Cavity Wall – has it a future in low energy construction?

The cavity wall is an integral part of the UK & Irish construction industry – it accounted for approximately 70% of new housing. To meet new U -Values for building regulations, achieve passive levels of airtightness and to minimise thermal bridging should we abandon the cavity wall in favour of timber frame or externally insulated masonry? There are issues to overcome but what does cavity wall still offer that External Wall Insulation or Timber frame construction does not ?

  • Familiarity to Architects, Engineers, Builders, tradesmen and home-owners
  • Cost
  • Skills
  • Knowledge
  • Lack of certification for newer products

What are the issues?

  • Thermal bridging at Ground, floor, roof, windows and doors.
  • Suitability for achieving airtightness
  • Breatheability
  • Speed of construction

We believe that architects and builders are finding new ways of overcoming the issues with cavity wall construction. We recently worked with Greentec Eco homes on a passive cavity wall construction project that used aerated blocks to minimise thermal bridging at foundation level, teplo ties as part of a 250mm pumped cavity wall, Partel’s Airtight tapes and Membranes to achieve a passive level air change rate of 0.37 ac/h, and innovative treble wallplate detail free from thermal bridging. Manufacturers appear to believe the cavity wall is here to stay with Partel now producing new airtight and plasterable window tapes for UK and Ireland cavity walls .

Many suppliers are now producing insulated foundations suitable for masonry, various types of full fill cavity insulation, and thermally broken wall ties facilitating full fill cavity insulation up to 300mm. A paper by Joseph Little of Joseph Little Architects studies the issues in greater detail and while last updated in 2006 is still worth reading Partial Fill Cavity Walls: Have We Reached the Limits of the Technology?
This paper while identifying the positives and negatives also serves to highlight the changes and solutions that have been developed since 2006. While timber frame and externally insulated masonry may offer advantages in terms of speed, suitability for airtightness, and thermal bridging it is clear that the modified cavity wall has a future as it can compete on price, and has greater flexibility for finishes and cladding and is engrained in construction in Ireland and the UK.

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