What Size Timber for a Stud Wall? 3×2 vs 4×2 CLS Explained

The inch labels are trade names associated with the timber before finishing, not the dimensions to enter into a finished-wall calculation. Planing and eased corners reduce the section. Buy against the merchant's stated finished size and check the supplied timber.

Specifications checked on 13 October 2026: Wickes lists CLS products 107177 and 107713 at 38 × 63 × 2400mm and 38 × 89 × 2400mm respectively. Both are described as C16 graded and kiln dried. Product lengths and grades vary; C16 on its own does not approve the whole partition.

Add the stud depth to the lining thickness on both sides, then include any finishes or additional layers. The arithmetic below is dimensional only: it does not establish fire, sound, impact or height performance.

Studs normally present the 38mm face to the boards, with the 63mm or 89mm dimension across the wall. Do not rotate them simply to squeeze the wall into a smaller space; that changes the specified framing arrangement.

British Gypsum's A026010 (EN) timber stud partition specification, checked on 13 October 2026, is a concrete example of a specified non-loadbearing system. It uses 63 × 38mm timber at 600mm centres, one layer of 15mm Gyproc WallBoard each side and 25mm Isover APR 1200 in the cavity.

That exact specification lists 93mm partition thickness, a maximum height of 4000mm, 30-minute fire integrity and insulation, and 40dB airborne sound insulation Rw. Those are declared properties of the complete specified assembly, not generic claims for any 3×2 wall. Laboratory Rw is not a guarantee of the sound reduction achieved between two completed rooms.

The same specification identifies 40mm British Gypsum drywall screws, sealant and fixing details, including maximum board-fixing centres. Changing board type or thickness, screws, insulation, stud spacing, perimeter sealing or junction details can invalidate the claimed performance. Do not substitute a generic accessory from an affiliate card for the specified component.

This example shows why neither 'always use 400mm centres' nor '3×2 is only suitable up to this height' is a reliable universal rule. Use the manufacturer system that meets the actual job, follow all its details and confirm any Building Control requirements.

A 63mm section can be appropriate where the selected non-loadbearing system covers the height, lining and required performance and leaves enough space for the services. It reduces the wall footprint compared with 89mm framing with identical boards.

An 89mm section provides 26mm more gross cavity depth, which can help when the specified insulation, service arrangement or fixing detail needs that room. It is not automatically better acoustically, and it is not permission to drill larger holes, hang heavier loads or support a floor.

Door openings, pocket-door frames, wall-mounted fittings, tiled faces and heavily used partitions need their own details. Provide the specified noggins or other support for fixtures, and confirm the loading with the system or fixture manufacturer. If the wall may be loadbearing, stop using a non-loadbearing sizing guide and obtain a structural design.

The 63mm or 89mm dimension is a gross cavity depth. Timber studs interrupt that space, and pipes, cables and electrical boxes need their own routes, fixings and clearances. A pipe that fits between studs is not automatically safe to run through them.

Plan service routes before specifying timber. Do not improvise holes or notches without the applicable framing or system guidance; avoid unnecessary cuts and deal with penetrations, fire stopping and acoustic sealing as required. Electrical work must follow the relevant installation requirements.

Use the insulation type and thickness in the chosen partition specification. For example, A026010 uses 25mm APR in a 63mm cavity, not a requirement to stuff the whole cavity full. Loft rolls, rigid PIR and acoustic partition products are not interchangeable simply because they fit.

Sound performance also depends on the boards, junctions, air paths and workmanship. A deeper stud with unsealed gaps can disappoint, while a properly detailed specified shallower system can meet its intended performance.

Illustration only: a straight 3m-long internal partition, with one 12.5mm board and an assumed 2mm skim on each face. Ignore door openings and other finishes for this dimensional comparison. This is not approval of either assembly.

The 63mm framing option totals 92mm; the 89mm option totals 118mm. The difference is 26mm, or 0.026m. Across a 3m wall, the difference in floor footprint is 3 × 0.026 = 0.078m².

That is a modest space trade-off, not a reason to ignore services or performance. Choose the compliant build-up first, then measure door linings and room dimensions. Only then calculate studs, plates, noggins and sheets.

Buy the actual finished section, grade, stock length and condition required by the selected system. A category page lets you compare products; it does not verify that every listed timber or board meets your wall specification.

A metric tape, suitable timber handsaw and short spirit level can help with measuring, cutting and local alignment. They do not establish stud size, full-wall plumb or structural adequacy. Check for buried services before fixing plates or drilling.

Keep the distinction between design and quantities: the timber quantity guide explains the components to count; the Stud Wall Calculator and Plasterboard Calculator estimate material quantities, not system compliance.