PIR Insulation Board 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.

PIR board costs roughly to per square metre at 100 mm for supply in 2026, with thinner and thicker sheets scaling roughly by volume, and fitted prices running to per square metre depending on the application. PIR, polyisocyanurate, is the workhorse of high-performance insulation with a thermal conductivity around 0.022 W/mK, meaning it hits a given target in roughly half the thickness mineral wool needs, which is why it dominates rafter, floor and dot-and-dab wall applications where space is tight.

Area to insulate (square metres)

Enter the area to be covered in boards. Standard PIR sheets are 2.4 by 1.2 metres, covering 2.88 square metres each, so 30 square metres is roughly 11 boards allowing for cuts and waste of around 10 percent.

Board thickness

Rigid insulation is priced largely by volume, so thickness moves the per square metre cost almost linearly: 50 mm boards cost roughly 60 percent of the 100 mm price and 150 mm around 40 percent more. The thickness you need depends on the U-value target for the element under Building Regulations Approved Document L and the material’s thermal conductivity, which is why higher-performing boards can hit the same target with less depth.

Supply or fitted

Boards themselves are the smaller half of a fitted price: cutting, fixing, foaming gaps and taping joints roughly doubles the supply cost or more, depending on the application, with fiddly rafter work at the top and open floor areas at the bottom. PIR is workable for competent DIYers with a fine saw and foil tape, and getting the joints taped airtight matters as much as the thickness, since gaps leak a disproportionate share of the heat.

What else affects the figures

Brand matters less than certification: Celotex, Kingspan Thermafloor and TF70, Recticel, EcoTherm and Unilin all make BBA-certified PIR of near-identical performance, so merchants’ prices for the same thickness are directly comparable, and prices move meaningfully with chemical feedstock costs, making it worth checking two or three merchants for live pricing. PIR’s weaknesses are worth knowing: it must be kept dry in storage, needs precise cutting since gaps cannot be squashed closed the way wool can, and its foil facings demand taped joints for the designed airtightness. Foil-faced PIR also provides a vapour control layer in many build-ups, which is a benefit when detailed correctly and a condensation trap when not, so build-up guidance from the manufacturer is worth following exactly.

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.