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 at 100mm thick in 1200 x 455mm slabs covering 6.55m² per pack, it is built into the cavity as the wall is constructed, on new build housing, extensions, garages, and outbuildings.

The 37 designation refers to the slab's thermal conductivity of 0.037 W/mK, giving an R-value of around 2.7 m²K/W at 100mm. It is the standard-performance option in the DriTherm range, suited to projects where the U-value can be met comfortably at the cavity width available, with the higher-performing DriTherm 32 used where the target is tighter or the cavity narrower.

The slab carries a Euroclass A1 fire classification, the highest available, meaning it makes no contribution to fire — an increasingly important consideration in external wall construction. A water-repellent additive runs through the slab so that moisture crossing the outer leaf in driving rain is shed rather than absorbed, keeping the insulation dry and its thermal performance intact in exposed positions. Being semi-rigid and slightly compressible, the slabs push tightly against the masonry on both sides, close up around wall ties, and take up the irregularities in blockwork and mortar squeeze that leave air gaps behind a rigid board. 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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