Cut Roof Carpentry — Built Rafter by Rafter, Not Lifted Into Place

A trussed roof arrives on site as prefabricated triangular frames, lifted into place by crane in a day and designed for a simple, standard roof shape. A cut roof is built rafter by rafter, on site, to the engineer’s or architect’s design — every rafter, hip, valley and ridge is set out and cut individually. That on-site flexibility is the whole point of a cut roof: it can tie into an existing roofline, step around a chimney, or carry a dormer, in a way a factory-made truss cannot.

Almost every extension and loft conversion needs a cut roof, because the new roof has to tie into a roofline that already exists and was never built to a standard truss geometry. Trusses need a clear span and a straightforward shape decided before manufacture; a cut roof is the only practical route where there are dormers, rooflights, hips, valleys, changes in pitch, or a period roofline with no two sides quite the same. If your project touches an existing roof in any way, assume it will be a cut roof.

Cut roof carpentry is more labour-intensive than fitting prefabricated trusses, because every rafter is set out, cut and fixed individually on site rather than arriving ready-made. For a genuinely simple new-build roof with a clear span and no complications, trusses can work out cheaper. But for extensions, loft conversions and period properties — where the roof has to match an existing structure — a cut roof is not really a cost choice against trusses; it is the only method that will physically work, so we price it on its own terms rather than against a truss alternative that was never viable.

Yes — that is the main reason a cut roof is specified. Hip and valley junctions, where two roof slopes meet at an angle, and dormer openings, where a section of the main roof is cut away and reframed, both need timber set out and fixed to match the exact geometry on site. Trussed roofs are built around a fixed, repeated frame shape and struggle to accommodate this kind of local variation without a cut roof section built in alongside them.

A trussed roof can go up in a day once the trusses are delivered, because the frames arrive finished. A cut roof for a single-storey extension typically takes a roof carpentry team three to six days, longer where there are hips, valleys or a dormer involved — because every member is set out and cut on site rather than lifted into place. The trade-off is flexibility: a cut roof takes longer to build but can do things a truss roof physically cannot.

We build to a structural engineer’s or architect’s design; we do not design roof structures ourselves. If you do not yet have a design, we can recommend engineers we have worked alongside, but the structural calculation and drawing need to come from a qualified designer before we price or start cutting timber.

In almost all cases, yes. Cut roof construction and structural alterations to an existing roof fall under Building Regulations Part A (structure) and are inspected by the local authority or an approved inspector before the structure is covered. We leave the roof accessible for that inspection and build to the standard the engineer’s design specifies.

Yes — period properties are one of the clearest cases for a cut roof. Older roofs are rarely symmetrical or built to a standard pitch throughout, and a new section has to be individually set out to match what is already there rather than built from a repeated factory frame. We measure the existing roofline on site and cut the new structure to tie into it, working to the engineer’s design for the new section.