How to install insulation ?
External Walls
Why use reflective insulation on external walls?
External wall reflective insulation helps stop heat from entering or leaving through the outer walls of a building. Fitted behind cladding or an outer finish, the reflective layer cuts radiant heat gain in warm weather and adds a moisture-resistant layer to the wall. The photos above show Alumix reflective insulation being installed on external walls.
How external wall reflective insulation works
A foil face reflects radiant heat, while the core adds a thermal break between the outside surface and the interior. Together they reduce the heat that passes through the wall. For best results the reflective face should sit next to an air gap, which cladding or battens can create.
Step-by-step: installing reflective insulation on external walls
- Measure the wall area and plan the rolls so seams line up and overlap neatly.
- Check that the wall or frame is clean, dry and free of sharp edges.
- Cut the insulation to length, leaving a small allowance at each end.
- Fix the sheet to the frame with the reflective face toward the outside, keeping it flat and taut.
- Overlap neighbouring sheets and seal every joint with foil tape.
- Seal around windows, doors and penetrations to keep the layer continuous.
- Fit battens and cladding over the insulation to create an air gap and protect the foil.
Recommended Alumix product
For external walls we recommend Multi+ 10mm Fire Rated Multi-Layer IXPE Reflective Insulation. See the product page for details, or contact the Alumix team for guidance on your building.
Installation tips
- Protect the foil. Cover it with cladding promptly so it is not damaged on site.
- Seal openings. Gaps around doors and windows let air bypass the insulation.
- Keep an air gap. Battens in front of the foil help it reflect heat.
- Follow local codes. Check the rules for wall build-ups in your area.
Frequently asked questions
Can reflective insulation be used on external walls?
Yes. It can be fixed to the wall frame behind cladding to reduce radiant heat gain through the wall.
Do external walls need an air gap?
An air gap in front of the reflective face helps the foil perform, so cladding on battens is a good arrangement.
Is it suitable for metal-clad buildings?
Yes. It is widely used in steel-framed buildings. See our guide to metal building insulation.
Related installation guides
Compare with internal wall insulation, or browse the application gallery.
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