Spray Foam Insulation vs Fibreglass 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 professionally fitted fibreglass roll in 2026, a premium of two to three times, and the gap widens further for DIY fibreglass at to per square metre in materials. For a standard loft floor, fibreglass at 270 mm meets the Building Regulations target for a few hundred pounds in materials, which frames what foam’s premium is actually buying.

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

Foam’s case rests on jobs fibreglass genuinely cannot do: sealing air leakage through complex junctions, insulating the underside of irregular roofs, and conditioning spaces where rolls will not stay put; against that stand the mortgage-lender flags on roof-applied foam, its exclusion from grant schemes, and removal bills of to when a sale stalls, none of which attaches to fibreglass. Fibreglass’s weaknesses, itchiness, slumping if compressed, needing double foam’s thickness, are cheap problems with known answers. The decision most households actually face is a standard loft, and there fibreglass or its mineral wool sibling wins on cost, grants, lending and simplicity; foam is a specialist tool for the minority of jobs shaped like its strengths.

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.