Cut Roof Carpentry for Extensions in Southampton and Eastleigh

Most single and two-storey extensions around Southampton and Eastleigh end up with a cut roof rather than factory trusses. The reason is simple: an extension has to meet an existing house, and existing houses are rarely square, level or standard. A cut roof is built on site from loose timbers, measured and cut to fit, which lets a carpenter deal with whatever the original building throws up. Here is what that involves and what to think about before your roof goes on.

Why extensions usually get a cut roof

Trusses work well on a new build where every wall is set out from scratch. On an extension, the new roof has to line up with an old wall, an existing eaves height and often a roof pitch that was set decades ago. Even a few millimetres out over the length of a wall makes a pre-made truss awkward to fit, and changing it on site is not allowed without the manufacturer's say-so.

A cut roof gets around that. Rafters, ridge, wall plates and hips are cut to suit the actual building, so the new roof can match the old pitch and sit neatly against the house. It also leaves the loft space open, which matters if you want vaulted ceilings, rooflights or storage. If you are new to the terms, our guide on what a cut roof is covers the basics, and the roof is part of the wider first fix carpentry stage on any extension.

Common extension roof styles locally

The housing around Southampton and Eastleigh is a real mix: Victorian and Edwardian terraces in areas like Shirley and Portswood, inter-war semis, and plenty of post-war and 1970s estates. That variety shows up in the roof styles we see on extensions:

• Lean-to roofs on single-storey rear extensions, with rafters fixed to a wall plate bolted to the house and pitched down to the new eaves.
• Gable-ended roofs, often on side or wraparound extensions, where the new ridge runs out from the house.
• Hipped roofs on two-storey side extensions, chosen to match a hipped main roof on many semis.
• Valleys and tie-ins where the new roof meets the old one, which is where most of the skill and time goes.

Your architect or designer will set the style on the drawings, and the structural engineer will specify timber sizes and spacings. The carpenter's job is to turn those drawings into a roof that fits the building in front of them.

Tying the new roof into the old

The tie-in is the part that makes or breaks an extension roof. On older terraces the existing walls can lean, the eaves may dip, and the original rafters are often smaller than modern timbers. Before cutting anything, a good carpenter will check the existing levels and pitch, and work out how the new ridge and valleys will meet the old roof without creating dips or awkward junctions for the roofer.

Where a valley is needed, the old roof covering is stripped back locally and valley boards or lay boards are fitted so the new rafters can sit over the existing ones. Wall plates are bolted or strapped down, and restraint straps are fixed to meet building regulations. Getting this right at first fix saves a lot of trouble later with tiling, leadwork and leaks.

Building control, engineers and timings

Building control will want to see the roof structure before it is covered up, so expect an inspection once the carcass is complete. They will check timber sizes against the engineer's calculations, strapping, bearing points and any steel beams where openings have been made into the house. It is worth having those calculations on site from day one.

As a rough guide, the carpentry on a simple lean-to over a single-storey extension can take a couple of days, while a hipped two-storey roof with valleys into an existing roof can take a week or more. Every job differs, and weather plays a part, especially with the wet, windy spells the south coast gets through autumn and winter. Timber is usually ordered once the walls reach plate height so sizes can be confirmed against the actual build. For a wider view of how the roof fits into the whole build, see our first fix timeline for extensions, and for costs, our guide to cut roof costs in Hampshire.

Planning your extension roof with PRM Carpentry

If you are planning an extension in Southampton, Eastleigh or the surrounding villages, it pays to bring the carpenter in early. A quick look at the drawings and the existing house can flag tie-in problems, timber lead times or design tweaks before the builder reaches plate height. Phil handles cut roofs, floor joists, stud walls and the rest of the structural timberwork as part of our first fix carpentry service across Hampshire. Get in touch for a free, no-obligation quote and an honest view of what your roof will involve.