The layer that decides whether the heating you paid for ends up in the room or in the ground. Membrane, board and edge detail laid tight and laid right, then screeded over by the same team on the same visit.
Board type and thickness worked back from the U-value your build has to hit, not picked off what is on the wagon. PIR, EPS and XPS all have a place and they are not interchangeable.
DPM lapped, taped and dressed up the perimeter before a board goes down. Insulation over a torn membrane is an expensive way of doing nothing.
Boards cut in tight and the joints staggered so there is no straight path through the layer. Gaps between boards are cold bridges and they show up as cold strips in a finished floor.
Edge strip up every wall and every upstand so the screed is not bridged to a cold wall and has somewhere to move to when it heats up.
Compressive strength matched to what the floor is carrying. A domestic room and a floor taking racking need very different boards under the same looking screed.
Resilient and acoustic layers built in where a floor has a separating performance to meet, detailed so the screed above it stays isolated from the structure.
Usually rigid board. PIR gives the best performance per millimetre so it suits floors where height is tight, EPS is cheaper and often the sensible choice where you have the depth, and XPS gets used where the board has to take real load or sit somewhere wet. What is right for your floor comes off the U-value target and the loading, and we will tell you which one and why.
On a new build floor you are typically looking at 100 to 150mm of rigid board to hit current Building Regulations, but it depends entirely on the board, the perimeter to area ratio of the room and what else is in the build up. It is worth getting the number from the actual floor rather than a rule of thumb, because being 25mm short is not something you can fix later.
Yes, and it does two jobs. It stops the screed touching a cold external wall, which would otherwise pull heat straight out at the edges of the room, and it gives the screed room to expand when the heating comes on. Floors that crack around the perimeter are very often floors where this strip was left out.
It needs it more than anything else in the build. A heated floor is trying to push warmth upward, and without a good insulation layer under it a large share of that heat goes down into the ground instead. Skimping on the insulation to save on the build up is the single most common reason an underfloor heating system disappoints.
Sometimes. If there is height available you can lay a thin high performance board and a low profile screed over the existing floor, which loses some ceiling height and needs the door and threshold heights checking first. If there is no height to give up, the honest answer is that the floor has to come out, and we would rather say that at the quote than halfway through.
Based in Bolton, working across the North West as a matter of course and taking planned work anywhere in the country.