Extension roof replacement
An extension roof needs a sound deck, suitable insulation, positive drainage and a weatherproof junction with the house. Single-storey extensions are usually flat or low-pitch, with EPDM, GRP or liquid waterproofing above a warm-deck build-up. We assess the whole roof, not just the covering, and coordinate the roofing work with your builder where needed.
Choosing the covering for an extension roof
The shape and details help decide the system. EPDM rubber suits straightforward roof areas, while GRP fibreglass gives a rigid finish that can suit more involved shapes. Liquid systems are another option where junctions and penetrations need a detailed approach. Each needs a compatible substrate and properly finished edges.
Rooflights, outlets, changes in level and the wall connection should be planned before the covering is ordered. A new membrane cannot solve a poorly positioned outlet or an upstand that is too low. Our flat roofing guide explains the broader system choices if you are still comparing materials.
Warm decks, insulation and falls
A warm deck places insulation above the structural deck. Modern Building Regulations effectively require this approach for new extensions because the roof must demonstrate suitable thermal performance. The build-up needs U-value compliance, moisture control and properly connected insulation at the wall junction, rather than simply adding a thin board under the waterproofing.
Insulated PIR boards can be laid to falls so water runs towards the outlets. The insulation thickness, vapour control layer and finished heights need agreeing together. Door thresholds, rooflights and existing windows can limit available height. These details should be resolved before construction reaches the roof, not improvised after the deck is in place.
The junction with the existing house
The roof-to-wall connection is a separate part of the job. Lead or a suitable proprietary flashing is detailed into the existing brickwork, with the waterproofing turned up beneath it. Sound masonry and a properly finished chase matter: a good covering can still leak if water gets behind the wall flashing.
On replacement work the old covering comes off so the deck can be checked for damp or decay. We also look at falls and outlets before deciding what can remain. Repeated staining inside the extension may come from a failed junction rather than the centre of the roof, so the survey follows the water path rather than assuming the whole surface is at fault.
Working with your builder and Building Control
We can work alongside your builder or main contractor, with the programme agreed in advance. The roof specification, structural readiness and access need lining up before installation. Agree who is responsible for rooflight openings, deck preparation and surrounding masonry so important details do not fall between separate trades.
New extension roofs need Building Control sign-off. We supply the roofing paperwork, including the relevant build-up and as-built information, to support that process. Sign-off is for Building Control to confirm; it is not something a roofer can replace with a verbal assurance. On an existing extension, we explain the proposed replacement scope and any compliance requirements that need checking.
Cost of an extension roof
Every extension roof is quoted after a survey that includes a deck check, because the covering system, insulation build-up, required deck repairs and access all affect the price. The written quote sets out the full scope for your roof rather than a generic allowance.
GRP and liquid options are quoted after a survey. For the cost of a new extension roof, provide the drawings and proposed insulation details if available; for replacement, photographs and approximate dimensions help plan the visit. Compare our flat roof replacement costs, then request a free written quote with the scope set out.
Related roofing advice
Extension roof replacement FAQs
Do I need warm deck or cold deck?+
Modern Building Regulations effectively require warm deck on new extensions. Insulation above the deck supports U-value compliance and condensation control. Any alternative needs a specific design rather than a like-for-like assumption.
How much does an extension roof cost?+
We quote after a survey that includes a deck check. The covering system, the actual build-up, insulation and access all affect the price, so the written quote sets out the scope for your roof rather than a generic figure.
Can you work alongside my builder?+
Yes. We agree the programme in advance with your builder or main contractor, including when the deck will be ready and who is responsible for the adjoining details.
Does the roof need Building Control sign-off?+
Yes, on new extensions. We supply the roofing paperwork to support the approval process, including the relevant build-up information. Building Control confirms sign-off.
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Contact Stoker Property Solutions for new roofs, flat roofing, repairs and maintenance across Newcastle, Sunderland and the wider North East.