How Much Loft Insulation Do I Need?
Working out how much loft insulation you need starts with the area being insulated and the insulation thickness required.
Different products cover different areas, so the number of rolls required depends on the exact insulation product as well as the size of the loft.
Advice by Andrew Tsaroulla, Director of TSAR Building Supplies
Last updated: 10th October 2026
Measure the Loft Area
Measure the length and width of the area being insulated.
Multiply the two measurements to estimate the area in square metres:
Length × Width = approximate floor area in m²
For irregular lofts, divide the space into smaller sections and calculate them separately.
Check the Required Insulation Thickness
The amount required is not only determined by floor area.
You also need to know:
Required insulation depth
Whether one or more layers are being installed
Whether insulation is already present
The type of insulation being used
Check the Product Coverage
Different insulation rolls cover different areas.
TSAR supplies loft insulation products from manufacturers including Superglass and Knauf, with individual product coverage shown within the insulation range.
How to Calculate the Number of Rolls
Divide the area you need to insulate by the coverage shown on the chosen roll, then round up to a whole roll.
For example, if one layer covers 40m² and each roll covers 8m²:
40 ÷ 8 = 5 rolls for that layer.
If another layer is required, calculate it separately using the coverage of the product chosen for that layer. Rolls of different thicknesses can cover different areas.
This example assumes no cutting waste. Allow for the layout of your loft and any additional material needed before placing your order.
Consider the Loft Layout
Joists, corners, hatches and areas that are difficult to access can affect the amount required.
Measure the usable area carefully before ordering rather than relying solely on the overall property dimensions.
What Loft Insulation Does TSAR Supply?
TSAR supplies loft insulation rolls from Superglass and Knauf in a range of thicknesses.
Check the coverage per roll for the exact product and thickness you need. If you are adding to existing insulation, confirm the required additional depth and whether the existing material is suitable to retain.
Send us the area to be insulated, the specified product or thickness and your delivery postcode so we can help you check quantities and availability.
Related Building Advice
What Thickness of Loft Insulation Should I Use? →
Rockwool vs PIR Insulation →
Need Loft Insulation?
Send TSAR the approximate area, required product or thickness and your delivery postcode.
General guidance only: Insulation requirements can vary according to the building, construction and applicable project requirements.