Loft Insulation

Choosing the Right Loft Insulation for Your Home

At County Building Supplies, we supply loft insulation rolls for professional builders, contractors, self-builders and DIY customers. Whether you're insulating a new loft or upgrading existing insulation, installing suitable materials can help reduce heat loss, improve indoor comfort and support better energy efficiency.

Our range includes Knauf Loft Roll 44 Combi Cut mineral wool insulation in 100mm, 150mm and 200mm thicknesses.

100mm vs 150mm vs 200mm Loft Insulation

Choosing the correct thickness depends on the existing insulation, loft construction and required thermal performance.

• 100mm loft insulation: Commonly used as a first layer between ceiling joists or as part of a multi-layer insulation system.
• 150mm loft insulation: Can be used as an additional layer over existing insulation or as part of a specified loft insulation system.
• 200mm loft insulation: Provides greater thermal resistance than thinner rolls of the same material and is commonly used for upgrading loft insulation levels.

Knauf Loft Roll 44 has a declared thermal conductivity of 0.044 W/mK. The overall insulation performance depends on the total thickness and the complete loft construction.

How Much Loft Insulation Do You Need?

To calculate the amount required, measure the length and width of the loft floor to determine the total area in square metres.

County stocks Knauf Loft Roll 44 Combi Cut with the following stated coverage:

• 100mm: 13.89m² per roll
• 150mm: 9.18m² per roll
• 200mm: 6.84m² per roll

For example, a loft measuring 6m x 5m has an area of 30m². Using the 200mm roll, you would need at least five rolls for one layer, allowing additional material where required for cutting waste.

Installing Loft Insulation Between & Over Joists

Mineral wool loft insulation is commonly installed between ceiling joists, with a second layer laid across the joists to reduce heat loss through the timber.

Ensure the insulation fits without unnecessary gaps or excessive compression. Keep required roof ventilation paths clear, and follow the manufacturer's instructions around electrical equipment, recessed lighting and other heat sources.

Where loft boarding is required, use a suitable raised system to avoid compressing the insulation.

Can You Add Loft Insulation Over Existing Insulation?

In many cases, additional loft insulation can be installed over existing material, provided it is dry, in good condition and suitable for retaining.

Before upgrading, check for dampness, condensation, roof leaks and ventilation issues. The appropriate thickness should be based on the existing insulation and the required thermal performance.

Need Advice?

Not sure which loft insulation thickness or quantity you need? Visit your local County Building Supplies branch or contact our team for help choosing suitable insulation materials and checking availability.