Group A · Loft and roof insulation
Flat roof warm deck
PIR insulation over the deck with a new single-ply, GRP, EPDM or felt covering.
Typical price
Flat roof warm deck
£110–£170 per m²
Flat roof warm-deck insulation with new covering
Ask for a quoteBefore grants · updated 11 October 2026 · a survey confirms the final figure.
- Best for
- Extensions, garages, dormers, blocks
- Guarantee or standard
- Covering manufacturer guarantee
- Time on site
- Many domestic flat roofs take a few days, weather permitting.
- Typical price
- £110–£170 per m²
What it is
What is flat roof warm deck?
PIR insulation over the deck with a new single-ply, GRP, EPDM or felt covering.
Best for: Extensions, garages, dormers, blocks.
Build-up
Flat roof warm deck
Outside
Room below
- 1New waterproof coveringSingle-ply, GRP, EPDM or felt
- 2PIR insulation, tapered if needed
- 3Vapour control layer
- 4Existing deck
- 5Joists and ceiling below
Who it suits
Which homes is flat roof warm deck suitable for?
Is my home suitable?
Pick your property type for a straight answer on flat roof warm deck.
Guidance only — every home is different, and a survey confirms what suits yours.
Houses
- Detached house
- Semi-detached house
- End-of-terrace
- Mid-terrace
- Townhouse
- Mews house and cottage
- Detached bungalow
- Semi and terraced bungalow
- Chalet and dormer bungalow
- Period home
- 1930s home
- Post-war and ex-council house
- Non-traditional / system-built
- Listed building or conservation area
- Farmhouse, barn conversion or rural home
- New build or self-build
Flats and blocks of flats
Commercial and public buildings
Usually suitable Depends — a survey confirms
Not usually suitable for 1 property type
- Park and mobile home — Park and mobile homes need specialist systems, which we arrange through a partner rather than standard measures.
Materials and brands
What we use
PIR insulation over the deck with new single-ply, GRP, EPDM or felt covering; tapered insulation schemes to fix ponding.
Insulation brands we work with
- Knauf Insulation (Earthwool, Supafil blown)
- Rockwool
- Superglass
- Isover
- Kingspan
- Celotex
- Recticel
- Xtratherm
- Steico wood-fibre
- YBS and Actis multifoil
The exact system and brand for your home are confirmed in your written quote.
Heat, bills and EPC
What it does for your heat loss, bills and EPC
Heat rises, so a poorly insulated roof is often the largest single route out for heat. Insulating it lowers the roof's U-value — how easily heat passes through — so the heating runs less and the EPC rating usually improves. The gain is largest where there's little insulation now; topping up a loft that's already reasonably insulated gains less.
See the EPC points and savings for your home in the EPC plannerU-value before and after, typical heat and bill saving, and EPC points — worked out for your property.Price
How much does flat roof warm deck cost?
| Service | Typical range, installed |
|---|---|
| Flat roof warm-deck insulation with new covering | £110–£170 per m² |
Indicative ranges for London and the South East, supplied and installed, including VAT. Updated 11 October 2026. A survey confirms your final price.
VAT on this work
Insulation installed in homes in Great Britain is zero-rated for VAT until 31 March 2027. Other parts of a job like this — such as a new roof covering, structural work or waterproofing — may be standard-rated. Your quote shows the split.What to expect
Time on site, disruption and approvals
Time on site
Many domestic flat roofs take a few days, weather permitting.
Disruption
Low — the work happens in the loft or roof space. We need clear access to the hatch, with stored items moved to one side.
Planning and building control
Replacing a flat roof means meeting Building Regulations Part L. The new covering carries its manufacturer's guarantee.
Guarantee and standard
Covering manufacturer guarantee. The guarantee and certification for your job are confirmed in writing in your quote.
60-second grant check
Could a grant help pay for it?
Grant eligibility checker
About 60 seconds · plain results: likely, possibly or not eligible
Before we start
What type of property is it?
Questions
Flat roof warm deck: your questions answered
How much does flat roof warm deck cost?
Typically £110–£170 per m² for flat roof warm-deck insulation with new covering, installed in London and the South East, including VAT and before any grant. Prices updated 11 October 2026. A survey confirms your final figure.
What is a warm deck flat roof?
Insulation laid on top of the roof deck, under a new waterproof covering, so the deck and joists stay warm. It's the standard way to insulate a flat roof because it avoids the condensation risk of insulating between the joists.
Which flat roof covering do you use?
Single-ply membrane, GRP, EPDM rubber or felt — chosen for the roof's use, access and budget. The covering carries its manufacturer's guarantee.
Can you fix a flat roof that holds water?
Yes. Tapered insulation schemes build in a fall, so rainwater drains to the outlets instead of ponding.
Group A
More in loft and roof insulation
Loft insulation
Mineral wool laid between and across the joists to 270–300 mm so heat stays in the rooms below.
Loft insulation top-up
An extra cross-layer over existing insulation to reach the recommended 270 mm or more.
Blown loft insulation
Loose-fill insulation blown into awkward, shallow or low-headroom lofts that rolls can't reach.
Loft clearance and replacement
Old, damp or damaged insulation removed, the loft cleaned, then new mineral wool fitted.
Raised loft boarding and storage
Loft legs or raised boarding over full-depth insulation, so storage doesn't crush it.
Insulated loft hatch and ladders
An insulated, draught-sealed hatch and loft ladder — a small add-on that stops a big leak.
Begin your project
Ready to talk about flat roof warm deck?
Tell us about your home and we'll arrange a survey, then a fixed written quote — no obligation.