“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)
Although Crown® DriTherm® Cavity Slab has a BBA Certificate (No.
95/3212), Knauf Insulation have gone a step further and
demonstrated their confidence in the product – and, of course,
their manufacturing consistency – by offering a formal guarantee
that covers two vital aspects of its performance: its thermal
conductivity and its water repellency.
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/m<sup>2</sup>K 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
info@knaufinsulation.com quoting ID: KR14804.
® Registered Trademark of Knauf Insulation
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