Celotex Isover

Insulation for Beam and Block Floors

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Compared to the wet trades involved when insulating above or below a concrete slab, suspended concrete floors offer a fast, effective, dry operation. The floor can be a beam and block (also called block and beam, or pot and beam) deck or, on larger projects, a precast concrete plank craned into position.

Suitable for use on projects where a concrete slab might ordinarily be used, suspended concrete decks are particularly desirable where there is unstable ground, a high water table, or too much poor soil needs removing. They also make it easier to provide a level floor on sites with an excessive slope.

A concrete deck is not at risk of rot like the joists in a suspended timber ground floor, but the sub-floor void must still be ventilated to prevent any potential build-up of gas.

In a block and beam deck, concrete blocks are laid between, and supported by, concrete beams shaped like an inverted ‘T’. The lighter the block, the greater its contribution to the thermal performance of the floor; it’s also possible to use infill blocks made from expanded polystyrene insulation.

Installing thermal insulation below a concrete deck is not usually an option, so rigid insulation is installed above the deck. Lightweight, rigid polyisocyanurate (PIR) foam insulation boards (such as Celotex GA4000 and XR4000), are among the most thermally efficient, commonly available insulation materials. They keep the depth of the floor construction down, and are easily handled and laid to quickly insulate large areas.

With an appropriate separation layer installed over, such as light-gauge polythene, they are then easily covered by a concrete screed or tongue and groove chipboard, ready to receive the specified floor finish.

Thinner polyisocyanurate (PIR) foam insulation boards, such as Celotex TB4000 can be considered for the perimeter upstand insulation.

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