How to Insulate a Balcony or Terrace: Materials Buyer’s Guide
Insulating a balcony or roof terrace is a waterproofing and structural job first, and an insulation job second. This guide covers the insulation materials Insulation Warehouse Direct sells that appear in terrace and balcony build-ups — mainly thin high-performance boards and multifoil — and is honest about what we do not do.
Quick answer
Balcony and terrace upgrades usually need a designed warm-deck or inverted build-up with a compatible waterproofing system. We supply flat-roof PIR, Kingspan phenolic / PIR where specified, and SuperFOIL multifoil for some lightweight or retrofit details. We do not supply the full waterproofing membrane systems or install terraces. Get a roofing contractor or designer’s detail before ordering boards.
Why balconies and terraces are different
- They are outside weather lines — insulation must sit in a build-up that stays dry and drained.
- Upstand heights, thresholds and door cills often limit thickness.
- Inverted roofs (insulation above the waterproofing) need boards rated for that use — check the datasheet; do not assume a general-purpose PIR is suitable.
- Structural load and falls to drains matter as much as U-value.
Materials paths we can help with
| Approach | Materials we stock | Caution |
|---|---|---|
| Warm deck with PIR below the waterproofing | Thermaroof-type flat roof PIR and general roof boards — roof insulation | Board facing must suit the waterproofing system |
| Limited depth / secondary lining under a terrace soffit | PIR or multifoil on the underside where the detail allows | Still needs condensation risk thinking |
| High performance in thin depth | Kingspan Kooltherm phenolic boards where the spec allows — check product pages | Kingspan range |
Related reading: warm roof PIR build-up, SuperFOIL for lofts, terraces and extensions.
What to order once you have a detail
- Board type and thickness from the drawing.
- Compatible tape and VCL if the warm-deck detail needs them (membranes, membrane tapes).
- Delivery date confirmed when we process the order — call 03330 908479 for deadlines.
Frequently asked questions
Do you sell balcony waterproofing kits?
No — we focus on insulation and drylining materials.
Can I put ordinary Celotex on top of a terrace membrane?
Only if the waterproofing manufacturer and board datasheet allow that inverted use. Many general PIR boards are not for inverted roofs.
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 stock vacuum insulated panels for terraces?
No — see our VIP explainer for thinner alternatives we do sell.
| 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.