Partition Height Calculator — Max Height by Stud Size per BS 5234

The maximum height depends on the stud depth, spacing, and number of board layers. Using the British Gypsum White Book (GypWall Classic, Table 2), a 70mm C-stud (Gypframe 70 S 50) at 600mm centres with a single 12.5mm board each side reaches 3600mm; a 92mm stud reaches 4500mm and a 146mm stud 6200mm in the same configuration. Adding a second board layer each side, closing the centres to 400mm or 300mm, or moving to a twin/staggered-frame system raises these figures further. For anything above 4.5m, step up to a 92mm or 146mm stud. All heights are quoted to a limiting deflection of L/240 at 200 Pa (0.2 kN/m²).

BS 5234 is the British Standard for internal non-loadbearing partitions. Part 1 (BS 5234-1) is the code of practice for design and installation; Part 2 (BS 5234-2) specifies the performance requirements for strength and robustness and defines the duty grades — Light, Medium, Heavy and Severe Duty (LD/MD/HD/SD). Manufacturers quote their maximum partition heights to a serviceability limit of L/240 mid-height deflection under a lateral pressure of 200 Pa (0.2 kPa), referencing BS 5234 stiffness testing. On that basis a 3m partition should deflect no more than 12.5mm (3000 ÷ 240). BS 5234 is a performance standard rather than a clause of the Building Regulations — specify the duty grade that suits the room’s use.

A deflection head allows the partition to accommodate structural movement (floor deflection, thermal expansion) without transferring loads to the partition. It is essential in all steel-frame and concrete-frame buildings where slab deflection can be 10-25mm. The stud sits in a deep track at the head with a compressible material allowing vertical movement. Without a deflection head, structural movement can crack the partition or buckle the studs.

Adding a second layer of plasterboard each side stiffens the partition and raises its limiting height. In the British Gypsum White Book, for example, a 70mm stud at 600mm centres goes from 3600mm with one 12.5mm board each side to 4600mm with two — roughly a quarter taller. The exact uplift varies by stud and centres, so read it from the manufacturer height table rather than applying a rule of thumb. Note the boards are screw-fixed (not bonded) to the studs, so they do not act as a true composite flange; the extra height comes from the added stiffness and mass measured in the manufacturer’s tests.

Timber studs (typically 38mm × 89mm or 38mm × 140mm) can be used for partitions, but their maximum heights are generally lower than steel C-studs of equivalent depth. Timber also has more variable properties and can twist, warp, or shrink. For partitions over 3m, steel C-studs are strongly recommended. BS 5234 covers both steel and timber stud systems.