How to install insulation board between floor joists?

Step: Cut the boards to fit between joists with no gaps. Step: Support the insulation with treated timber battens or metal brackets. Step: Seal any edges with expanding foam or joint tape to prevent air leakage. Step: Install a vapour barrier above before laying your final flooring layer.

How thick should insulation be between floor joists?

For suspended timber floors, 75–100 mm thick insulation is standard. However, it depends on joist depth and target U-value. Thick boards or layered systems can improve efficiency in older or poorly insulated homes.

What is the proper distance between floor joists?

The typical spacing on UK floors is 400 mm or 600 mm in the centre. That means the distance between one joist centre and the next. So it may vary depending on the joist size and load design. To install insulation effectively, confirm joist spacing with your structural drawings or Building Regulations guidance.

Floor Insulation Board

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140mm Celotex XR4140 PIR Insulation Board 2400mm x 1200mm (8′ x 4′) 2.88m2

140mm Celotex XR4140 is a polyisocyanurate (PIR) insulation core with composite aluminium foil facings on both sides. Celotex is a multi-purpose insulation board suitable for use in pitched roofs, ceilings, floors and walls.

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140mm Ecotherm Eco-Versal Rigid PIR Insulation Board 2400mm x 1200mm (8′ x 4′) 2.88m2

The 140mm Ecotherm Eco-Versal is a polyisocyanurate (PIR) insulation core with composite aluminium foil facings on both sides. Ecotherm Eco-Versal is a multi-purpose insulation board suitable for use in pitched roofs, ceilings, floors and walls.

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20mm Kingspan Therma TP10 / TF70 / TW55 PIR Insulation Board 2400mm x 1200mm (8′ x 4′) Pack of 15 (43.20m2)
All three models 20mm Kingspan Therma PIR Insulation Board:
- 20mm Thermapitch TP10
- 20mm Thermafloor TF70
- 20mm Thermawall TW55
share the same high-performance PIR core and low-emissivity foil facings, offering excellent thermal efficiency and easy installation. Although labeled differently, these boards share identical technical specifications.

No longer in production.
£281.72£338.06 Ex VATInc VAT
£6.52£7.82 Per M2 Get restock alert