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.
Every layer editable · live U-value · Part L & Future Homes Standard targets · free PDF report
The build-up (outside → inside)
- (Ventilated void + ground via ISO 13370)
- Beam & block deck
- 100mm PIR
- 75mm sand/cement screed
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
| Specification | U-value (W/m²K) | Notes |
|---|---|---|
| 150mm PIR + 75 screed, typical semi (P/A ≈ 0.6) | ≈ 0.12 | Current new-build standard |
| 100mm PIR, same floor | ≈ 0.17 | Previous standard spec |
| 75mm PIR, same floor | ≈ 0.21 | Older spec / extensions |
Figures computed to BS EN ISO 13370 with BR 443 conventions, exactly as the pre-filled calculator works them out, with any pass or fail judged on the unrounded U-value. Indicative for the generic build-up and the footprint and depth shown: your products, thicknesses, perimeter, area and ground will move the number, and 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 a junction):
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), the condensation-risk screening check and the thermal-mass figures (decrement factor, time lag, κ) 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, mortar joints in blockwork (and in solid brickwork where BR 443 §4.2 requires them) and air-gap corrections, BS EN ISO 13370 for ground floors, suspended floors and basements, and ISO 13788 for the condensation screening check.
Other common build-ups
Floors
- U-value of an insulated concrete ground floor
- U-value of an insulated suspended timber floor
- U-value of a ground floor with insulation below the slab
- U-value of a floor over a garage
- U-value of an uninsulated concrete ground floor
- U-value of an uninsulated suspended timber floor
- Underfloor heating on a ground floor: insulation and U-value
- U-value of insulation laid over an existing concrete floor
- U-value of a garage conversion floor
- U-value of a basement floor (heated basement)
- U-value of an extension floor (and the whole-house perimeter rule)
- U-value of an insulated raft foundation (EPS raft)
- U-value of a limecrete floor (insulated with foamed glass)
- U-value of a garden room (garden office) floor
- U-value of a solid floor with edge insulation
- U-value of a floor over an unheated cellar
- U-value of an exposed floor over a passage, undercroft or overhang
- U-value of a battened timber floor over a concrete slab
- U-value of a suspended timber floor insulated with wood fibre or sheep’s wool
- U-value of a concrete floor over a car park
- U-value of a warehouse floor slab
Walls
- U-value of a cavity wall with full-fill insulation
- U-value of a cavity wall with PIR partial-fill insulation
- U-value of a timber frame wall
- U-value of a solid brick wall with internal insulation
- U-value of a one-and-a-half-brick (327.5mm) solid wall
- U-value of a solid wall with external insulation
- What is the U-value of an uninsulated cavity wall?
- U-value of a timber frame wall with PIR insulation outside the studs
- U-value of a solid stone wall with internal insulation
- U-value of a cavity wall with external wall insulation
- U-value of a cavity wall with a dense concrete block inner leaf
- U-value of a solid brick wall (9-inch, uninsulated)
- U-value of a solid stone wall (uninsulated)
- U-value of a cavity wall after cavity wall insulation (blown wool or bead)
- Insulated plasterboard on a solid wall: what thickness reaches a U-value of 0.30?
- U-value of a solid wall battened out with insulation
- U-value of a dormer cheek wall (loft conversion)
- U-value of a garage conversion wall (insulating single-skin brick)
- U-value of a SIP wall (structural insulated panels)
- U-value of an ICF wall (insulating concrete formwork)
- U-value of a light steel frame wall (SFS)
- U-value of a timber frame wall with wood-fibre insulation
- U-value of an I-joist timber frame wall (Passivhaus-level)
- U-value of an extension cavity wall (what reaches 0.18)
- U-value of a wide cavity wall (200mm, 250mm, 300mm)
- U-value of wood-fibre internal wall insulation on a solid brick wall
- U-value of external wall insulation with mineral wool
- U-value of a knee wall in a loft conversion
- U-value of a party wall (0.0, 0.2 or 0.5)
- U-value of a basement wall (heated basement)
- U-value of a cellar wall when converting a cellar (basement conversion)
- U-value of a hempcrete wall (hemp-lime)
- U-value of a wall between a house and an integral garage
- U-value of a wall to an unheated corridor or stairwell in flats
- U-value of a CLT (cross-laminated timber) wall
- U-value of a straw bale wall
- U-value of a cob wall
- U-value of aerogel internal wall insulation
- U-value of wood-fibre external wall insulation (EWI) on a solid wall
- U-value of a log cabin wall
- U-value of a garden room (garden office) wall
- U-value of an SFS infill wall with rainscreen cladding
- U-value of a solid aircrete wall (thin-joint blockwork)
- U-value of a shipping container wall
- U-value of a park home wall with external insulation
- U-value of the wall between a house and a conservatory
- U-value of calcium silicate internal wall insulation
- U-value of cork insulation on a solid wall
- U-value of insulating (thermal) plaster on a solid wall
- U-value of brick-slip external wall insulation
- U-value of a tile-hung wall
- U-value of built-up (twin-skin) metal wall cladding
- U-value of an insulated composite panel wall
- U-value of rainscreen cladding on a concrete or blockwork wall
- U-value of a precast concrete sandwich panel
Roofs
- U-value of 270mm loft insulation
- U-value of an uninsulated loft (a ceiling with no insulation)
- U-value of 100mm loft insulation (and what a top-up achieves)
- U-value of 400mm loft insulation
- U-value of insulation between rafters (loft conversion)
- U-value of insulation over the rafters (warm pitched roof)
- U-value of a room-in-roof sloping ceiling
- U-value of a warm flat roof
- Flat roof insulation thickness — about 150mm PIR for 0.15, 140mm for 0.16
- U-value of a cold flat roof (cold deck)
- U-value of an inverted flat roof
- U-value of an uninsulated flat roof (and a warm-deck upgrade)
- U-value of a room-in-roof flat ceiling (collar ceiling)
- U-value of a wood-fibre sarking roof (a vapour-open warm pitched roof)
- U-value of a solid (tiled) conservatory roof
- U-value of a boarded loft (loft boarding over insulation)
- U-value of a green roof (sedum or extensive green roof)
- U-value of a thatched roof
- U-value of spray foam insulation in a pitched roof
- U-value of a cold flat roof converted to a warm roof
- U-value of a garden room (garden office) roof
- U-value of a warm flat roof on a profiled metal deck
- U-value of a roof terrace with paving on pedestals
- U-value of a SIP roof (structural insulated panels)
- U-value of a ceiling insulated from below with insulated plasterboard
- U-value of a garage conversion roof (flat roof insulated from below)
- U-value of a warm flat roof on a concrete deck
- U-value of tapered roof insulation
- U-value of a mansard roof
- U-value of a built-up (twin-skin) metal roof
- U-value of an insulated composite roof panel
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, and why two calculators can give different answers for the same wall.