Dormer Carpentry: Cheek Framing & the Structural Roof Opening

The cheeks are the two vertical side walls of a dormer, running from the new flat or pitched dormer roof down to where it meets the main roof slope. Cheek framing means building a small stud structure for each side, set out square and plumb to the approved drawings, then tying it back into the trimmed rafters either side of the structural opening. The cheeks carry the dormer’s own roof and front wall, so they need to be framed correctly before anything above them goes on.

We trim and double the rafters either side of the opening first, and fit new trimmer timbers across the top and bottom of where the opening will be, so the load that the cut rafters were carrying is transferred around the opening before any timber is actually removed. Only once that trimmed structure is in place and checked do we cut away the redundant section of roof. The sequence, and the size of trimmer needed, follows the structural engineer’s or architect’s design for the specific dormer.

The trimmed rafters at the sides of the opening are doubled up and fixed back to sound existing rafters, and the dormer cheeks and front wall are framed off that trimmed structure rather than simply built on top of the roof covering. Done properly, the dormer becomes a structural extension of the existing roof, carrying its own loads down into the trimmers and the rafters either side, rather than a box that is merely weatherproofed onto the slope.

We frame flat-roofed dormers, pitched (gable-fronted) dormers, and hipped dormers, following whichever design has been approved on your planning drawings. The framing principles are the same in each case — trim the opening, frame the cheeks and front wall, build the dormer’s own roof structure — but the roof shape above the cheeks differs, and the planning consent will usually specify which one applies to your property.

Yes. Dormer dimensions, position on the roof slope, and sometimes materials are frequently conditions of the planning permission or permitted development allowance, and building a dormer larger or in a different position than consented can put the whole conversion at risk with the local authority. We frame strictly to the approved drawings and flag it immediately if anything on site makes that difficult to achieve.

They overlap but are not identical. Cut roof carpentry is the wider discipline of building or altering a roof structure rafter by rafter on site; dormer carpentry is the specific job of cutting a structural opening into an existing or new cut roof and framing the dormer itself. A dormer is usually formed within a cut roof, which is why we cross-link closely to our cut roofs and roof carpentry pages — for the fuller technical picture of the roof structure a dormer ties into, those pages go deeper on rafters, hips and ridge beams generally.

No. We cut the structural opening, frame the cheeks and front wall, and build the dormer’s small roof structure in timber. Felt or membrane, battens, tiles or slates, leadwork and flashing, external cladding, and the window itself are separate trades that follow our structural carpentry — usually a roofer, a leadworker or cladding installer, and a window supplier. We are happy to recommend contractors we have worked alongside for each.

We carry out dormer carpentry across Berkshire, Surrey and South Buckinghamshire, including Ascot, Bracknell, Windsor, Maidenhead, Reading, Wokingham, Sunningdale, Virginia Water, Camberley, Stoke Poges and Gerrards Cross.