When to Use Foil Tape with PIR Insulation Boards
Foil-faced PIR boards are often detailed with aluminium foil tape over the joints. This short buyer’s guide covers when that tape is needed and which tape Insulation Warehouse Direct sells.
Quick answer
Use foil tape on PIR joints when the manufacturer’s installation guidance or your designer’s detail calls for a continuous foil facing — typically to support airtightness and the reflective facing’s role in the U-value calculation. We stock Alpha Foil Tape 50mm, 75mm and 100mm rolls. Tape is not a substitute for a separate vapour control layer where one is specified.
When to tape
- Board joints lightly butted, clean and dry before taping.
- Follow the board maker’s jointing notes (Celotex/Sopratherm, Kingspan, Recticel each publish fixing guides).
- Around service penetrations, tape alone may not be enough — use the detail specified (collars, sealant, proprietary closers).
When tape is not enough on its own
Warm roofs, timber frames and some wall linings need a dedicated vapour control layer with lapped and sealed joints. Foil tape on PIR helps the board facing; it does not automatically replace a VCL sheet. See moisture control and compare with breather membranes on the cold side of the build-up (breather membranes).
Which width?
50mm suits many board joints; wider tapes (75–100mm) help on uneven joints or where the detail asks for greater lap. Check your drawing. Browse membrane tapes for related sealing tapes.
Frequently asked questions
Can I use duct tape instead?
Use foil tape rated for insulation joints — ordinary cloth duct tape is not what manufacturers specify for foil facings.
Do I tape both faces?
Usually the facing that the detail treats as continuous — follow the board installation sheet.
Do you install insulation, do surveys or help with grants?
No. Insulation Warehouse Direct sells insulation materials online. We do not install insulation, carry out surveys or handle grant applications. If you want it fitted, use a qualified installer, and for grants check the official GOV.UK energy schemes. We are happy to supply the materials your installer specifies.
Do you sell expanding foam for gaps?
Check current accessories on site; large gaps should be cut-and-fitted with board, not filled with foam as a substitute for insulation thickness.
| Where | What we deliver | Delivery charge |
|---|---|---|
| England | All ranges | Free on insulation, plasterboard and drylining from £400 ex VAT. Celotex: £400 ex VAT minimum, free delivery. Access panels: £15 + VAT under £300 ex VAT, free from £300 |
| Mainland Wales and mainland Scotland | British Gypsum (including Gypframe), Celotex, Knauf and access panels | £400 ex VAT minimum plus £40 + VAT (access panels: £15 + VAT under £300 ex VAT, free from £300) |
| Scottish islands | Not delivered | – |
| Northern Ireland | Not delivered | – |
Order PIR boards with foil tape in the same delivery where possible. Company: Bay Drywall and Insulation Supplies Ltd (company no. 14473556), Unit 3 Babbage Court, Totnes Industrial Estate, Totnes, Devon TQ9 5JE.