Celotex Isover

Insulation for Suspended Timber Floors

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All ground floor constructions, unless very large commercial floors, will require some insulation to be included within the floor zone to comply with Building Regulation requirements. If the ground floor in question is of a suspended timber construction, and whether this is a renovation or new-build project, then the insulation would normally be installed in the joist zone – that is installed between the joists.

A rigid polyisocyanurate (PIR) board can be installed between the joists (Celotex GA4000 and XR4000 can be considered) provided the insulation is cut accurately and fitted carefully to avoid air gaps. Thinner polyisocyanurate (PIR) foam insulation boards, such as Celotex TB4000, can be considered for the perimeter upstand insulation.

Another choice for insulating between the joists would be a glass mineral wool (GMW) roll or slab – the flexible nature of this type of product means it can be cut slightly oversize and then compression-fitted between the joists to eliminate air gaps. Some support may be needed for the insulation - timber straps, timber battens or netting can all be utilised to help keep the insulation in place.

The floor would typically be finished from above with a vapour control layer (VCL) if required and a suitable timber floor deck.

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
ISOVER Spacesaver 100-200mm Spacesaver: Width 1160mm, Length 5200-12180mm | Spacesaver Ready-Cut: Width 3x386 or 2x580mm, Length 5200-12180mm | Spacesaver Lite: Width 1160mm, Length: 3500-7000mm 0.044 W/m.K
ISOVER Spacesaver Plus 100-200mm Width 1160mm, Length 3500–7000mm 0.040 W/m.K