Cavity Insulation

Choosing the Right Cavity Wall Insulation for Your Project

At County Building Supplies, we supply cavity wall insulation for professional builders, contractors, self-builders and DIY customers. Whether you're constructing a new property or upgrading a suitable cavity wall, choosing the correct insulation can help reduce heat loss, improve energy efficiency and support compliance with Building Regulations.

Our range includes Knauf DriTherm mineral wool cavity slabs and Mannok rigid cavity insulation boards in a selection of thicknesses.

Mineral Wool vs PIR Cavity Insulation

Mineral wool and PIR insulation are both used in cavity wall construction, but they offer different characteristics.

• Mineral wool cavity slabs: Designed for suitable masonry cavity walls, mineral wool insulation provides thermal resistance and can accommodate minor irregularities in masonry. County stocks Knauf DriTherm 32 and DriTherm 37 slabs in selected thicknesses.
• PIR cavity insulation boards: Rigid boards offering high thermal resistance relative to their thickness. County stocks Mannok Therm Cavity MC PIR insulation boards for compatible cavity wall applications.

The correct product depends on the wall construction, cavity width, required thermal performance and whether the design uses full-fill or partial-fill insulation.

Knauf DriTherm 32 vs DriTherm 37

Knauf DriTherm 32 and DriTherm 37 are mineral wool cavity insulation products with different thermal conductivity values.

DriTherm 32 has a declared thermal conductivity of 0.032 W/mK, while DriTherm 37 has a declared value of 0.037 W/mK. A lower lambda value indicates better thermal resistance at the same thickness.

County stocks DriTherm 32 in 100mm, 125mm and 150mm thicknesses, alongside DriTherm 37 in 50mm, 75mm and 100mm thicknesses.

Choosing the Correct Cavity Insulation Thickness

The required insulation thickness depends on the cavity width, wall design, insulation material and target U-value.

When comparing products, consider both the insulation's thermal conductivity (lambda value) and its thickness. The thermal performance of the complete wall also depends on the masonry, wall ties, junctions and installation quality.

Always check the manufacturer's technical guidance and the applicable Building Regulations before selecting insulation for a new build or renovation.

Full-Fill vs Partial-Fill Cavity Insulation

Full-fill cavity insulation is designed to occupy the specified cavity space in suitable wall constructions, while partial-fill insulation leaves a residual cavity as required by the wall design.

The correct approach depends on the product specification, masonry construction, exposure to wind-driven rain and other design requirements. Not every insulation product is suitable for both methods.

How Much Cavity Insulation Do You Need?

Measure the length and height of the walls requiring insulation to calculate the total area in square metres. Subtract window and door openings where appropriate, then allow for cutting waste.

For example, a wall measuring 8m long by 2.5m high has a gross area of 20m². Compare the required area with the stated coverage per pack or board.

County's Knauf DriTherm products are listed with different pack coverages, so check the individual product details before ordering.

Need Advice?

Not sure which cavity insulation type or thickness you need? Visit your local County Building Supplies branch or contact our team for help with product information, quantities and availability.