Screed installation methods
Floating Screed vs Bonded Screed
Almost every UFH job today uses a floating screed over insulation. Bonded screed direct to slab still has its place — mainly where insulation already sits elsewhere in the build-up.
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A floating screed sits on a compressible or semi-rigid insulation layer, entirely separated from the structural slab beneath. A bonded screed is mechanically and chemically keyed straight onto a prepared concrete sub-base with no insulation layer between them.
The two solve different problems: floating build-ups are how almost all modern UFH floors are constructed, because the insulation is what stops heat being lost downward into the ground or the floor below. Bonded screeds are used where insulation already exists elsewhere — under the slab itself, for example — and the screed's job is purely to provide the finished floor level.
Choosing between them isn't really optional once you know where your insulation sits; it's largely dictated by the rest of the build-up.
Floating vs bonded screed
| Factor | Floating / Bonded |
|---|---|
| Sits on | Insulation layer / Prepared concrete slab |
| Typical minimum depth | 65–75mm (increases with load) / 25–30mm |
| UFH suitability | Standard modern approach / Only if insulation is elsewhere in build-up |
| Point-load capacity | Lower — needs reinforcement for heavy loads / Higher, direct to structure |
| Common use | New-build and renovation UFH floors / Renovation floors with under-slab insulation |
Practical implications of a floating build-up
- Perimeter isolation strip is essential to allow the floating slab to move independently of walls
- Minimum depth increases with anticipated point loads — heavy furniture or fitted kitchens need checking
- Reinforcement (fibre or mesh) is more commonly specified in floating screeds carrying higher loads
- UFH pipework typically clips directly onto the insulation before the pour
Get your build-up confirmed before you order insulation
Send us your section drawings and we'll confirm whether your project needs a floating or bonded screed before you commit to depths.
Where confusion causes problems
The most common mistake we see on renovation projects is a floating screed specified at bonded-screed depth, because someone assumed the two were interchangeable on thickness. A floating build-up needs more depth to span the insulation and carry point loads without cracking.
If your insulation is already below the existing slab — common in some 1990s and 2000s builds — a bonded screed direct onto that slab may be all that's needed, saving significant floor build-up height.
Floating vs bonded, key numbers
50–65mm over insulation
Floating min. depth
25–40mm on prepared slab
Bonded min. depth
Higher without correct depth/reinforcement
Floating crack risk
Very low when substrate is sound
Bonded crack risk
Floating vs Bonded Screed — questions we get asked
Keep reading across the site
Get your build-up confirmed before you order insulation
Send us your section drawings and we'll confirm whether your project needs a floating or bonded screed before you commit to depths.