Spray Foam Insulation vs Roll Insulation Cost Calculator

How this calculator works

This calculator works in ranges rather than single figures, because real quotes, yields and tariffs genuinely vary that much. It starts from typical UK price, output and savings ranges drawn from published 2026 industry guides and official scheme documentation, then scales them by the quantities you enter and adjusts them for each choice you make below. The result is a low-to-high band that a realistic outcome is likely to fall within, not a promise of the figure you will achieve.

Spray foam runs roughly to per square metre applied against to for professionally fitted wool rolls in 2026, and the roll figure includes the labour, since materials alone are to per square metre. Rolls are how the overwhelming majority of UK lofts are insulated, and for a flat, accessible loft floor they remain close to unbeatable on cost per unit of warmth.

Area to insulate (square metres)

Enter the area being treated, priced per square metre installed for both options so the totals compare directly. For roof underside work measure the slope area; for loft floor work measure the floor area, which matches the footprint of the rooms below.

Where you live

Installation labour is not priced uniformly across the UK, with published guides putting London and South East insulation quotes roughly 15 to 25 percent above the national average. Materials are broadly national in price, so the difference sits mostly in labour, access and parking.

What else affects the figures

The comparison turns on geometry and consequences: rolls excel across open horizontal areas and between regular joists, while foam reaches the irregular, the vertical and the leaky, sealing air movement no quilt can stop; but foam on roof timbers now triggers mortgage-lender scrutiny at several major banks, is excluded from ECO4 funding, and costs to to remove when a survey demands it, a set of liabilities no roll has ever carried. Rolls are also reversible, inspectable and DIY-able, three quiet virtues that matter over a house’s life. Where a loft floor is the job, rolls win the sensible-default argument outright; where the roof slope itself must be insulated, rigid boards between rafters offer foam’s location without foam’s lending baggage, and are usually the better answer to the problem foam is marketed for.

Certification, planning and grid connection

If a calculation here prompts a project, Building Regulations Approved Document L is the standard the work should meet, with U-value targets for each element, and installers registered with TrustMark or a competent person scheme can self-certify compliance. Check grant eligibility before paying for anything: ECO4 runs to 31 December 2026 and the Great British Insulation Scheme continues alongside it, both funding measures partly or fully for qualifying households, and domestic insulation carries 0 percent VAT until 31 March 2027 in any case. An EPC assessment before and after larger projects evidences the improvement for future buyers and lenders.