Bulkhead Calculator — Timber Frame, Board & Access Panels

For most domestic bulkheads, 44 × 44mm planed (PAR/PSE) timber — the finished '2×2', planed down from 50 × 50mm nominal — is sufficient. (This is planed softwood, not CLS; true CLS is 38 × 63mm or 38 × 89mm with rounded arrises and is an equally valid alternative.) For larger bulkheads (over 300mm in any dimension) or those carrying weight (e.g. supporting a shelf), use 44 × 69mm or 44 × 94mm timber. The frame must be securely fixed to the wall and ceiling with appropriate fixings — rawlplugs and screws into masonry, or directly into timber studs/joists.

Standard 12.5mm plasterboard is suitable for most bulkheads. In bathrooms or high-moisture areas, use moisture-resistant (green) board. If the bulkhead conceals gas pipes, use standard board but ensure access panels are provided for inspection. Fix 12.5mm board into the timber frame with 38mm coarse-thread (W-type) drywall screws — these give about 25mm timber penetration, whereas 32mm screws (intended for 9.5mm board or board-to-metal) leave only ~19.5mm. A bulkhead is an encasement, so screw at roughly 150mm centres throughout, keeping fixings at least 10mm from bound edges and 13mm from cut edges (British Gypsum encasement fixing guidance).

Yes, if the bulkhead conceals isolating valves, joints, inspection points or any serviceable fittings. Building Regulations and Water Regulations require access to stopcocks and isolation valves. For gas pipes, access must be provided at every joint. Use push-fit or spring-loaded access panels in standard sizes (150×150mm, 200×200mm, 300×300mm). Tile-on-frame panels are available for tiled bulkheads.

Build a timber frame with top and bottom rails fixed to wall and ceiling, vertical uprights at each end and noggings at 400mm centres. Fix plasterboard to all three exposed faces (front, bottom soffit and any visible side). Tape and joint all board edges, including internal corners. For a neat finish, use external corner bead on the visible edges before skimming or painting.

Measure the run length and multiply by the number of framing rails (typically 2-4 depending on type). Add noggings at 400mm centres: count the number of bays and multiply by the nogging length (drop height + projection for box sections). For an L-shape or box bulkhead each noggin frames both faces, so use (drop height + projection) per noggin; for a soffit-only run use the projection alone. Add 10-15% for waste and end cuts. Standard 2.4m lengths of 44 × 44mm planed (PAR) timber are most economical for typical domestic work.