Screed and Underfloor Heating
Underfloor heating is not judged the day it warms up: it is judged the day the screed cracks — and by then it is already under two centimetres of tile.
Overview
TAV. 00Underfloor heating warms by low-temperature radiation: water at 30–35 °C instead of 70, even comfort and no visible radiators. But it moves all the difficulty onto the screed, which becomes a technical element: it must bury the pipes with no voids, expand freely when heated, and cure completely before being covered. Every shortcut in those three things is paid for with a crack — and a crack in a heated screed is not cosmetic: it is a pipe working in shear.
The site score
TAV. HThe detail of the craftroom to expand
The base and the perimeter strip
Cleaning the slab, checking levels and fitting the compressible strip along every wall, column and threshold.
You trim the strip after the flooring, never before: cut it now and you've thrown away its whole job.site notebook — editorial synthesis
click a beat · arrow keys ← → walk the site · dashed pauses are the chemistry at work
Why it cracks
The screed with nowhere to go
A heated screed grows a few millimetres per metre. With a perimeter strip and joints it moves and comes back; wedged between walls, the only way it can make room is to break.
This is why the strip is trimmed only after the floor is laid, and screed joints must be carried through the finish: if the flooring bridges them, the crack travels through the tiles.
The time you cannot compress
Thirty days before the floor
This is the phase where the site looks idle and is in fact working: the screed cures, then the commissioning cycle makes it perform all its thermal movements, and only afterwards does the instrument say whether it is ready.
The times given are orders of magnitude: the governing value is always the measured residual moisture, which depends on thickness, binder type and season.
How it ages (and what betrays it)
TAV. PQuestions from the site
TAV. QCan I put parquet over underfloor heating?
Yes, but with constraints: stable species and limited thickness, fully bonded laying, and the commissioning cycle is mandatory. Wood insulates more than tile, so output drops: that must be allowed for in the design, not discovered afterwards.
How thick is the build-up in a refurbishment?
Traditional systems need 8–12 cm; low-profile systems of 2–4 cm exist, using high-performance insulation. They cost more and have less inertia — heating up faster but cooling faster too — so they need more responsive controls.
Can the commissioning cycle be skipped in summer?
No: it is not there to heat the house but to make the screed complete its thermal movements before a floor is glued on top. It is run even in August, and it must be recorded — that record protects everyone if something cracks later.
Can the same system cool in summer?
Yes, by circulating cool water, but with a physical limit: if the surface falls below dew point, condensation forms on the floor. That requires humidity control and dehumidification, otherwise you risk a wet, slippery floor.