Lewisham at a glance
- Postcode districts
- SE6, SE13, SE4, SE23, SE26, SE12, SE10, SE20
- Council area
- London Borough of Lewisham
- Building approval
- London Borough of Lewisham building control, or a registered building control approver
- Guide price region
- London (+20% on West Midlands rates)
Why upgrade to a warm roof in Lewisham?
In a place like Lewisham, homeowners usually think about insulation when the roof covering is worn out. That is the right moment, because the thermal rules normally apply to a replacement over a heated room, and adding insulation then costs far less than doing it separately later.
In a town like Lewisham, flat roofs are commonly found on kitchen extensions and roof terraces behind period houses or Victorian and Edwardian terraces with flat-roofed back additions. The Thames basin is one of the drier parts of Britain at roughly 730 mm of rain a year, but summer heat is the bigger test here: dark membranes on south-facing roofs swing a long way in temperature.
How much does a warm roof upgrade cost in Lewisham?
Guide price in Lewisham: £3,350–£5,850 for a 20 m² extension roof in EPDM with a new deck and insulation, including VAT at London rates. The fixed price comes after a free survey for new and replacement roofs.
| Job | Guide price inc VAT |
|---|---|
| Extension (20 m²), EPDM, new deck + insulation | £3,350–£5,850 |
| Extension (20 m²), EPDM with sedum green roof | £5,300–£9,700 |
Can a cold flat roof be converted to a warm roof?
Yes, and it is the usual approach when an older cold roof is re-covered. The old covering is stripped, the deck is checked and replaced where needed, and the vapour control layer, insulation and new waterproofing go on top.
The existing insulation between the joists is assessed at the same time. Leaving it in place can create a cold, unventilated gap that traps moisture, so it is often removed or the build-up is designed so that most of the insulation sits above the deck. We decide this case by case once we can see inside the roof. If the covering is still sound and you are only patching it, the upgrade isn't usually required, and our repair or replace guide explains how to decide between the two.
What's included?
- New waterproofing, with a written workmanship guarantee
- Building control or building standards handled where needed
- Survey of the deck, joists and existing insulation
- Rigid insulation boards sized to the U-value target
Building regulations in England
Replacing more than half of a flat roof over a heated room usually counts as renovating a thermal element, so the roof is insulated to around 0.16 W/m²K where that's technically and economically feasible, and the work is notified to building control: the council or a registered building control approver, unless a registered competent person self-certifies it. A roof on a new extension is built to 0.15 W/m²K. Patch repairs, and most unheated detached garages, don't trigger the upgrade. Structural changes, or a new covering that adds 15% or more to the roof's weight, also need approval. More on the rules.
Which nearby areas do we also cover?
Warm roof insulation upgrades in Lewisham: questions
Do you cover Lewisham?
Yes. Lewisham is part of our London coverage, including postcode districts SE6, SE13, SE4, SE23, SE26, SE12 and 2 more. Surveys and roofs are carried out by vetted roofing teams working under S&K Property Investments and Improvement Ltd.
Who checks building regulations for a flat roof in Lewisham?
Where the work needs approval it goes to London Borough of Lewisham building control, or a registered building control approver. We tell you at the survey whether your job needs it and deal with the paperwork as part of the quote.
How much does a warm roof upgrade cost in Lewisham?
£3,350–£5,850 for a 20 m² extension roof in EPDM with a new deck and insulation, at London guide rates including VAT. The fixed price comes after a free survey for new and replacement roofs.
How thick does flat roof insulation need to be?
It depends on the insulation product and the U-value target. With common PIR boards, meeting a renovation target usually means well over 100 mm. Thinner, higher-performance boards are available where height is tight.
Will a warm roof make my room warmer?
Usually, yes. A room under a poorly insulated flat roof loses less heat once the roof is upgraded and tends to feel more even in temperature. How much difference you notice depends on how the roof was built before.