Sarking Board Buyer’s Guide: Membranes, Boards and Roof Insulation Options
Sarking is the layer fixed over rafters (or sometimes over a boarded roof) before the tiling battens and roof covering. On traditional roofs that might be bituminous felt; on many modern warm or hybrid roofs it may be a breathable membrane, and some specifications call for rigid sarking boards. This guide explains what buyers usually mean, and what Insulation Warehouse Direct actually stocks.
Quick answer
We do not currently list a dedicated branded “sarking board” product line. For roof build-ups we do sell roof insulation / PIR, breather membranes (including DuPont Tyvek), OSB and other sheet materials, plus SuperFOIL multifoil where a thin reflective layer is specified. Always follow the roof designer’s detail — the wrong board or membrane in the wrong place can trap moisture.
What people mean by sarking
- Felt or membrane sarking: a flexible underlay over rafters.
- Boarded sarking: timber or wood-based sheets fixed over rafters, sometimes as a structural or fire-related deck, with a membrane over.
- Insulated warm-roof build-ups: PIR above or between rafters with the correct vapour control and breathable layers — see warm roof PIR build-up and related warm/cold roof guides on our blog as they go live.
Materials we can supply for roofing / insulation crossovers
| Need | What we stock | Link |
|---|---|---|
| Breathable roof underlay / housewrap | DuPont Tyvek and related tapes | breather membranes / DuPont Tyvek |
| Rigid insulation for pitched or flat roofs | Celotex, Kingspan, Recticel PIR; Thermaroof TR24 for flat roofs | roof insulation / PIR |
| Wood-based sheathing | OSB3 sheets | OSB |
| Thin multifoil options | SuperFOIL SF19+ and related | SuperFOIL |
| Vapour control | VCL membranes and vapour boards | vapour control layers |
Buying advice
- Get the roof build-up drawing first (cold roof, warm roof, or hybrid).
- Confirm whether you need a membrane, a board, insulation, or all three.
- Check U-value targets with our PIR U-value calculator and Part L guidance in what U-value you need.
- If a named sarking board brand is on the spec and we do not list it, ask us — we will say honestly if we cannot supply it and suggest the closest stocked alternative only where it is appropriate.
Frequently asked questions
Do you sell Celotex or Kingspan as sarking?
PIR boards are insulation, not a direct substitute for every sarking board detail. Use them only where the roof design calls for that insulation layer.
Can I use OSB as sarking?
Some traditional boarded roofs use wood-based sheets; whether OSB is acceptable depends on the structural and fire design. Ask your designer — we supply the sheets, not the sign-off.
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 deliver roof membranes to Scotland?
Breather membranes and most ranges are England delivery; Celotex and Knauf loft roll have wider coverage — see the table.
| 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 | – |
Company: Bay Drywall and Insulation Supplies Ltd (company no. 14473556), Unit 3 Babbage Court, Totnes Industrial Estate, Totnes, Devon TQ9 5JE.