What timber size should I use for a bulkhead frame?

For most domestic bulkheads, 44 × 44mm (2×2 inch) CLS timber is sufficient. 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.

What type of plasterboard should I use for a bulkhead?

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. Plasterboard must be fixed with 32mm drywall screws at maximum 300mm centres on the face and 150mm at board edges.

Do I need access panels in a bulkhead?

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.

How do I build a box section bulkhead?

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.

How do I calculate the amount of timber for a bulkhead?

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). Add 10-15% for waste and end cuts. Standard 2.4m CLS timber lengths are most economical for typical domestic work.

Bulkhead Calculator — Timber Frame, Board & Access Panels

Calculate timber framing, plasterboard and access panels for bulkheads and boxing around pipes, ducts and structural elements.

Run Length

Length of the bulkhead run

Drop Height

Vertical face height

Projection Width

Horizontal soffit width

Bulkhead Type

Box section for freestanding pipe runs

Include access panel(s)

Required for valves, joints and serviceable fittings

Timber Price (optional)

Per 2.4m CLS timber

Board Price (optional)

Per 1200×2400mm board

Access Panel Price (optional)

Per access panel

How We Calculate This

This calculator determines the timber framing, plasterboard and access panels needed for building a bulkhead or pipe boxing.

The formula

Timber = Perimeter frame rails + Noggings at 400mm centres

Board area = Run length × Face dimensions × Number of faces

For a 3m box bulkhead (200mm drop × 150mm projection): frame rails ~3 × 4 = 12m, noggings = 8 × 0.35m = 2.8m. Board = 3 × (0.2 + 0.15 + 0.2) = 1.65 m².

Bulkhead types

Box section: 3 visible faces — most common for pipe runs
L-shape: 2 visible faces — where bulkhead meets a wall corner
Soffit only: 1 face — horizontal only, e.g. above kitchen units

Frequently Asked Questions

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Last updated: March 2026

All calculations are estimates. Verify with your supplier.