Insulation · Project planning

Loft Insulation Calculator

Calculate a metric top-up from existing depth, target depth and the thickness and coverage of new rolls. First-layer and cross-layer surfaces can be recorded separately.

By Alish Gautam, Software Developer · Updated · Calculation methodology

Start with the editable example below. Dimensions retain their physical size when units change. Region sets currency labels without converting currencies; confirm entered quotes after changing region. Thermal inputs labeled US R retain that unit in every region.

Measured insulation surfaces

Use non-overlapping rectangles. Enter openings as area on the surface they interrupt.

Room / surface 1
Basic settings
Choose the estimating method.
Product settings
Product and system dimensions
Editable arithmetic example. Replace with your project or product specification.
Editable arithmetic example. Replace with your project or product specification.
Editable arithmetic example. Replace with your project or product specification.
Editable arithmetic example. Replace with your project or product specification.
Optional supplier product name, chart revision or quote reference, saved in shared project state.
Advanced settings
Advanced planning settings
Planning allowance, not a code or industry requirement. Set zero to order the exact rounded takeoff.
Cost settings · GBP
Optional quote prices
Optional supplier quote in the selected currency. Blank omits cost.

Project takeoff

Whole packages round up. Allowance is separate from purchased surplus. Prices omit labor, delivery, tax and other items unless explicitly entered.

Gross measured area
80 m²
Opening / exclusion deductions
0 m²
Top-up depth
200 mm
Whole additional layers
2
Finished depth with whole layers
300 mm
Rolls per layer
9
Total rolls to buy
18

Supplier-ready material list

Rolls
18
Geometry / layout breakdown
Dimensions use the selected measurement system.
SurfaceMaterialGross (m²)Net (m²)
Room / surface 1floor8080

The commonly cited 270 mm figure is not preset as a verified current requirement. Whole-element thermal performance and applicable UK jurisdiction determine compliance.

How it works

Top-up = max(0, target − existing). Whole new layers = ceil(top-up / roll thickness); rolls round per layer.

Assumptions and limitations

The commonly cited 270 mm figure is not preset as a verified current requirement. Whole-element thermal performance and applicable UK jurisdiction determine compliance.

Whole packages round upward after the chosen allowance. Physical geometry and purchase reserve are separate. Manufacturer and project specifications override editable examples; the selected region does not establish a local code requirement.

Sources and boundaries

Energy Saving Trust: Roof and Loft Insulation

Open the source · Web guidance; edition not stated · Reference checked 2026-10-04

Scope: Homeowner loft retrofit advice

Used for: Loft floor versus roof strategy; Access and storage considerations.

Does not establish: Building Regulations compliance from depth alone; Unverified 270 mm product prescription.

Current page text was checked. It did not independently expose the 270 mm value; the tool uses a custom depth example rather than claiming that value as a current rule.

UK Government: Conservation of Fuel and Power: Approved Document L

Open the source · 2026 and earlier applicable editions · Reference checked 2026-10-04

Scope: England regulatory guidance and edition applicability

Used for: 2026 edition and earlier-edition transition context.

Does not establish: A single UK-wide target; Automatic compliance from loft depth.

The listing includes 2026 guidance and earlier editions. Applicable standards depend on project transition arrangements and jurisdiction.