BCI Joists take Beeston eco-house to three levels

Engineered timber joists manufactured by Boise Cascade have been employed to create a fully habitable roof space or third floor, achieving Level 5 of the Code for Sustainable Homes.

Andrew Banks, of Banks Design Architects, has led the project to build the property on a brownfield site in Beeston.

In doing so, he called on Frame Wise Limited, from Mid-Wales, to supply and erect the main structural frame, featuring the Boise BCI joist for constructing both the two upper floor levels, and the roof itself.

The Managing Director of Frame Wise, Mr Simon Orrells, recounts: "This building employs what we term our Twin Wall system which we developed a year ago to meet the new design code.

Its purpose is to make the internal skin completely independent and loadbearing, so that the floor joists sit on it without there being any thermal bridge.

It is then possible to fix the internal vapour barrier up the wall, wrap around the end of the joists and continue on up the inner skin of the first floor wall to achieve excellent airtightness.

"We have worked extensively with Boise on projects in the education sector and naturally chose to use them for the new Twin Wall domestic design solution.

The BCI joists, packed with Isover mineral wool insulation, also form the 365mm deep roof construction which creates the third floor level".

The depth and integrity of the wall construction achieves a U-Value of 0.1 W/m2K, while the air leakage rate is a miserly 1.0 m3/hr/m2.

The building is being finished with a fibreglass reinforced render system over timber battens.

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