Case Study 6 - Innovative Prefabrication, Lifetime Home and Local Sourcing
West of Scotland Housing Association, Mainholm Road, Ayr
| Type: | New build, steel frame, terrace and semi-detached | |||
| Number of units: | 20 | |||
| SAP rating: | 114 | |||
| U-values: | 0.1-0.21 Wm2C roof |
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| 0.17 Wm2C walls | ||||
| 0.23-0.25 Wm2C floor |
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| Fuel costs: | £0.75 pw (predicted) |
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| Works costs: | £875,500 |
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| Unit cost: | £43,750 |
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| Completion date: | September 1999 |
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| Contacts | Client: | West of Scotland Housing Association | Fiona Birse | 0141 553 1413 |
| Architect: | Assist Architects | Monica McGhee | 0141 554 0505 | |
| Builder: | Robinson and Davidson | Alex Steel | 0141 332 8837 |
The site selected was a semi-rural greenfield one on the edge of the town within reasonable distance of local amenities. Despite the awkward shape and confined nature of the site 75% of the dwellings benefit from passive solar gain. The whole development is barrier free and car parking satisfies barrier free requirements. The housing has a traditional mix of 1,2,and 3 bedrooms.
Figure 6.1 Site Plan
Key Features
Resource Conservation
Pre-fabricated construction, local sourcing
Figure 6.2 Steel construction increases efficiency in housing construction.
The housing is uniquely manufactured from galvanised steel panels which make up the walls, floor and roof structure. The partnership formed between the client, the builder and a local steel fabrication plant (Ayrshire Metals ) has helped this housing development to contribute considerably to the local economy. The technology of steel housing has developed since earlier versions in the 1970.s and this system now offers the following advantages:
- faster construction
- accurate sizing which reduces waste
- lightweight for easy handling
- flexible and adaptable system for lifetime homes
- high acoustic and thermal insulation
- fire and insect resistant
- fully recyclable and re-useable
- advanced technology of protecting steel with "self-healing" coating
- "breathing wall" construction allows moisture to escape but with low air leakage rate
Social and Management
Lifetime homes, contractual partnership
Figure 6.3 Solar porches as entrances help reduce air leakage.
Each dwelling is designed to be highly flexible and adaptable over time to allow for disability needs. There is a .knock -out. panel in the bathroom to allow for future fitting of a hoist as well as additional space to allow for wheelchair use. Services have been accommodated in the ceiling void or external wall thickness to allow changes to be made to the layout.
The use of a partnership arrangement from the outset between the client, builder, architect and steel fabricator has resulted in highly constructive management of problems with joint solutions provided. The traditional pitfall of the design and build post tender savings exercise has been avoided.
Other Relevant Aspects
The Site
Shelterbelt, indigenous planting
The site has a continuous row of mature trees which have been both preserved and enhanced with new planting. This provides good shelter for the site from prevailing westerly winds. Existing planting has been maintained where possible and enhanced with indigenous species to promote appropriate biodiversity.
Energy
High insulation, passive ventilation, solar porches, mechanical heat recovery system
Wall insulation: 150 mm Rockwool quilt and 75 mm Flax/Rockwool 'Heraklith' boarding
Roof insulation: 300 mm Rockwool to loft
Floor insulation: 75 mm Jablite polystyrene boarding
Solar porches are single glazed and narrow to prevent their use as another room. They provide an effective draught lobby to the main house and a small amount of pre-heated ventilation.
Exceptionally high insulation levels have been achieved by overcladding the steel frame with insulation boards as well as filling the structural void. Passive ventilation has been used on the 14 houses which have condensing boiler heating systems. In an attempt to overcome traditional oversizing of boilers in relation to well insulated housing, 6 of the houses use a mechanical heat recovery system as an alternative. This has significantly reduced the size of the boiler which is now needed for hot water only.
Costs and Maintenance
Costs for this scheme are within an agreed budget with Scottish Homes and relatively low given the innovative nature of the construction. Considerable space has been gained by increasing the efficiency of the structure. No cavity is required in the wall construction and the flax-covered external insulation board can receive render directly, simplifying much of the detailing.