Once you have decided to build an extension on your Birmingham or Solihull home, one of the first big design decisions is the roof. Flat or pitched? Each has very different implications for cost, light, planning and finish. Here is a straightforward comparison based on what we at CK Construction actually build week in, week out.
The quick version
- Flat roof: Lower cost, lower profile, great for roof lanterns and large skylights, usually within Permitted Development.
- Pitched roof: Longer lifespan on a traditional house, matches the main building, more work and more cost, often needs full planning.
Flat roofs on extensions
Modern flat roofs are nothing like the bitumen pond roofs of the 1970s. A warm-roof build-up using GRP fibreglass or EPDM single-ply membrane, with 150mm of PIR insulation above the deck, now carries a 25-year guarantee and performs well above current Building Regs for U-values.
Where flat roofs excel
- Keeping within Permitted Development. Flat roofs on a single-storey rear extension have a maximum height of 4m from original ground. That makes them the default choice when you want to avoid a full planning application.
- Roof lanterns and large glazing. A central roof lantern over a kitchen island is far simpler to detail on a flat roof.
- Modern aesthetics. A clean parapet detail with hidden gutters suits contemporary rear extensions on 1930s semis and Victorian terraces alike.
Pitched roofs on extensions
A pitched roof on an extension typically costs 20-40 per cent more than a flat roof of the same floor area. In return you get longer lifespan (50-80 years for clay tiles against 25-30 for a well-built flat roof), better matching to the host property, and extra ceiling height inside.
Where pitched roofs excel
- On side extensions where you want the ridge line to continue off the existing roof.
- On wrap-around extensions that are visible from the front of the property.
- On conservation areas and listed buildings where planners expect a traditional roof form.
Can you combine them?
Yes, and we often do. A pitched roof over a side return feeding into a flat section with a central lantern over the rear kitchen gives you the best of both: planning-friendly massing to the side, maximum rooflight over the open-plan space.
Our honest recommendation
For a typical single-storey rear extension on a semi in Edgbaston or a terrace in Moseley, a warm flat roof with a generous roof lantern delivers brilliant light, keeps the project within Permitted Development, and comes in at a sensible cost. For double-storey or front-visible extensions, a pitched roof matching the host property almost always looks better.
Talk to our team about your specific project. Call 01527 521835 or use the contact form.