Wednesday, February 16, 2011

Passive House Foundation Systems

Last week we looked at some of the different types of foundation systems being used in the design and construction of passive houses in Ireland and the UK. According to the current 2008 Technical Guidance Document Part L, the recommended average elemental U-value for ground floors is 0.25W/(m2K) for floors with no underfloor heating (UFH) and 0.15W/(m2K) for floors with UFH. The first value is due to go down to 0.21W/(m2K) with the implementation of the 2010 revision in the near future. So we can see that the building standards are moving towards the passive house standard of between 0.10 to 0.15 W/(m2K) for ground floors. Interestingly, Viking Homes discusses the effects of cold bridging for floors designed to meet the 0.25W/(m2K) target and how the actual figure can be considerably higher (see below).

This reinforces the passive house approach of providing a continuous thermal envelope with excellent airtightness and minimal thermal bridging. The Department of the Environment, Heritage and Local Government has provided some guidance on this with the publication of the Acceptable Construction Details and airtightness and insulation continuity guidelines. This focus has promoted some innovative approaches to foundation designs from Viking Homes, Aeroboard, Passive House Builders and the Green Building Store in the UK (see video below).