Scheme Summary

The Brookes is a social housing scheme comprising ten 2, 3 and 4 bed family homes for rent. These are built to standard North British Housing designs using Greenframe timber frame construction. Completed 1999.


Scheme Details

TNBH's usual practice has been to develop a standardised house design package using traditional masonry construction. This has evolved over several years in response to detailed resident surveys, technical and cost audits and life-cycle cost analysis. In 1998, as part of its commitment to provide more sustainable housing solutions, the North British Group together with a local developer set up a joint venture company called Greenframe to manufacture sustainable timber frame housing.

Greenframe has a training partnership with Huddersfield Technical College's centre of excellence for construction skills. The company is planning to move from its factory in Huddersfield to a larger site in Dewsbury (June 2001) where it will manufacture up to 16 houses per week.

The Brookes was one of the first projects by NBH to use the Greenframe system.


Environmental Features

The Greenframe system includes factory manufactured panels using sustainable sources of UK grown timber, together with sheet materials manufactured from UK timber waste and forest thinnings. This ensures that the embodied energy in the frame is kept low and supports employment and sustainable forestry in the UK.

High levels of insulation have been incorporated with 89mm of cellulose insulation (recycled newspaper) between the frame studs and 100mm of mineral wool batts between the timber frame and the brick cladding. The roof space incorporates 300mm of blown cellulose.

Thermographic imaging has proved the integrity of the insulation and airtightness pressure testing achieved values better than 4 air changes per hour @ 50pa. pressure.

Windows have been glazed with low emissivity argon filled double glazed sealed units. A local decision based on perceptions of maintenance costs was taken to include PVCu frames. NBH's usual practice is to specify high performance softwood.

The Brookes was also part of an initiative with local heating and ventilation equipment manufacturer Baxi, to develop a more appropriate heating system for low heat demand housing. The insulation and airtightness of the houses gives a very small heating load of around 2kW. It can be problematic to heat this type of house efficiently with a conventional wet system; the smallest available gas fired boiler has an output of 6kW.

The Baxi system, piloted on 3 of the houses, contains a mechanical ventilation and heat recovery system that is 90% efficient. Heat is added to the ventilation airflow instead of using radiators. A small conventional boiler is used as a heat source with the heat for space heating and domestic hot water held in a thermal store. The system has the added benefit of providing a constant supply of filtered fresh air.


Costs

The original cost model for the project was based on masonry construction and NBH's standard performance specification. The decisions to use a highly insulated frame and to incorporate the Baxi MVHR system resulted in additional scheme costs of 10,000. The overall scheme cost was 568,570 and the average cost per unit is 57,360.

The potential cost savings resulting from the use of a timber frame were not realised on this project. The contractor was unfamiliar with timber frame and was unprepared for the programme savings that became apparent. It is NBH's intention to work with this contractor on another project to mutually benefit from the experiences gained on The Brookes, particularly with regard to construction time and the consequent savings in overhead costs.


Developer's Comments

The project is being closely monitored for technical and resident views. Data analysis from the first year of occupation will take place in March 2001. Current indications are that the residents are very satisfied with their homes.

Social and economic sustainability was addressed on this project. The local community was consulted on the project and is aware of the environmental objectives being pursued. The local school has studied the project, visiting the site to watch the progress. Greenframe is developing its training partnership with Huddersfield Technical College and has created 16 jobs in its new factory in Dewsbury.

The successful use of Greenframe is contributing to the expansion of this environmental friendly form of construction both within NBH and to external clients.

The use of the prototype Baxi heating system and the absence of radiators was initially considered a risk in terms of social acceptability and performance. However, the residents see the lack of radiators as an advantage as living spaces are more flexible. Any performance problems concern over-heating rather than lack of heat.

Baxi plan to develop a consumer orientated integrated product incorporating purpose made components as a result of this project.

Contact: Gordon Snape,
Crown Green Works,
Calder Wharf,
Huddersfield,
Nr Ravensthorpe,
WF13 3JW

Websites:
www.nbh.co.uk