Celotex Isover

Insulation for Upgrading Concrete Slab Floors

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Converting existing unheated basements, garages and storage areas into habitable rooms is a popular way of increasing living space without constructing an extension. Such spaces typically have a sound, level concrete slab floor - but lack sufficient floor insulation to achieve the thermal performance targets for new habitable rooms.

If headroom is tight then the only option may be to break up the existing slab, dig further down and build up an entirely new floor. Where it’s possible to avoid that, however, upgrading the floor slab is a viable solution, adding a damp proof membrane (DPM) if not already present before installing the insulation.

Headroom is unlikely to be limitless though! So it makes sense to keep the make-up of the floor upgrade as thin as possible, which means using a high performance insulation product. Lightweight, rigid polyisocyanurate (PIR) foam insulation boards, such as those manufactured by Celotex, are among the most thermally efficient, commonly available insulation materials.

They are easily handled, meaning floors are quickly insulated ready to receive a light-gauge polythene separating layer and - depending on the height available - either a concrete screed or a thinner tongue and groove chipboard.

Key Considerations

When using Celotex or ISOVER products, you need to satisfy yourself that use of the product meets all relevant national Building Regulations and guidance as well as local, national and other applicable standards relevant for your construction or application, including requirements in relation to fire and applicable height restrictions. In addition to the product datasheet, please refer to the following product documents:

The building detail is for illustrative purposes only. It does not constitute advice and should not be relied upon.


Insulation products
Product Name Thickness Range Sizes Lambda
Celotex XR4000 110-200mm Width 1200mm, Length 2400mm 0.022 W/m.K
Celotex GA4000 50-100mm Width 1200mm, Length 2400mm 0.022 W/m.K
Celotex TB4000 20-40mm Width 1200mm, Length 2400mm 0.022 W/m.K