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HeidelbergCement in the United Kingdom
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Thermalite® Trenchblock® and Hi-Strength Trenchblock® are ideal blocks for foundation walling below d.p.c level. They combine lightweight construction with added insulation and, as no cavity infill is required, Trenchblocks® provide a saving in both construction time and cost. Other Thermalite® blocks may also be used.


In addition to Thermalite® Trenchblock® and Hi-Strength Trenchblock®, Hi-Strength 7, Party Wall and Shield blocks can also be used as foundation blocks. This is the case where soil and groundwater conditions prevail up to and including Class DS4 sulfate levels, and for Turbo blocks in conditions of Class DS3, both as defined in Table 2 of BRE Special Digest 1.

Typical details
The following typical details illustrate the proper use of Thermalite® blocks below d.p.c. level, and may not be applicable to other manufacturers’ materials.

Thermal insulation
Foundation walls constructed of Thermalite® Trenchblock® provide a high level of thermal resistance. As a consequence, no cold bridging occurs at the intersection of the insulated external wall, the ground floor and the foundation wall.

The ‘Robust Construction Details’ and the BRE Report ‘Thermal insulation: avoiding risks’, illustrate the use of aircrete in foundation walls as a way of limiting thermal bridging. This, in turn, satisfies the thermal insulation requirements of the appropriate regulations.

Thermalite® Trenchblock® foundation walls can also enhance the U-Value of ground floors and reduce the need for additional insulation in the floor construction. This makes them a cost-effective way of complying with the appropriate regulations.

Concrete floor slab edge insulation
The ‘Robust Construction Details’ document requires edge insulation of the slab if the inner leaf fails to achieve a thermal resistance (R) of 0.75m2.K/W. This can be achieved by 100mm or thicker Turbo blocks. For all other non-aircrete block types, additional slab edge insulation will be necessary.