Typical U-values for fully-filled masonry cavity walls

_{Note: The Uvalues have been calculated assuming that all walls are lined with 12.50mm standard plasterboard (0.190W/mK) on dabs on standard blocks with 10mm mortar joints. Wall ties assumed to be stainless steel at 2.5 per m² with a cross-sectional area of no more than 12.5mm² for structural cavities up to 100mmwide. For cavities up to 150mm, the cross-sectional area of wall ties is assumed to be24mm². For cavities greater than 150mm, the cross-sectional area of wall ties is assumed to be 60mm².Air gap correction level is zero. Multiple layers are required for several of the solutions detailed above.}

_Installation

The thickness of DriTherm^® Cavity Slab and the cavity width should be designed to suit the thickness of the proposed insulation material. It is not possible to compress DriTherm^® Cavity Slab during installation because its resilience will be enough to dislodge bricks before the mortar has set.

DriTherm^® Cavity Slab should be kept clean and free from mortar droppings. All joints should be closely butted. Any cutting and fitting should be neatly done and not distort the layers of glass/rock mineral wool which comprise the material. Cavity trays and damp-proof courses (DPC`s) should be installed to ensure that penetrating water is directed only to the outer leaf.

The illustrations below outline technique only, and do not imply that the outer leaf must be built first. Construction practice will vary from site to site. Where design details differ from those illustrated, please do not hesitate to contact Knauf Insulation for any clarification required.

Wall ties

DriTherm^® Cavity Slab is supplied in 1200 x 455mm slabs for use between wall ties at 450mm vertical centres. Standard butterfly, stainless steel wire ties and vertical twist ties are suitable, as are all ties with a positive drip which will penetrate the top edge of the DriTherm^® Cavity Slab halfway across its width. The use of any other type of tie should be referred to Knauf Insulation Technical Services Team. Advice should also be sought from the wall tie manufacturer as to the maximum cavity width for which the use of a specific tie is approved.

Generally, rows of wall ties should be at 450mm vertical spacing and at horizontal spacings of not more than 900mm or as otherwise required by the structure. Where whole rows of ties are at different vertical spacing, DriTherm^® Cavity Slab should be cut to course, allowing an extra 5mm for compression to form close butt joints. Where extra ties are required, e.g., at the side of openings, DriTherm^® Cavity Slab should be cut and fitted carefully around them. When off-cuts of DriTherm^® Cavity Slab are needed, the slabs can be cut with a long-bladed knife or bricklayer’s trowel

Further recommendations

Above, below and beside openings, where cut strips of DriTherm^® Cavity Slab may be needed, particular care should be taken to fit closely and ensure work is clean and free from debris. At the end of the day’s work and during rainy periods, any exposed DriTherm^® Cavity Slabs should be covered. If DriTherm^® Cavity Slab is terminated vertically at an open cavity, a vertical DPC must be fitted up the inside face of the outer leaf to ensure that any mortar droppings on exposed edges do not bridge the cavity.

Problems to avoid

Contact our Technical Support Team