Attic Insulation

How to install insulation ?

Why insulate your attic or loft with reflective foil?

Attic and loft foil insulation tackles the heat that builds up under a roof. In summer the roof space can become extremely hot and pass that heat into the rooms below, and in winter it is a major route for heat loss. Reflective foil, often called a radiant barrier, reflects radiant heat and works well on loft floors and under roof slopes. The photos above show Alumix insulation being installed in an attic.

Two ways to insulate an attic or loft

On the roof slope

Fitting foil to the underside of the rafters keeps the roof space inside the insulated envelope and reflects heat from the roof covering. This is useful when the loft is used for storage or living space.

On the loft floor or ceiling

Laying or fixing foil at ceiling level separates the living area from the roof space. It suits lofts that are not used and is often the easiest option for a DIY project.

Step-by-step: installing foil insulation in an attic

1. Measure the area and decide whether you are insulating the roof slope or the ceiling.
2. Clear the space and remove or flatten any sharp nails and screws.
3. Cut the insulation to length, leaving a small allowance for overlaps.
4. Fix the sheet to the rafters or joists with the reflective face toward the heat source, keeping it taut.
5. Overlap neighbouring sheets and seal every joint with foil tape.
6. Keep vents, flues, cables and recessed lights clear, following the required clearances.
7. Check the finished layer for gaps and tears before closing up the space.

Recommended Alumix products

• Save Cool Mega 40mm Multi-Foil Ceiling and Loft Insulation
• Save Cool Triplex 25mm Thermal Break Reflective Insulation
• Multi+ 10mm Fire Rated Multi-Layer IXPE Reflective Insulation
• Extra FR Net 16mm Multi-Foil Reflective Insulation

See each product page for details, or contact the Alumix team to pick the right roll.

Tips for loft insulation

• Do not block ventilation. Keep eaves and roof vents open so moisture can escape.
• Tape every seam. A continuous layer limits heat and moisture movement.
• Leave an air gap. Foil works best when the reflective face looks into open air.
• Take care of electrics. Keep cables and fittings clear of the foil as required.

Frequently asked questions

Does foil insulation work in an attic?

Yes. Reflective foil is well suited to attics because so much of the heat in a roof space is radiant.

Should I insulate the roof slope or the loft floor?

Insulate the roof slope if you use the loft as living or storage space, and the loft floor if the roof space is empty.

Can I install it myself?

Many homeowners do. See our DIY applications page for simple guides and products.

Related installation guides

Compare with installing under the batten, insulation on beams, or the full application gallery.