Insulating a garage slab

[Adrian80]

Hi guys,

wondering if you can offer a bit of advice.

I am building a new garage, with a raft foundation, however i am wondering if i should add insulation abover the raft and then top it with a screed finish?

Is insulation strong enough to support the weight of a car with a screed top.
I have looked on the jablite and knauf webstites, but it always seems the context is for a habitable room.

Cheers.

A

 

[fmck]

Its not so much the insulation but will the screed be strong enough to spread the load and not flex n crack.

Motorways have been built on top of polystyrene embankments.
We recently enclosed a school courtyard with underfloor heating and screed over insulation and are now running scissor lifts on top. We just as an extra measure put old fence hoarding(plywood) down as an extra precaution.

I would just look at a good concrete screed with decent mesh rebar A393 over the vehicle path area would be more than enough.

 

[Adrian80]

Thanks for the quick reply,

So something like 80mm insulation, 80mm screed with a393 fabric on 40mm risers?

Or would should i go for something a bit thicker?

Cheers
A

 

[fmck]

spacers at the base can go down to 20mm in doors.

Steel in tension, concrete in compression. Steel as close to the base will be most effective but every engineer puts the minimium cover for protection.
DPM goes without saying but if you really want to go to all the bother of insulating a garage :

Make sure the insulation is fully connected around the structure. There is no cold spots through to reduce all the effort and vapour barrier in the floor above insulation.
Got asked about this one from a COW and kingspan does show this in their details. Never seen it done before in a floor but for the price of a bit of polythene worth doing.

 

[fmck]

Sorry, 100mm would be my safe bet but A393 is big enough so your probably right.

 

[^woody^]

Why would you want to insulate a garage floor?

 

[Adrian80]

cheers for the tips, i am doing a load of trench digging tomorrow, so trying to double check all my levels...

Cheers
A

 

[Adrian80]

My thinking it would keep it a bit warmer as a workshop, not sure if it costs more or less than concrete per cubic m.