Northampton at a glance
- Postcode districts
- NN1, NN2, NN3, NN4, NN7
- Population
- about 245,899 (GeoNames)
- Council area
- West Northamptonshire Council
- Building approval
- West Northamptonshire Council building control, or a registered building control approver
- Nearest main town
- Milton Keynes, about 15 miles
- Guide price region
- East Midlands (−2% on West Midlands rates)
What makes a good extension roof in Northampton?
Condensation drives some replacements in Northampton. Older extension roofs were often built cold, with insulation between the joists and no reliable vapour control. Warm air from the kitchen reaches the cold deck, moisture builds up and the timber suffers. A warm roof deals with the cause, not just the stain.
Around Northampton, flat roofs are common on 1930s semis with flat-roofed garages and kitchen extensions and on shops with flat-roofed rear stores below flats. The East Midlands is drier than the west of Britain, so most flat roofs here fail through age, UV and poor detailing at upstands rather than sheer rainfall.
How much does a new extension roof cost in Northampton?
At East Midlands guide rates, a 20 m² extension roof in EPDM with a new deck and insulation comes to £2,750–£4,800 including VAT. 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 | £2,750–£4,800 |
| Extension (20 m²), GRP, new deck + insulation | £2,950–£5,300 |
| Extension (20 m²), EPDM, insulation + 1 rooflight upstand | £2,950–£5,150 |
| Single garage (18 m²), EPDM rubber | £1,550–£2,750 |
Why does water pond or leak where the extension meets the house?
Usually because the fall runs the wrong way, the abutment detail has failed, or the roof has sagged close to the wall. The junction with the house is the most common leak point on an extension roof.
If the roof falls towards the house, or the deck dips near the wall, water sits against the upstand and finds any weakness in the flashing above. Older roofs often have the felt simply turned up the brickwork with no cover flashing, or a flashing that has pulled out of its joint. A patch will not change a fall. We re-firr or use tapered insulation so water runs away from the wall, then form a new upstand, usually 150 mm above the finished roof, with a flashing chased into the mortar joint.
Rooflights and lanterns are the other weak point. A lantern needs a properly built kerb with the membrane dressed up and under its frame. We rebuild rooflight upstands within the roof job; we do not supply the lantern itself. Our guide to ponding water explains the causes in more depth.
What's included?
- New abutment upstand and flashing, plus rebuilt rooflight kerbs
- Free survey of the roof, abutment and room below
- Staged strip-out so the room stays weathertight
- Building control handled where needed, and a written workmanship guarantee
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?
- Wellingborough · 9 mi
- Daventry · 12 mi
- Rushden · 12 mi
- Kettering · 12 mi
- Newport Pagnell · 13 mi
- Milton Keynes · 15 mi
Extension and kitchen roofs in Northampton: questions
Do you cover Northampton?
Yes. Northampton is part of our Northamptonshire coverage, including postcode districts NN1, NN2, NN3, NN4, NN7. 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 Northampton?
Where the work needs approval it goes to West Northamptonshire 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 new extension roof cost in Northampton?
£2,750–£4,800 for a 20 m² extension roof in EPDM with a new deck and insulation, at East Midlands guide rates including VAT. The fixed price comes after a free survey for new and replacement roofs.
How do I know my extension roof needs replacing rather than repairing?
Repeated leaks, a soft deck, wet insulation or widespread cracking point to replacement. A single defect on a dry, sound roof can usually be repaired.
Do I need my neighbour's permission to replace an extension roof?
Not for a like-for-like re-cover in most cases. The Party Wall Act in England and Wales can apply if the work raises or cuts into a shared wall, so we flag that at survey.