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Bethnal goes green

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understanding part L - A housing project with walls, floors and roofs constructed of insulated aircrete exceeds the requirements of Part L

Think environmental prototyping; think east London!

Maybe this is not such a non sequitur as it at first appears, if the three trial houses being built for Bethnal Green and Victoria Park Housing Association are anything to go by.

Using Celcon's 'Jämerä' system, this scheme promises to provide better insulation than required by the new Building Regulations Part L1, and a speedier construction period than more conventional build methods.

Situated in Seabright Street E2, this residential project comprises three plots of varying heights that have been finished in different aesthetic treatments: cladding the solid walls with untreated hardwood; finishing in plasticised render; or applying a brick slip cladding system.

The BRE is monitoring the scheme and comparing the construction timescale with a similar traditionally built structure being undertaken in north London, by the same contractor. Both projects started on 14 January. The Celcon shell has taken just four weeks to complete, with full completion anticipated for 7 May, 16 weeks from the start of the trial.

Generally, 350mm blocks weighing 15.2 kg (dry) have been specified below dpc, which will help the edge insulation at the interface between the wall and ground floor. (The blocks weigh 19.8kg at 30 per cent moisture content. ) The suspended ground floor construction comprises reinforced tongue-and-grooved aircrete planks, 250mm deep and 600mm wide, spanning 5.35m at the longest point. The manufacturer insists that these units 'provide exceptional thermal performance even without additional insulating material', although we have not been able to ascertain the uninsulated floor U-values. With 50mm Styrofoam insulation (k-value 0.027) laid above the planks, the floors have U-values between 0.17 and 0.20 W/m The walls - constructed of solid block and with no added insulation - have a finished U-value of 0.32W/m 2Kand provide significant savings in terms of time and labour. Using a single skin wall (with no cavity to consider) and a 'thin joint'mortar system, a lift can be built in a day.

External openings are formed with aircrete lintels to provide thermal continuity within the wall structure and remove the problem usually associated with thermal bridging. Internal surfaces will be finished with thin spray coat plaster, a much quicker application than conventional plaster with a quicker drying time.

To complete the homogeneity of the building, 250mm-deep reinforced aircrete planks form the roof, thus eliminating trussed rafters (or expensive attic trusses/trussed rafters) and maximising the useable space. This roof structure can be overlaid with battens and counter battens, with 50mm mineral quilt loose laid and finished with 'traditional' tiles.

Whatever you think of the architecture, a SAP rating of 100 and easily achievable Part L U-value compliance show why this system has been used for more than 20 years in Scandinavia.

For details, call 020 8943 9349

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