Insulating garage's concrete floor for electric underfloor heating

[alex889]

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

 

[mikeey84]

I would say you want more than 50mm insulation, especially with electric heating, otherwise you may as well burn £5 notes to keep warm

 

[alex889]

I would say you want more than 50mm insulation, especially with electric heating, otherwise you may as well burn £5 notes to keep warm

I've been thinking about 90mm now all around

 

[JohnD]

As you are looking at electric UFH, I presume you either have money to burn, or you do not know anybody who has it?

Which is it?

 

[alex889]

As you are looking at electric UFH, I presume you either have money to burn, or you do not know anybody who has it?

Which is it?

the second option

 

[JohnD]

Ask around.

The normal procedure is to install it, use it until the first bill comes in, then turn it off and never use it again.

 

[mikeey84]

It would work, but you will need to make it so insulated the cost would outweigh installation of alternative heating

 

[alex889]

It would work, but you will need to make it so insulated the cost would outweigh installation of alternative heating

I'm planning to do 90mm all around and floors. Ceiling I may go double 90 layers as I had to add 45x95 joists underneath the existing truss to support it, so I may end up filling it with insulation too.

 

[mikeey84]

I would not think that is enough tbh, but give it a go!

 

[Mottie]

As long as it’s reasonably well insulated, a couple of 2 kw heaters would be more than enough for that size surely?

 

[alex889]

I would not think that is enough tbh, but give it a go!

What would you recommend?

 

[alex889]

As long as it’s reasonably well insulated, a couple of 2 kw heaters would be more than enough for that size surely?

I did some calculations, with well insulated space, for 5m2 it seems I would need bare minimum 400W heater, as I'm planning to divide the space into 2 offices, the final area will be 4.8m2