Whinfell Drive, Kendal – Thomas Armstrong (Concrete Blocks Ltd)

The Cumbria-based Housing Association ‘Impact’ adopted  thin joint construction in its Whinfell Drive project at Kendal, which comprises of five highly energy efficient bungalows. The initial specification and design was based on timber-framed construction, which after tenders were submitted turned out to be considerably over budget. At this point, Thomas Armstrong Construction Ltd (which has long standing links with Impact) investigated the potential of using SIM construction. SIM, in this instance, consists of solid Airtec aerated block walls with a rendered external insulation. However, a SIM wall can have a variety of external finishes, including brick, timber cladding or a high pressure laminate board (HPL).

Thin Joint Technology Ltd provided comprehensive construction details for the SIM construction, enabling the designer to reduce thermal bridging, increase air tightness, increase the thermal values of the walls, floors, roof and windows, all of which easily exceed Part L requirements. For this project, the SIM walls comprise 190mm Airtec XL blocks with a Relius external wall insulation consisting of 120mm Neopor insulation.

A detailed costing exercise revealed that:
• SIM construction would have a significantly lower cost (approx. 10-15% saving).
• SIM construction would achieve better U-values than the framed option, assisted by premium aircrete with the exceptional thermal conductivity (Airtec XL - 0.09W/mK).
• SIM construction reduces the construction time by a week.
• No lead in time was required for pre-manufactured units – blocks were available from stock.
• SIM construction would negate the requirement for a solar water heating system (or any type of renewable energy).
• Single-sourcing could be used for all the materials in the external shell.
The SIM construction system is extremely flexible and SAP target requirements were easily achievable. Design criteria for other projects, which may require even lower U-values, can be adapted to suit each particular element of the dwelling. Post Construction analysis has shown that the actual cost was 19% lower than the original tender price using timber frame construction. In addition, the project was completed in less time than that projected for a timber frame scheme. It is also expected that longer term savings will be achievable as a consequence of lower repair and maintenance costs.

The elemental thermal values for the project:
External walls 0.16W/M2K
Floors 0.10W/M2K
Roof 0.11W/M2K
Windows 0.8W/M2K
Thermal bridging 0.4W/M2K
Air permeability 2.3m3/hr/m2