Knauf Insulation guarantees that each Crown® DriTherm® Cavity Slab supplied by us to you has been manufactured so as to be resistant to the passage of water from the outer leaf to the inner leaf… and to have a thermal conductivity of 0.035 to 0.037 W/mK… and that such properties shall remain effective for a period of 50-years from the date of this Guarantee*...” (Quote)
Masonry cavity walls have been popular since the 1920s and are now the most widely used form of external wall construction in the UK and Ireland. It’s a simple, easily understood method that allows scope for design flexibility and, when the cavity is used for insulation, one that can offer very high levels of thermal insulation.
The maximum allowable Elemental U-value for external walls varies: 0.35 W/m2K in England, Wales and Northern Ireland and 0.27 W/m2K in Scotland and Ireland, and, not surprisingly, how these target values are achieved depends on both the methods and materials used in their construction. The most effective method of insulating an external
cavity wall is with full fill cavity insulation as, apart from giving the best U-value-to-wall-width ratio, it’s also the lowest in cost. But a number of statutory regulations – for example, NHBC standards – prevent full fill cavity insulation being used in some types of building and determine which method has to be used.
Crown® DriTherm® Cavity Slab is a lightweight, semi-rigid slab of glass mineral wool designed specifically for use in both partial fill and full fill cavity wall insulation systems. Measuring 1200mm long by 455mm wide – for use with wall ties at a vertical spacing of 450mm – it’s available in five thicknesses from 50 to 100mm with thermal conductivities ranging from 0.035 to 0.037 W/mK. The popular 75mm thick slab is supplemented by Crown® DriTherm® Cavity Slab Plus: its thermal conductivity of 0.036 W/mK giving it a higher thermal resistance than its equivalent in the ‘standard’ range.
Moisture resistance is achieved using a water repellent, silicone binder that ensures no liquid water can pass through the slab from the outer to the inner leaf of masonry. Nor will it transmit moisture by capillary action and, as the BBA Certificate states, it can “…therefore be used in situations where it bridges the damp-proof courses of the inner and outer leaf.” But, despite its water repellency, Crown® DriTherm® Cavity Slab offers no resistance to water vapour allowing it to pass freely and the structure to breathe.
It’s a winner all round – you’ve Knauf’s promise!
*Of course, some ‘Terms & Conditions’ apply! For details about these, Knauf Insulation’s products or to obtain copies of their literature, please call 08700 668 660 or e-mail firstname.lastname@example.org quoting ID: KR14804.
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