Ground Floor Insulation

Insulation for Beam and Block Floors

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 in the floor 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  SOPRATHERM GA4000 and XR4000 (previously known 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 SOPRATHERM TB4000 (previously known as Celotex TB4000) can be considered for the perimeter upstand insulation.

In a solid or ground-bearing (because it is continuously supported by the ground across its whole area) concrete floor, the choice of insulation position relative to the concrete slab is commonly linked to the building’s heating system.

Insulation below the slab suits continuous, low level heating, gradually warming the thermal mass of the concrete and sustaining it at a consistent temperature. 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. The sub-floor is prepared using well-compacted hardcore and a layer of sand blinding.

• 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. 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.
• Where insulation is positioned above the slab, the slab and DPM can be installed either way round. The insulation is then laid, followed by a polythene separating layer, and either a concrete screed or tongue and groove chipboard, ready to receive the specified floor finish.

Lightweight, rigid polyisocyanurate (PIR) foam insulation boards such as SOPRATHERM GA4000 and XR4000 (Previously Celotex GA4000 and XR4000), are among the more thermally efficient insulation materials commonly available. They help keep the overall depth of the floor construction down, meaning less excavation, and are easily handled and laid to insulate large areas efficiently. Thinner polyisocyanurate (PIR) foam insulation boards, such as SOPRATHERM TB4000 (previously Celotex TB4000), can be considered for the perimeter upstand insulation.

For low-rise buildings on poor ground, the floor slab can be designed as a raft to act as the foundation. While SOPREMA PIR boards have good compressive strength, they are not designed to be installed below a raft slab to take the structural load of a building. They can, however, be installed above the raft slab in the same arrangement as described above. For non-domestic buildings, you should seek advice from a structural engineer regarding the suitability of any insulation product within a specific floor system.

In a solid or ground-bearing concrete floor (where it is continuously supported by the ground across its whole area), the position of the insulation relative to the concrete slab is typically influenced by the building’s heating system.

Insulation for Suspended Timber Floors

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 SOPRATHERM GA4000 and XR4000 (previously 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 SOPRATHERM TB4000 (previously Celotex TB4000), can be considered for the perimeter upstand insulation.

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

Insulation for Upgrading Concrete Slab Floors

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 SOPRATHERM(Celotex) GA4000 and XR4000) 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.

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

When using SOPREMA 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:

• BBA certificates - where applicable to the application
• Declarations of Performance
• Health & safety datasheets
• Calculating the P/A ratio leaflet