How to install insulation ?
Floor Application
Why install underfloor reflective insulation?
Underfloor reflective insulation adds a barrier beneath a floor, helping block cold rising from the ground and radiant heat moving through the floor. It is a good fit under timber floors and raised floors, where there is a void to work in. The photos above show Alumix insulation being installed on floors.
How floor foil insulation works
A reflective foil face turns radiant heat back toward its source, while the foam or multi-layer core adds a thermal break and a moisture-resistant layer. Fitted under the floor with sealed seams and an air gap where possible, it helps keep the room above more comfortable and limits damp air moving upward.
Step-by-step: installing insulation on a floor
- Measure the floor area and plan the rolls so seams overlap by a small margin.
- Clear the void or surface of debris, sharp objects and anything that could damage the foil.
- Cut the insulation to length with a sharp knife or scissors.
- Fix the sheet between or beneath the joists with the reflective face toward the heat source, keeping it taut and leaving an air gap where the layout allows.
- Overlap adjacent sheets and seal all joints with foil tape.
- Seal around pipes, vents and edges so the layer is continuous.
- Check for tears and patch any damage before closing the floor.
Recommended Alumix product
For floors and flat roofs, see Alumix BLH-F 8mm Floor and Flat Roof Reflective Insulation, and browse the wider Alumix product range. Contact the team if you need help choosing.
Tips for floor insulation
- Seal every seam. It keeps ground moisture and cold air from bypassing the foil.
- Keep the underfloor ventilated. Ventilation helps prevent damp in the void.
- Do not compress the foil. An air gap helps it reflect heat.
- Protect from damage. Avoid sharp tools and rough contact once it is fitted.
Frequently asked questions
Can I use foil insulation under a timber floor?
Yes. Reflective foil is commonly fitted under timber and raised floors to reduce cold rising from below.
Does floor insulation need an air gap?
Reflective foil performs best facing open air, so leave a gap where the floor construction allows.
Is it suitable for flat roofs too?
Alumix BLH-F 8mm is designed for floor and flat roof use. Check the product page for details.
Related installation guides
See how to insulate internal walls, attics and lofts, or browse the application gallery.
Relevant Products