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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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A suspended timber floor - featuring timber joists spanning supporting walls - is extremely unlikely to be used for a new ground floor construction. Where an existing building does feature a suspended timber ground floor, the void below is ventilated to help prevent decay of the floor joists. However, that airflow draws warm air from the heated space above through the floorboards, making those rooms harder to heat and keep warm.

What Celotex products are suitable for suspended timber ground floors?

To improve the thermal performance of the floor, insulation can be fitted between the joists. Older buildings typically feature smaller joist depths, limiting the space available for insulation. It makes sense, therefore, to use high performance insulation.
 
Celotex GA4000 and Celotex XR4000 are both lightweight, rigid polyisocyanurate (PIR) foam insulation boards. With their low thermal conductivity, they are well suited to minimising the insulation thickness in suspended timber ground floor applications. They offer the following benefits:

  • Quick and easy to install insulation between joists in one layer.
  • Boards retained by Celotex Insulation Clip.
  • Minimise air leakage by friction fitting the insulation.
  • Reliable long-term energy savings for buildings.
  • Low emissivity foil facers improve thermal performance within air spaces.
  • Minimal load added to the structure due to lightweight boards.

Installing Celotex insulation in suspended timber floors

If a suspended timber ground floor features in a new-build project, it is likely to be over a basement. The basement will be part of the building’s thermal envelope - in other words, it is a heated space - and the floor will not require thermal insulation.
 
In an existing building, the timber joist ends are likely to be built into external walls that may have no, or an ineffective, damp proof course. 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.
 
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

XR4000
1200 x 2400mm
110-200mm
0.022 W/mK

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GA4000
1200 x 2400mm
50-100mm
0.022 W/mK

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