Spray Foam Insulation vs Rockwool 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 costs roughly to per square metre applied against to for fitted stone mineral wool in 2026, so a typical loft in foam runs to where wool does the job for to . Foam’s advantages are real, speed, airtightness and reach into irregular gaps, but they now come attached to a liability wool does not carry.

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 deciding factor for most homeowners is no longer price but lending: several major UK mortgage lenders flag properties with spray foam on the roof timbers because cured foam hides the timber condition surveyors must inspect, RICS guidance reflects the same concern, and removal costs to when a sale or remortgage stalls, while spray foam is also excluded from ECO4 grant funding. ROCKWOOL carries none of this: it is non-combustible with the best fire rating going, acoustically excellent, removable, inspectable, and its performance per pound across a loft floor is unbeatable, which is why our honest guidance is wool for any standard loft and foam only for specific problems, applied over a membrane by a BBA-certified installer with paperwork you keep forever.

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.