U-value of a beam and block floor with PIR

The new-build suspended concrete floor: beam & block, PIR, screed.

The current new-build standard — 150mm PIR under a 75mm screed — gives a U-value of about 0.12 W/m²K calculated to BS EN ISO 13370 §9.2 on a typical dwelling footprint, which clears the 0.13 notional. The older 100mm build-up shown below comes out nearer 0.17 on the same floor: still inside the 0.18 limiting value, but no longer notional-standard. It is the default suspended floor of volume housebuilding.

Open this build-up in U-Monkey — pre-filled, free

Every layer editable · live U-value · Part L & Future Homes Standard targets · free PDF report

The build-up (outside → inside)

The pre-filled link opens with U-Monkey’s default footprint (P/A 0.6) — edit to your floor.

Typical U-values for this construction

SpecificationU-value (W/m²K)Notes
150mm PIR + 75 screed, typical semi (P/A ≈ 0.6)≈ 0.12Current new-build standard
100mm PIR, same floor≈ 0.17Previous standard spec
75mm PIR, same floor≈ 0.21Older spec / extensions

Figures computed with the BS EN ISO 6946 combined method (bridging included) using BR 443 conventional lambda values — indicative for the generic build-up shown. Your products, thicknesses and (for floors) footprint will move the number: that's what the calculator is for.

What changes the number

As with all ground floors, perimeter-to-area does the quiet work — check the same spec on your actual footprint. Edge insulation and the wall-floor junction detail (a ΨMonkey job) decide how much of the paper performance you keep.

Next: check the junctions

A U-value covers the flat area of an element — but heat also escapes where elements meet, and at modern U-values those junctions can be 20–30% of a dwelling's fabric heat loss. Now you know your U-values, model the junctions with the free ΨMonkey psi value calculator (no subscription; PDF reports £25 +VAT):

Or read thermal bridging explained to see how junction Ψ-values feed your SAP calculation.

Frequently asked questions

What is the U-value of a beam and block floor with PIR?

The current new-build standard — 150mm PIR under a 75mm screed — gives a U-value of about 0.12 W/m²K calculated to BS EN ISO 13370 §9.2 on a typical dwelling footprint, which clears the 0.13 notional. The older 100mm build-up shown below comes out nearer 0.17 on the same floor: still inside the 0.18 limiting value, but no longer notional-standard. It is the default suspended floor of volume housebuilding.

Does the insulation go above or below a beam and block deck?

Above, almost always — rigid boards over the deck, screed or chipboard over the boards. It keeps the insulation continuous and the calculation clean. Model it in U-Monkey with your real perimeter and area for the ISO 13370 figure.

Is this calculator free?

Yes — building the element, reading the U-value, the compliance targets (including the Future Homes Standard) and the condensation-risk screening check are all free in your browser, and the Building Control-ready PDF report is free too. No sign-up.

Does it follow the official calculation method?

Yes — the combined method of BS EN ISO 6946:2017 with BR 443 conventions, including timber bridging and air-gap corrections, ISO 13370 for ground and suspended floors, and ISO 13788 for the condensation screening check.

Other common build-ups

Different build-up? See the full floor U-value calculator, or start from scratch in the main U-value calculator.

Need the wider compliance picture? U-values feed straight into SAP calculations — or let our New Build Compliance Pack handle the lot. Background reading: what U-values actually are.

Your build-up won't be exactly this one.

It never is. Open this one pre-filled, then swap the insulation, change the thicknesses and watch the U-value move — free, in your browser, with a Building Control-ready PDF at the end.