Namely if you are only digging the slab you will need to take into account the thickness of the insulation since it will affect the depth of the slab.
Insulation under garage floor slab.
Pinning the apron to the slab is just doweling some 4 rebar into the garage slab at each door writes dave richeson.
Floor 1 garage 3 under slab 5 more ways to filter.
Insulate your garage to reduce energy bills and protect your garage against harsh outdoor temperatures.
But when adding insulation to an existing slab the vapor barrier is laid over the top of the slab before the foam insulating panels are installed.
These f factors are acceptable for all slab on grade floors but you need to make sure.
Connecting slab and aprons tying rebar in the slab to sidewalls may not be necessary or even advisable but at least one post suggests that connecting the main floor slab to the aprons at door entrances is a good idea.
Average pir insulation will easily support normal garage loads under a 150mm slab.
Concrete is cold and hard but an insulated concrete slab can make a heated garage significantly warmer and more energy efficient.
Is it worth it to insulate under a concrete slab.
Otherwise both codes require that slab on grade floors with a floor surface less than 12 in.
The codes are silent about whether above grade slabs need to be insulated.
There is no insulation under the slab.
These codes do not require any insulation for slabs that are more than 12 in.
How to insulate a garage floor above a concrete slab.
The first important thing to pay intention to is the depth of the floor slab.
Through nearly all of the winter the temperature a few inches above the floor stays in the upper 30s f.
The back ten feet of the garage structure is an unheated workshop area separated from where the cars park by a framed wall 2x4 and door.
Below grade need vertical insulation at the slab perimeter.
Really you can forget the imposed vehicle load and just work out the concentrated load which should be minimum 9kn for vehicles up to 2500kg.
The math is pretty simple the thicker the concrete floor insulation material the deeper the slab will have.
Dealing with the edges the foam insulation and two layers of plywood can add as much as 2 inches of height to the garage floor.
I am presuming there is a 4ft deep footing around the perimeter of the garage with no insulation.
Consult appendix a table a6 3 1 in the 2016 edition for a tabulation of assembly f factors for slab on grade floors based on the arrangement and rated r value of the applied insulation.
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