Thickness Of Insulation Under Concrete Floor

Insulation is laid on the concrete and covered with a screed.

Thickness of insulation under concrete floor.

A 50mm thick layer of proprietary floor slab insulation is usually enough to reach and maintain the target u value but this should be checked with an architect first. Place the insulation edge to edge using duct or other construction tape to hold the insulation together. 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. Depending on the use of the building the slab can then be finished ready for use or receive a screed suitable for a floor finish.

Designers generally insulate both directly under the slab and around the perimeter as well. The first important thing to pay intention to is the depth of the floor slab. Step 4 place 2 inch thick pieces of rigid styrofoam insulation on top of the plastic sheeting. In cold climates it is advisable to use a minimum of 2 inches of extruded polystyrene under the slab.

The plastic serves as a vapor barrier preventing moisture from passing up through the gravel to the concrete floor above. 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. There will be a damp proof membrane under the insulation and possibly a second membrane on top depending on the type of screed. 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.

Many builders will baulk at this figure it was not long ago that installing 50mm of insulation in the floor was considered fairly advanced. If the insulation is going below the slab the damp proof membrane dpm is laid next followed by the insulation a polythene separating layer and the concrete slab.