How To Insulate a Suspended Timber Floor (2 methods)

This step by step guide explains how to insulate suspended timber floors using our Multifoil Insulation materials, such as EcoQuilt Expert, EcoQuilt45 and SuperQuilt.

There are two simple ways to install multifoil insulation beneath a timber floor. If the floorboards are being removed, the insulation can be recessed part way into the floor joists from above. Alternatively, if you have access beneath the floor through a cellar or crawl space, the insulation can be installed as a continuous taut layer underneath the joists.

Remove the Existing Floorboards

Carefully remove the existing floorboards to expose the timber floor joists.

Before installing the insulation, check that the joists are dry and in good condition and make sure any existing ventilation beneath the suspended floor remains clear.

Measure and Cut the Multifoil

Measure the length of the floor area and roll the EcoQuilt Expert or SuperQuilt across the joists.

Run the insulation perpendicular to the direction of the joists and cut it to the required length using multifoil insulation scissors or a cutting knife.

Allow enough material to recess the insulation between each joist.

Recess the Multifoil Between the Joists

Push the multifoil part way down between each floor joist to create an air cavity between the insulation and the floorboards above.

A piece of timber can be used as a simple depth guide to keep the insulation at a consistent level across the floor.

Staple the multifoil to the sides of each joist using a Heavy Duty Staple Gun and 14mm staples. Keep the material secure and evenly tensioned as you work across the floor.

Install the Next Section

Repeat the process with the next length of multifoil.

Overlap adjoining sections by approximately 50mm to maintain continuous insulation coverage across the floor.

The overlapping joints should be left untaped in this application to help any moisture dissipate and allow the timber floor structure to breathe.

Seal Around the Perimeter

Once the insulation has been installed, use ThermaSeal Foil Joining Tape to seal around the perimeter of the floor.

Pay particular attention to the edges of the room where draughts could otherwise pass around the insulation and into the room above.

Reinstall the Floorboards

Once the multifoil is securely fitted, reinstall the floorboards directly onto the timber joists.

The recessed insulation creates an air cavity above and below the multifoil, helping the reflective layers work effectively while taking up very little additional floor height.

Method 2: Installing Multifoil Under Floor Joists From a Crawl Space

Before starting, make sure you have safe access to the underside of the floor.

Check that the timber joists are dry and in good condition and ensure all existing air bricks and underfloor ventilation openings remain completely unobstructed.

Staple the Multifoil Under the Joists

Starting at one side of the floor, position the multifoil across the underside of the timber joists.

Staple the insulation directly to each joist using a Heavy Duty Staple Gun and 14mm staples.

Pull the material taut as you work across the floor and staple into each timber joist at approximately 300mm intervals.

Install the Next Section

Position the next length of multifoil alongside the first, maintaining a minimum 50mm overlap between each section.

Continue measuring, cutting and stapling until the entire underside of the floor has been covered.

Keep each section taut and make sure there are no large gaps in the insulation coverage.

Finish Around the Perimeter

Trim the multifoil neatly around the edges of the floor and any structural timbers, pipes or other obstacles.

Seal around the perimeter where appropriate using ThermaSeal Foil Joining Tape to help minimise draughts passing around the edges of the insulation.

Do not block air bricks or other ventilation openings within the crawl space.

Disclaimer – Ecohome-Insulation cannot be held responsible for any losses financially or physically from advice provided in this How-To-Guide.

SuperQuilt and EcoQuilt should always be installed as per the manufacturer's recommendations and data sheets.

We always recommend using good building practice when installing our products.