our efforts; (b) building 41-51% 7 less costly than that of private residential buildings of average standard in Hong Kong; and (c) having 80% 8 less accident rates than the norm in Hong Kong. We will continue to excel our sustainable construction by way of- (a) undertaking research and development activities as part of our design and project management routine, (b) by regular liaison with our business partners to encourage innovative and creative ideas, (c) by vigorous experience sharing with industry stakeholders both local and overseas, and (d) taking on board advanced construction practices when deemed smart and practicable. 5. REFERENCES Fung, Ada et al, Planning, Design, and Delivery of Quality Public Housing in the New Millennium Cheng, I. et al, A Roadmap for Site Safety in the Construction of Public Housing in Hong Kong, paper presented at the HKU-HKHA International Conference 2013, Hong Kong, 2-3 May. 6 Based on a research conducted by the Hong Kong Polytechnic University on Construction Waste Management in Building and Demolition Contracts of Housing Authority (HA), a typical HA building contract generates 0.176m 3 /m 2 Gross Floor Area of construction wastes, which is 30% less than a private sector residential project that generates 0.250m 3 /m 2 Gross Floor Area. 7 Based on a recent review on Cost Effectiveness of the Superstructure of HA Domestic Blocks conducted by the Hong Kong Housing Authority in June 2013, the superstructure construction cost of HA's domestic buildings is on the average 41-51% lower than that of residential buildings of average standard in the private sector at 2012 second quarter price level. 8 The accident rate per 1,000 workers on HA s new works construction sites, a reactive indicator, has been considerably lower than the industry average. For the former, the accident rate for 2009, 2010, 2011 & 2012 is 9.4, 9.9, 9.0 & 7.4 respectively. For the latter, the accident rate for 2009, 2010, 2011 & 2012 is 54.6, 52.1, 49.7 & 44.3 respectively. 7