Is wet or electric underfloor heating better for an extension?

Wet UFH connected to the boiler is the right choice for a single-storey extension with significant glazing and open-plan living, because it heats the slab evenly and avoids cold spots near bifold doors. Electric mat systems cannot keep a 20m2-plus open-plan space warm in a UK winter and should not be the primary heating.

Should you use liquid screed or sand-and-cement over underfloor heating?

Liquid anhydrite screed is the better choice over UFH: it self-levels, flows around the pipes without air pockets, and conducts heat more efficiently than hand-laid sand-and-cement. Builders often quote the sand-and-cement price for a liquid screed job, so the real number can come as a surprise.

Why is underfloor heating screed more expensive than the builder quoted?

Builders routinely price for sand-and-cement, which is what they know, but liquid screed is the right product over UFH and costs more per square metre. The gap between the £800 – £1,500 a builder quotes and the £2,000 – £3,000 liquid screed actually costs on a 50m2 floor is the most common cost surprise of the whole first-fix phase.

Why must underfloor heating be pressure-tested before screed is poured?

The system is pressurised and held while the screed flows over it, which proves there are no leaks and keeps the pipes from floating or shifting in the wet screed. Once the screed sets, a leaking pipe means breaking up the entire floor to find it, so this is your one chance to confirm the system is sound.

What flooring can you lay over underfloor heating?

Tiles, whether porcelain, ceramic, or stone, are the best option because they conduct heat well and tolerate thermal cycling. Luxury vinyl tile and suitable engineered wood also work, but solid wood is risky and carpet acts as a blanket that blocks the heat.

Back to Single Storey Rear Extension

Phase 6 · First Fix · Task 05 of 06

Underfloor Heating in Your Extension

Wet UFH planning, installation, and screed for single-storey extensions: pipe spacing, the liquid-versus-sand-and-cement screed decision, floor build-up, and the screed cost surprise most homeowners never see coming.

17 min readUpdated 2026Premium

Timeline infographic showing the UFH critical path from insulation through pipe laying, pressure testing, screed pour, curing, and tiling readiness

Prerequisites

Complete these first

Your builder will quote you £800 – £1,500 for screed. The actual liquid screed bill will be £2,000 – £3,000. That gap is the single most common cost surprise in the entire first-fix phase, and it catches almost every homeowner who hasn't been warned.

Wet underfloor heating is the right choice for a single-storey extension. It's more efficient than radiators, invisible once installed, and gives you even heat across an open-plan space with no cold spots near bifold doors. But the installation itself is a coordination exercise involving your plumber, your builder, and a specialist screed company, all working to a tight sequence where one delay cascades into weeks of lost time.

Here's the full process: what goes into the floor, who does what, when screed gets poured, and the specific hold points where you need to check the work before it disappears under 50mm of liquid concrete.

What this guide covers

01Wet vs Electric: One Decision, No Contest
02What Goes Into the Floor
03The Screed Decision
04Timing: The Three-Day Window
05The Pressure Test: Your One Chance
06Floor Level: The Problem Nobody Mentions Until It's Too Late
07After the Pour: Curing, Commissioning, and Laitance
08Floor Coverings: What Works and What Doesn't
09Screed Edges and Expansion Joints
10What It Costs
11Building Regulations and Controls
12Commissioning Documentation
13Key External Resources

Premium content — unlock with an Access Pass

This guide is part of the Kitchen Extension Access Pass. Get full access to every section — from planning through to completion.

Get Access Pass

One-time payment. 24 months access.