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Floor insulation: Insulating suspended timber floors other than ground floor between timber joists

Plasterboard

joists and support attend

Quinn Therm QF PIR Insulation Boards

Pipework & cables

Timber flooring

Internal finish

This floor insulation method is commonly used for upgrading the thermal performance of existing timber floors that are above an unheated space e.g. garage, basement.

  1. Measure the distance between joists and cut insulation boards to fit tight in between

  2. Supports should be added between the timber joists to ensure insulation is supported by either of the following
    • Saddle clips purpose made at 400mm centres
    • Stainless steel nails nailed partially into joists every 400mm centres
    • Timber battens (preservative treated) nailed to the joists

    The supports can be positioned on the joists in order to suit the thickness of insulation so that the insulation remains flush with the top of the joists or lowered to provide a service void below the flooring.

  3. Set the precisely cut Quinn Therm PIR insulation boards between the joists and press down until they sit on the battens, saddle clips or nails. All board joints should be tightly butted ensuring there are no air gaps left between the joists.

  4. A polythene layer can also be installed below the flooring to protect against spillages and reduce air leakage.

How to install insulation in a suspended beam and block floor

1. Supports should be added between the timber joists to ensure insulation is supported by either of the following.

  • Saddle clips purpose made at 400mm centres
  • Stainless steel nails nailed partially into joists every 400mm centres
  • Timber battens (preservative treated) nailed to the joists

2. The supports can be positioned on the joists in order to suit the thickness of insulation so that the insulation remains flush with the top of the joists or lowered to provide a service void below the flooring.

3. A polythene layer can also be installed below the flooring to protect against spillages and reduce air leakage.

Recommended QUINN insulation products

Required insulation thickness of Quinn Therm QF:

Quinn Therm QF between joists U-value (W / m2K)
100 0.25
110 0.24
120 0.22
125 0.21
140 0.20
150 0.19
160 0.18
175 0.16
200 0.15

Based on 25mm un-ventilated air gap next to insulation.

U-value results above based upon floor construction shown:

Plasterboard; timber joists (150mm x 47mm @ 400mm centres); Quinn Therm QF installed between joists; timber flooring (floor finish omitted). Calculations performed to BS EN ISO 6946 and BS EN ISO 13370, taking account of repeating thermal bridges.

Need technical support?

For help and advice on any of our products and how they might fit your needs please contact our Technical by Quinn team.

  • Floor Insulation
  • Pitched Roof Insulation
  • Flat Roof Insulation
  • Wall Insulation