Insulation build-up compared
PIR vs EPS Insulation Under a Liquid Screed
Both sit under the pour and carry the UFH thermal load — but they don't perform the same, and swapping one for the other changes your finished floor level.
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Before a single litre of screed goes down, the insulation layer underneath it has already decided a lot about how the floor will perform — how much heat gets pushed upward through UFH, how much floor build-up height you lose, and how it behaves under point loads from furniture and foot traffic.
PIR (polyisocyanurate) and EPS (expanded polystyrene) are the two insulants we're asked to price against most often. They look similar on a drawing but behave quite differently underfoot and underheat, and neither one is a straight drop-in replacement for the other at the same thickness.
This page sets out the technical differences we actually account for on site, so you can have an informed conversation with your architect or building control before the insulation order goes in.
PIR vs EPS — the numbers that matter
| Property | PIR vs EPS |
|---|---|
| Thermal conductivity | ~0.022 W/mK vs ~0.035–0.038 W/mK |
| Thickness for same U-value | Thinner PIR layer vs thicker EPS layer |
| Compressive strength | Typically 120–150kPa vs 70–120kPa (grade-dependent) |
| Cost per m² | Higher material cost vs lower material cost |
| Moisture behaviour | Foil-faced, low absorption vs closed-cell, low absorption |
| Cutting on site | Clean straight cuts vs can shed beads if cut roughly |
Where PIR earns its higher price
- Renovations with a fixed finished floor level and no room to build up thickness
- Loft conversions or extensions where every millimetre of head height counts
- Passive-house or high-performance-spec builds chasing a very low U-value
- Commercial floors needing high compressive strength under racking or plant
Get your insulation and screed build-up priced together
Send us your floor plan and finished floor level constraints and we'll come back with a PIR or EPS recommendation plus a screed quote.
PIR vs EPS — quick decision guide
Choose PIR when…
- Floor height is tightly constrained
- You need the lowest U-value achievable
- Budget allows the premium
- Heavy point loads are expected
Choose EPS when…
- Depth isn't a constraint
- Cost per m² is the driver
- Standard residential UFH loads
- Large open-plan areas with generous build-up
PIR wins when floor height is the constraint — it buys you the same U-value in less thickness. EPS wins when depth is available and budget matters more than millimetres. Test it against your finished floor level drawing, not the insulation datasheet alone.
— Exeter Liquid Screeders
PIR vs EPS Insulation — questions we get asked
Keep reading across the site
Get your insulation and screed build-up priced together
Send us your floor plan and finished floor level constraints and we'll come back with a PIR or EPS recommendation plus a screed quote.