Cavity Trays Ltd, the longest-established company in its specialised field, has drawn attention to the excellent thermal bridging junction details published by Constructive Details Ltd, and is advising how some thermal junctions might be further enhanced. It has identified some advantageous approaches, offering considerable appeal to energy-conscious architects and house builders.

Thermal bridging details are meeting points of materials at which heat loss opportunities must be minimised and protection against damp ingress maximised. The problem with most such junctions is thermal performance can diminish if materials do not provide unpunctuated continuity or any element forming part of a junction becomes wet. Wetness increases thermal conductivity that can adversely affect the intended calculated efficiency. It is when both these conditions are combined – discontinuousness and wetness, that the best of details can be challenged.

Insulation continuity in the cavity is most vulnerable at joints and junctions, so it makes sense to ensure there are no gaps where the insulation abuts reveals, sills and window heads. By discarding the conventionally shaped rectangular closer and substituting one that is L-shaped, these gaps (and importantly the heat-loss paths via them) are blocked. The L-shape is able to wrap and extend across the face of adjoining insulation, and in so doing provides a union and continuity not possible with ordinary closers. Cavity Trays points out the use of closers with L-shaped insulation can be incorporated with numerous junction details depicted within the Thermal Constructive Details handbook.

The external skin of a conventional cavity wall will increase in conductivity when wet and the kiss points (where outer and inner skins get closer) are usually the most affected junctions. By designing insulation gaps out of the equation, the intended thermal performance of a construction detail is more likely to be achieved.

"Ordinary closers do not overlap the cavity insulation so fail to block the heat loss path occurring at the gaps. In contrast L-shaped closers ensure continuity" commented a company spokesman, "so we call them Continuity Closers – the name says it all."

Suggested reading:
The Book of Wise Decisions / Building Details Best Practice Guide 2012 edition, and Protecting the Building Envelope, volume 22.

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