Portsmouth at a glance
- Postcode districts
- PO1, PO2, PO3, PO4, PO5, PO6
- Population
- about 208,100 (GeoNames)
- Council area
- Portsmouth City Council
- Building approval
- Portsmouth City Council building control, or a registered building control approver
- Nearest main town
- Southampton, about 15 miles
- Guide price region
- South East (+10% on West Midlands rates)
Why upgrade to a warm roof in Portsmouth?
Converting a garage, loft space or outbuilding to a room in Portsmouth changes what the roof needs to do. Once the space is heated, the roof is expected to perform to a higher standard, and a warm build-up is usually the simplest way to get there.
In and around Portsmouth, flat roofs are typically found on low-rise post-war blocks of flats, and on 1930s semis with flat-roofed garages and kitchen extensions. Much of the South East sits in the drier Thames catchment at roughly 730 mm of rain a year, so the usual failures are at joints, upstands and outlets rather than from sheer volume of rain.
How much does a warm roof upgrade cost in Portsmouth?
For Portsmouth we use South East rates: £3,100–£5,350 is the guide for a 20 m² extension roof in EPDM with a new deck and insulation, VAT included. 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 | £3,100–£5,350 |
| Extension (20 m²), EPDM with sedum green roof | £4,850–£8,900 |
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?
- Survey of the deck, joists and existing insulation
- New waterproofing, with a written workmanship guarantee
- Upstands, trims and kerbs reset to the new roof level
- 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 Portsmouth: questions
Do you cover Portsmouth?
Yes. Portsmouth is part of our Hampshire coverage, including postcode districts PO1, PO2, PO3, PO4, PO5, PO6. 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 Portsmouth?
Where the work needs approval it goes to Portsmouth City Council 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 Portsmouth?
£3,100–£5,350 for a 20 m² extension roof in EPDM with a new deck and insulation, at South East 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.
Is a warm roof worth it on a garage?
On a detached, unheated garage, usually not, as there is no heated space to protect and the thermal rules don't normally apply. On an integral or heated garage, or one being converted into a room, it is.