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Building study

SERVICES Because of traffic noise from a nearby main road, it was decided to use a heat-reclaim ventilation system. An acoustically lined heat-reclaim unit was designed to fit above the kitchen cupboards.

Usable cupboard space is maximised and no noisy extract fan is required. Ducting runs within the hall ceiling void to supply air to the bedrooms, living room and bathroom. Stale moist air is extracted from the kitchen and bathroom passing the supply air in the heat exchanger, reclaiming waste heat. The high level of air tightness of the building fabric reduces infiltration heat loss. By placing a hot water coil in the supply duct, heating to the flat can be via the ventilation air. The coil is heated by a simple, gas-fired combination boiler. A SAP rating of 110 is achieved with an annual heating and hot water cost of £106.

The services for the flat come to site as part of a pod unit containing the entrance hall, kitchen, bedroom and bathroom. The pods are lifted into place and connected to the mains services, which are distributed via vertical ducts around the site. The services have been carefully detailed to ensure smooth co-ordination on site. The advantages of this form of construction are the speed of erection and the ability to achieve a consistent level of build quality.

STRUCTURE The aim of the CASPAR competition was to develop a model for affordable inner-city housing that could be applied to a wide variety of sites.

Its strategy was to develop a set of architectural and engineering principles and apply them using an innovative but established, prefabricated construction system. The design was continuously measured against a strict cost plan and benchmarked against traditional construction methods. The engineering principles are:

the housing units should stack vertically and use a simple structural system based on loadbearing cross wall construction;

specific features of the site such as slopes, semi basements and external works should be dealt with using traditional construction methods to provide a simple platform for the housing structure; and stairs, walkways, balconies and roofs should be independent of, or clip onto, the main structure.

The Leeds site had some particular difficulties, not least a 6m slope across it and a variable depth of made ground, up to 7m deep in one place. Foundations comprise a mixture of driven piles and strip footings placed directly onto sandstone. The site has been landscaped to minimise the number and height of retaining walls.

The housing units are constructed using a semi-volumetric form of construction with the service cores completely prefabricated. The staircases and walkways are constructed in steel and were erected before the cores and flat-pack living and bedroom units were craned in. The timber structure is based on a tried-and-tested panel system but, at five storeys, it is one of the tallest timber structures in the country. It also incorporates a number of smaller innovations developed by Volumetric.

One of the main concerns regarding the external walkways was fire protection. Half-hour fire protection was obtained by a combination of fire engineering, redundant or continuous structure, and intumescent paint.

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