Install Under the Batten

How to install insulation ?

What is under-batten roof insulation?

Under-batten roof insulation is a layer of reflective foil fitted beneath the roof battens, so it forms a tight thermal layer directly under the roof covering. It is a popular choice for tile and metal roofs, and it works well when the roof covering is already in place. The photos above show how Alumix foil insulation is installed under the batten.

Why install foil insulation under the batten?

• Reflects radiant heat. The foil face turns away heat from a sun-heated roof before it reaches the space below.
• Suits existing roofs. You can fit it from below without removing the roof covering.
• Helps control condensation. A sealed layer limits warm, moist air reaching cold roof surfaces.
• Affordable and lightweight. Foil rolls are easy to carry, cut and fix.

Step-by-step: installing foil insulation under roof battens

1. Measure the roof underside and work out how many rolls you need, allowing a small overlap at each seam.
2. Check the underside for sharp nails, screws or burrs and remove or flatten them.
3. Unroll the insulation against the underside of the rafters with the reflective face toward the roof covering.
4. Keep the sheet taut and fix it along the rafters so it does not sag.
5. Overlap adjacent rolls and seal each joint with foil tape.
6. Fix the battens over the insulation, which also holds it firmly in place.
7. Inspect the finished layer and patch any tears.

Recommended Alumix products

• Bronze FR 4mm Fire Rated Reflective Foil Insulation
• Alumix Silver 6mm Basic/FR Insulation
• Multi+ 10mm Fire Rated Multi-Layer IXPE Reflective Insulation
• RADWRAP T180 REF Breathable Reflective House Wrap

Check each product page for details, or ask the Alumix team which roll fits your roof.

Tips for a tight, lasting installation

• Seal every seam so the layer works as one continuous barrier.
• Avoid compressing the foil against other surfaces, since an air gap helps it reflect heat.
• Handle rolls carefully and patch small tears straight away.
• Keep the roof space ventilated to help moisture escape.

Frequently asked questions

Can I fit insulation under battens on a tile roof?

Yes. Under-batten foil insulation is commonly used beneath tiled roofs as well as metal roofs.

Is under-batten insulation better than over-purlin insulation?

Neither is better in every case. Over the purlins is simplest on a new build before the roof covering goes on, while under the batten suits a roof that is already finished.

Do I need to leave a gap?

Where the layout allows, leave an air gap in front of the reflective face, because foil insulation performs best facing open air.

Related installation guides

See how to fit insulation over the purlins, how to treat an attic or loft, or browse the application gallery.