Underfloor heating floor systems explained: screed, overlay, joisted and electric

The right system depends on three things: the floor you have now (solid concrete, timber joists or an existing finished floor), how much height you can lose, and your heat source. A heat pump wants a system that works at low water temperatures. A small bathroom retrofit wants the thinnest build-up.

This guide compares the four systems with build-up heights, how each one is laid and where each one fits best.

What are the types of underfloor heating floor system?

The four types are screed (also called solid floor), overlay (low profile), joisted (timber floor) and electric. The first three use water pipe fed from a manifold. Electric uses a heating cable or mat wired to a thermostat.

Heights for overlay and electric are the product figures for MaxHeatUFH boards and mats. Screed depths are typical figures from screed makers and trade guidance.

How does a screed underfloor heating system work?

In a screed system the water pipe is fixed over insulation and then buried in screed, which stores heat and spreads it evenly across the floor. It gives the highest output at low water temperatures, which is why it is the first choice with a heat pump.

There are three ways to hold the pipe before the pour:

• Clip or staple. Barbed clips are fired through the pipe into the insulation board with a tacker gun.
• Clip rail. Self-adhesive rails hold the pipe at set centres.
• Castellated panel. The pipe pushes in between raised bosses, with no clips. Our 1220 x 820mm panel takes 15, 16 or 17mm pipe.

Screed depth depends on the type:

• Sand and cement. Trade guidance gives 75mm as the minimum for a floating screed on insulation, with 65mm normally accepted in domestic housing.
• Liquid calcium sulphate. One maker specifies a minimum of 25mm (30mm nominal) cover over the pipe. Another system maker suggests 35mm cover, about 50mm in total over 15mm pipe.

Fit edge insulation round the room before you pour, so the screed can expand and heat does not leak into the walls. Our guide to screed depths and drying times covers this in more detail.

How long does screed take to dry before I can use the heating?

As a rule of thumb, screed dries at about 1mm a day. One liquid screed maker quotes 1mm a day up to 40mm, then 0.5mm a day beyond that, in ideal conditions. So a 50mm liquid screed takes about 40 + 20 = 60 days to dry fully, and a 65mm sand and cement screed takes at least 65 days.

The heating can sometimes be used to help drying, but only as the screed maker allows. One calcium sulphate screed maker allows force drying from 7 days. One system maker says not to switch on until at least 21 days after laying a sand and cement screed. Always follow the data sheet for the screed you use, then commission with a slow warm-up.

What is an overlay or low-profile system?

An overlay system uses thin grooved or castellated boards laid over an existing floor, so you avoid digging up the slab. Most add 15 to 25mm and you can tile directly on top, so there is no screed to wait for.

Overlay floors have less mass than screed, so they warm up and cool down faster. They suit well-insulated rooms. In a high heat loss room, check the output before you choose an overlay. Read low-profile overlay boards for laying and tiling tips.

How do you fit underfloor heating in a joisted timber floor?

For timber floors you either lay 22mm routed chipboard on the joists, or fit aluminium spreader plates between or under the joists. Both keep the pipe within the floor depth and use the aluminium or a foil layer to spread heat.

1. Routed chipboard. Screw 22mm P5 grooved chipboard to the joists, press the pipe into the grooves, then lay a 6mm foil-backed top board. MaxHeatChip has grooves at 150mm centres and covers 0.72m² per 1200 x 600mm board.
2. Spreader plates from above. Fit insulation between the joists, lay aluminium plates over the joists, clip in the pipe and fix the new deck on top.
3. Fit from below. Where you can reach the joists from a cellar or open ceiling, fix double spreader plates from underneath and leave the floorboards down.

Timber systems usually need a warmer flow temperature than screed. The MCS Heat Emitter Guide's examples show an aluminium panel floor with tiles needing 45°C at 150mm centres for a 4 star rating, where screed with tiles reaches 6 stars at 35°C and 100mm centres. See underfloor heating in joisted timber floors for a full comparison.

How does electric underfloor heating differ?

Electric underfloor heating uses a heating cable instead of water pipe, so there is no manifold, pump or pipework. It is cheaper to install but more expensive to run, according to the Energy Saving Trust, so it suits single rooms more than whole houses.

• Mats. Cable fixed to a self-adhesive 0.5m wide mesh. Our mats are about 3 to 4mm thin and sit in the tile adhesive bed. They come in 100, 150 and 200W/m².
• Loose cable. Pressed between the studs of an uncoupling membrane at the spacing you need. It suits L-shaped or awkward rooms where a mat will not fit.

Use a floor-sensing thermostat and a 30mA RCD, and have the final connection made by a qualified electrician to BS 7671. Compare the two in electric loose cable vs mats.

Which floor system should I choose?

Choose by your floor and heat source. Use this as a quick decision list:

1. New slab or extension, any heat source: screed. It gives the most output at the lowest flow temperature.
2. Existing solid floor, little height to spare: overlay boards, tiled direct.
3. Upstairs or timber ground floor, floor coming up: routed chipboard or spreader plates from above.
4. Timber floor you cannot lift but can reach from below: fit-from-below spreader plates.
5. One bathroom or kitchen with a tiled finish: electric mat or loose cable.

Many homes mix systems: screed in a new extension, overlay in the old kitchen and chipboard upstairs, all from the same heat source. Each floor type has its own output, so design each room for its own build-up. With a heat pump, read underfloor heating with a heat pump before you decide.

What does each system cost in boards?

Board or panel cost per m² varies by system. These are MaxHeatUFH board prices only (inc VAT, October 2026), not including pipe, manifold or controls.

• MaxHeatPanel 25mm for 16mm pipe: £12 per 0.72m² board, about £16.70 per m².
• MaxHeatDeck 20mm: £15 per 0.72m² board, about £20.80 per m².
• MaxHeatFix Plus, pack of 10: £79 per 7.2m², about £11 per m².
• Castellated floor panel 1220 x 820mm: £9 per sheet (1m²).
• MaxHeatChip 22mm for 16mm pipe, 2400 x 600mm: £68 per 1.44m² board, about £47.20 per m², plus the 6mm top board at £16 per 0.72m².
• Electric mat 150W/m², 10m²: £224.

Add a few extra boards for cuts. ProLoop works out the exact board count, pipe and manifold for your rooms.

Products for this job

• Castellated panels for screed and levelling compound
• Overlay boards
• MaxHeatDeck Cement-Faced Routed XPS Board
• Joisted floor systems
• MaxHeatChip Grooved Chipboard Panel (22mm)
• Edge Insulation Foam Roll
• Electric underfloor heating mats

Frequently asked questions

What is the best underfloor heating system for a new build?

A water screed system is usually the best choice for a new build. It gives the highest output at low flow temperatures and pairs well with a heat pump. Plan the insulation and screed depth into the floor build-up early.

Can underfloor heating go on an existing concrete floor?

Yes. Overlay boards such as MaxHeatPanel or MaxHeatFix go straight over a sound, level concrete floor and add about 15 to 25mm. You can tile directly onto them.

How thick is a liquid screed over underfloor heating?

Liquid calcium sulphate screed is usually around 40 to 50mm in total, with makers specifying between 25mm and 35mm of cover over the pipe. Check the data sheet for the screed you use.

Can you put underfloor heating upstairs?

Yes. Use routed chipboard, spreader plates or an overlay board on the existing deck. Electric mats also work under tiles upstairs.

Do I need insulation under underfloor heating?

Yes. Insulation under the pipe sends heat up into the room rather than down into the slab or void. Our routed XPS and EPS boards have insulation built in. Read insulation under underfloor heating for more.

Is electric or water underfloor heating better?

Water is cheaper to run and suits whole houses. Electric is cheaper and quicker to install and suits single rooms. See water vs electric underfloor heating.

Which underfloor heating system responds fastest?

Electric mats and overlay boards respond fastest because there is little mass to heat. Screed is the slowest to warm up but holds heat the longest.

Sources: MPA Mortar Data Sheet 22 (screeds), Gyvlon flowing screed data pack, Timoleon staple system data sheet, MCS 021 Heat Emitter Guide, Energy Saving Trust