DIY Doctor UK DIY Forums

Hello!

I have a 12m2 garage with a concrete floor that I would like to insulate and use electrical underfloor heating as it will become a home office. I'm doing it all myself but I’m not sure what is the best procedure and/or order of putting it all together.

My first idea was first to repair cracks and holes with mortar, then self level it as the concrete surface is full of tiny waves/grooves, lay a damp proof membrane, lay the 50mm PIR boards on top, then electric underfloor heating mats stick to the PIR boards, self-level again and then a laminated or vinyl floor.

The concerns and questions I have or were raised by talking to some people

* I may not need to self level the concrete slab to take these waves/grooves imperfections, the PIR boards once layed on top of them and walked on top should absorb these. True?
* 50mm PIR boards for a 12m2 garage could be overkill?
* PIR board should not be in direct contact with electric underfloor heating, I guess it can be burnt/melted by the wires? It seems I would need to add a separation layer, some suggested some concrete faced insulation boards so the heat from electrical wires would spread more evenly on the surface and not damage the PIR boards underneath
* Should I chipboard on top of the PIR boards (which has the wires and self level already in place) as they are weak and could get damaged easily with point pressure even with the self-level on top?
* Is chipboard the best option to add a hard layer between the PIR boards and the laminated floor?
* I was checking screed, but the requirement seems to be 50mm of screed on top of underfloor heating wires and that with already 50mm PIR board means a fair bit of headroom gone, plus the curing time for screed of several weeks. I was checking liquid screed with faster drying times, but I'm not sure it is worth the costs

This is a DIY project, and I was told that I should just get some regular electric radiators in place, but I want to learn and try as I may one day build my own house so the garage is my guinea pig as I can invest more in materials when I'm doing all the work :)

The advice you have is correct, don't put electric underfloor heating directly on PIR board, it will just melt straight through. Search for "Insulated Tile Backer Board" or "Underfloor Heating Insulation Board", unfortunately it's a lot more expensive but the right material for the job. It may be overkill to use this board on top of PIR board, especially if you're restricted to a certain finish level. If you're constructing on top of the existing floor, I would go... Repair/level existing floor, then Damp Proof Membrane, then Insulated Backer Board, then Underfloor Heating Matts. You might not need a finishing screed as some laminates are suitable to place directly onto the heating matts - but not all, so best to do some more research.

fuseboxwales wrote:The advice you have is correct, don't put electric underfloor heating directly on PIR board, it will just melt straight through. Search for "Insulated Tile Backer Board" or "Underfloor Heating Insulation Board", unfortunately it's a lot more expensive but the right material for the job. It may be overkill to use this board on top of PIR board, especially if you're restricted to a certain finish level. If you're constructing on top of the existing floor, I would go... Repair/level existing floor, then Damp Proof Membrane, then Insulated Backer Board, then Underfloor Heating Matts. You might not need a finishing screed as some laminates are suitable to place directly onto the heating matts - but not all, so best to do some more research.

I'm sort of giving up on underfloor heating as the cost to prepare the floor and the running costs compared to an electric radiator are not very favourable. I'm thinking now about just put a DPM in place, insulation boards, chipboard and then vinyl flooring on top and rely on electric radiators for heating