We get the question often: should we put radiant heat under the new tile or wood floor? Almost always, the answer is yes — with two caveats. First, it has to be specified before the floor is, not after. Second, the build-up has to be drawn and signed off by the people who will lay every layer.
Most of the failures we've inherited (and a few we've caused, early in our practice) come from those two caveats being skipped.
Choose the system before you choose the floor
Two families of system: electric mat and hydronic (water in PEX tubing, fed from a manifold). They behave differently and they have different floor implications.
Electric is the simpler retrofit. Mats lay directly on a clean substrate, then are tiled or wood-floored over with a small thinset cover. Best for single rooms and small bathrooms.
Hydronic is the better whole-house solution. Tubing is set into either a poured screed or a low-profile dry build-up, and a manifold balances loops by room. Slower to commission, more efficient to run, gentler on floors over the long term.
Build-up: the drawing nobody reads, until they have to
For a hydronic system in a Bay Area renovation, a typical build-up over a wood subfloor reads roughly: structural deck, insulation board, PEX tubing in a routed groove or with an aluminium spreader plate, levelling compound (or screed), uncoupling membrane, then tile or wood-finish layer.
Each transition between those layers is a place a job can go wrong. The two we see most: insulation board taped without staggered seams, leaving a thermal bridge; and uncoupling membrane omitted under porcelain, producing tile cracks at the loop boundaries six months later.
What we ask the plumber to do, before tile day
Pressure-test the loops to spec, in front of the studio's lead installer, and leave them under pressure for at least 24 hours before any screed or levelling compound goes down. We have, more than once, found a pinhole leak that would have been a disaster a fortnight after tiling.
Mark every loop centerline on the deck with sharpie before levelling. We need to know where the tubing is when the tile fixings are screwed down at the perimeter.
Document the flow rates per loop at the manifold, on a label that stays in the manifold cabinet. Whoever services the system in five years will thank us.
Commissioning: the slowest part
Radiant systems should not be brought up to temperature suddenly. The first heat cycle is a slow ramp — we use a 14-day commissioning sequence, raising the manifold target by roughly 5°C every two days, with the tile floor allowed to follow.
Skipping this is one of the most common causes of cracked grout and stressed wood floors over radiant. The system works; it's the materials above it that resent the shock.
Wood-floor specifics
Engineered hardwood, three-ply, glued down. Solid hardwood is not compatible — it cups. Floating floors over radiant are technically possible but acoustically unpleasant; we don't specify them.
Wood-finish surface temperature should not exceed 27°C; specify a manifold control that limits flow temperature to keep the floor surface comfortably below that. This is the second most common cause of long-term issues we've seen.
Tile-floor specifics
Use an uncoupling membrane (Schluter Ditra-Heat, or equivalent dry build-up) under porcelain. Keep grout joints tight enough to bridge the loops cleanly. Stick with a flexible, polymer-modified grout — the cheap cementitious grouts will hairline crack over the loop spacing within a season.
Worth it?
For a primary bath, almost always. For a kitchen, often. For a whole house, only if the renovation is already opening up the floor — the value lies in doing it during a tear-up, not retrofitting later.
If you're considering it, tell us early. The build-up affects every layer above it, and we'd rather draw it once than redraw it after the fact.
If radiant is part of your project, talk to us about installation or book a studio session.