Service
Flat Roof Insulation Upgrades
Any flat roof being replaced now has to meet Part L insulation values. We upgrade extensions and outbuildings to warm-deck spec — and your heating bill will notice.
- Warm deck PIR / Celotex spec
- Part L compliant U-values
- Vapour control layer below
- EPDM, GRP or torch-on finish
- Tapered insulation for falls
- No internal disruption
Warm deck vs cold deck — and why warm wins
Cold deck flat roofs (insulation between joists) are hard to make compliant and prone to interstitial condensation. Warm deck (insulation above the deck, membrane on top) is the modern standard — drier, warmer, longer-lasting.
What Part L actually requires in 2026
Replacement flat roofs must achieve a U-value of 0.18 W/m²K — typically 120–150mm of PIR depending on board type. We design the build-up and provide the calculation as part of the quote.
FAQs
Does insulation add much to the price?+
PIR boards add £25–£45 per m² to the build-up cost. On a 20m² extension that's £500–£900 — usually paid back in heating savings within a few winters.
Can you add tapered insulation for falls?+
Yes — cut-to-fall PIR is the cleanest way to build falls into an existing deck without disturbing the joists.
Need Roofing Work You Can Rely On?
Speak with Butler Bespoke Roofing for honest advice, a free site visit and a clear, written quote anywhere across Buckinghamshire.