Depth Insulation Under Concrete Floor

The first important thing to pay intention to is the depth of the floor slab.

Depth insulation under concrete floor.

Many builders will baulk at this figure it was not long ago that installing 50mm of insulation in the floor was considered fairly advanced. Many increase the under slab insulating foam board thickness to 3 or 4 inches at the outer 2 to 4 feet of the slab. In this scenario a rigid foam insulation is usual and as you d want the same u value in the roof we need the same thickness of insulation 180mm. The target u value for a concrete ground floor slab is 0 22 and these days the insulation must be provided around the edge of the floor slab as well.

Where the heating is likely to be turned on and off such as in new build domestic properties and a faster thermal response is required the floating floor arrangement of insulation above the slab can be more appropriate. On the other hand if you are laying insulation on top of the existing slab than you will need to make sure that there are no construction. Insulation below the slab suits continuous low level heating gradually warming the thermal mass of the concrete and sustaining it at a consistent temperature. In climate zones 4 and 5 the code requires certain slabs below grade slabs that are less than 12 in.

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 is laid on the concrete and covered with a screed. Foamular does not absorb water like other types of foam board which makes it ideal for below grade and under slab installations. If the slab has hydronic tubing the minimum r value of this insulation increases to r 15.

The math is pretty simple the thicker the concrete floor insulation material the deeper the slab will have to be. Home depot does sell the right solution for residential concrete slab insulation. Below grade to have r 10 vertical insulation at the slab perimeter extending downward from the top of the slab to a depth of at least 2 ft. If this is the situation you find yourself in the dpm will sit above the concrete and your moisture resistant chipboard will go on top beneath the flooring surface.

There will be a damp proof membrane under the insulation and possibly a second membrane on top depending on the type of screed. This allows an area for insulation and fill material under the slab. In cold climates it is advisable to use a minimum of 2 inches of extruded polystyrene under the slab. Excavate the area under the slab to 12 inches below the planned level of the top of the slab.

Foamular provides r 5 per inch of thickness winter and summer. Phenolic foam is a popular choice to get around this issue as it s able to achieve strong levels of insulation for less depth. This stops any thermal bridging across the walls leading to cold spots.