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Insulation for Suspended Timber Floors

Specifying Celotex PIR insulation is quick and easy to cut and ensures no thermal bridging occurs at floor gaps making it the ideal flooring insulation solution for suspended timber floors

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Although common in older domestic properties, it’s rare for new ground floors to be constructed using timber joists spanning between supporting walls. Where they are constructed to separate ground floor spaces from below-ground rooms, a modern basement typically forms part of the thermal envelope so thermal insulation of the floor between is not a concern.

Sub-floor voids are ventilated to help prevent decay of the floor joists. However, that air flow draws warm air from the heated spaces above through the floorboards, making those rooms harder to heat and keep warm.

To improve the thermal performance of the floor, insulation can be fitted between the joists. Depending on the age of the property and the timber sizes used, the available depth can be limited and it makes sense to use a high performance insulation.

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 and cut to fit between the joists, and the low emissivity foil facings can improve the thermal resistance of airspaces they face into.

As with any retrofit proposal, you should seek expert help in assessing the potential consequences of new measures on other parts of the building fabric. This is particularly true of suspended ground floors, where the timber joist ends are likely to be built into external walls that may have no, or an ineffective, damp proof course.

Ventilation and the movement of moisture, especially around the joist ends, can be affected by the installation of new insulation measures, and protecting the structural floor is critical. A more involved, but potentially better long-term, retrofit option is to remove the timber joists and build up a concrete floor from the sub-floor ground level, with insulation above or below the concrete slab.


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Celotex products to consider

1200 x 2400mm
0.022 W/mK

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1200 x 2400mm
0.022 W/mK

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