Stud and framed partition

Frequently asked questions

Why is a 2x4 not two inches by four?

Because it was, before it was planed. Timber is sawn to the nominal size green and then dried and surfaced, and both take material off — so a nominal 2x4 finishes at about 1½ by 3½ inches, a 2x6 at 1½ by 5½, and the nominal figure survives as a name rather than a measurement. British practice has the same phenomenon with an extra wrinkle: timber is sold both SAWN and PLANED, and a 'four by two' regularised for framing is typically around 38 by 89 mm — which is the same finished section as an American 2x4 by a different route, since 38 by 89 is 1½ by 3½ inches converted. So the two markets nominally disagree and physically arrive at the same stick. What does not travel is the assumption: a specification quoting a nominal size has not stated a dimension, and a specification quoting millimetres usually has.

What are king, jack and cripple studs, and what does British practice call them?

They are studs named by their job at an opening, and British practice mostly has no equivalent words. A KING stud runs full height beside an opening; a JACK or trimmer stud is the shorter one nailed to it that carries the header or lintel; a CRIPPLE is a short stud above a header or below a sill, filling the gap at the normal spacing so the covering still has a fixing. British drawings tend to describe the same arrangement geometrically — a full-height stud each side with a trimmer under the lintel and short studs over — without naming the members. The consequence when reading American framing guidance is that the count matters: a specification calling for two jacks each side is calling for four extra studs per opening, and that is not a detail a British take-off derived from a stud spacing will have picked up.

Why is stud spacing 400 or 600 mm rather than anything else?

Because the BOARD decides it, not the stud. Plasterboard and sheathing come in fixed widths — 1200 mm, or 4 feet — and every sheet edge has to land on a member. Divide 1200 by 400 and you get exactly three bays with an edge on a stud at each end; divide by 600 and you get two. That is the whole reason those two numbers dominate: they are the divisors of the sheet, and 16 and 24 inches are the same two numbers in the other system. The structural question — whether a stud of a given size can carry the load at that spacing — is then checked against the spacing the boards imposed, rather than the other way round. It is also why a non-standard spacing costs more in board than it saves in timber: every sheet needs cutting and the offcut is usually waste.