How this calculator works
Rolls = round up[(area x waste factor) / coverage per roll].
Worked example
A 6 m x 4 m loft (24 m2, 5% waste = 25.2 m2) with a roll rated at 5.5 m2 coverage needs 5 rolls.
Assumptions to check
- Coverage per roll is taken from the pack (it already reflects the rated depth/R-value/U-value) rather than a plain area figure, since the same roll length covers less area at a greater installed depth.
- Joists, hatches, pipework, and cross-layering (laying a second layer perpendicular to the first) are not modeled - add extra rolls for a second layer.
- Loft insulation depth and material recommendations vary by region and building regulation; use the coverage stated for your chosen product and target depth.