Updated
March 27, 2026
Reviewed against the current calculator logic, structured content, and internal linking used on BuildCostLab.
Insulation Estimating
Work out how much loft insulation to buy before you order
This page explains the main checks to make before turning a simple coverage figure into a real order quantity.
Methodology
Planning-first estimate
Use this guide to build a rough material estimate, then confirm it against product coverage data, site conditions, and supplier pack sizes before you order.
Trust
How we publish
See the calculator methodology and editorial policy for the standards behind these pages.
Use the calculator first
The quickest path is to start with Loft Insulation Calculator, then use this guide to sense-check the result and decide what to buy next.
Why this page exists
Best for early thermal upgrade planning, material comparisons, and checking how many packs or rolls a room, floor, roof, or partition is likely to need.
Core assumption
Insulation estimates usually depend on covered area, product thickness, and the fact that boards and rolls are bought to pack coverage, not to neat geometry alone.
Common mistake
The biggest mistakes are confusing thermal thickness with coverage, ignoring cut loss around framing or rafters, and overlooking staggered joints or offcuts.
Next step links
Open the full Insulation Estimating cluster or go straight to the Loft Insulation Calculator.