Product Description:

Knauf DriTherm Cavity Slab 37 is a non-combustible, water-repellent glass mineral wool slab for full-fill insulation of external masonry cavity walls. Supplied in 1200 x 455mm slabs across a range of thicknesses, it is built into the cavity as the wall is constructed, on new build housing, extensions, garages, and outbuildings.

Full-fill insulation only works if the cavity is genuinely full, and this is where mineral wool slab has the advantage over rigid board. The slabs are semi-rigid and slightly compressible, so they push tightly against the masonry on both sides, close up around wall ties, and take up the small irregularities in blockwork and mortar squeeze that leave gaps behind a rigid board. Those gaps matter more than their size suggests, as air moving through them carries heat straight past the insulation.

The 37 designation refers to the slab's thermal conductivity of 0.037 W/mK, the standard-performance option in the DriTherm range, with DriTherm 32 available where a tighter U-value has to be met or the cavity is narrower. The slab carries a Euroclass A1 fire classification, the highest available, meaning it makes no contribution to fire, and a water-repellent additive runs through it so that moisture crossing the outer leaf in driving rain is shed rather than absorbed. Build in as the inner leaf rises, fit tightly with no gaps at joints, and keep clear of mortar droppings, which would bridge the cavity.

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