Start on the floor and work up to the ceiling
Everybody wants to mark the ceiling first because the ceiling is the awkward one. Do the floor. The floor is the line you can see, kneel on and adjust, it is where the door position is decided, and it is the only one of the two you can chalk a straight line on without a second pair of hands.
Snap the line, lay the sole plate on it, then transfer that line to the ceiling with a spirit level held against a straight edge at each end, or with a plumb bob, or with a laser if you have one. Mark both ends up there, join them, and check the two plates are the same length before either is fixed. If they are not, something is out of plumb and it is far cheaper to find that now.
A wall built flat will not stand up in the gap it was cut for
This is the one that catches people, and it catches them at the worst possible moment, holding two and a half metres of timber at forty five degrees in a bedroom.
When you tilt a wall upright it turns about its bottom edge, so the corner diagonally opposite that edge travels on an arc. The radius of that arc is not the height of the wall, it is the diagonal across the wall's section, and the diagonal is always the longer of the two.
A 2400 wall built from 75mm studs has a section diagonal of 2401.2mm, so it wants 2401mm of headroom in a 2400mm gap. Go to 100mm studs and it wants 2402. It is a small number and it is the wrong side of zero, which is all that matters when the wall is in your hands.
So either build it in place, fixing both plates and cutting the studs to fit between them, or build it flat about 15mm short and pack the head plate up to the ceiling once it is standing. The second one is quicker and the packing is not a compromise: it is how you get a wall plumb against a ceiling that is not level.
The head plate needs something to bite into
Fixing the sole plate is rarely a problem. The head plate is, and it depends entirely on which way the joists above happen to run.
- Across the wall line. The easy case. The plate crosses joist after joist and you screw up into each one.
- Along the wall line, and lucky. The wall lands directly under a joist, so you fix into that joist for its whole length.
- Along the wall line, and not lucky. The wall lands in the gap between two joists and there is nothing up there but plasterboard. This is the one that stops the job.
In the third case the honest answer is that noggins have to go in between the joists above, at roughly a metre apart, for the plate to fix to. From above if there is a loft or a liftable floor, and from below through a cut strip of ceiling if there is not. Fixing a head plate to plasterboard alone is not a wall, and it is the fault that produces the crack along the ceiling that keeps coming back after every decoration.
Working out which way the joists run is the same problem the joist explainer covers, and the short version is that floorboards run across joists and the fixing lines in the ceiling give the rest away.
Nothing in an old room is square, so every stud is its own measurement
New-build partitions get cut in a batch because the floor and ceiling are parallel. In a house that has been standing eighty years they are not, and a batch of identical studs produces a wall that is tight at one end and 6mm short at the other.
Measure each stud position between the fixed plates and cut that one to that measurement. It feels slow and it is about ten minutes across a normal wall. Cut each one a whisker long so it goes in under tension and stays where it is put while you fix it, and check plumb on every third or fourth one as you go, because a wall that has drifted is only fixable while most of it is still unfixed.
Once the positions are set, the stud wall calculator gives the count and the noggin lengths, including the extra stud at the end that gets missed, and the timber quantity tool turns the cut list into lengths to buy.
Leave the sole plate running through the doorway
Fix the plate straight across the opening as though the door were not there, build the wall, then cut the plate out between the two door studs with a handsaw at the end.
Two reasons, and the second is the real one. The plate keeps the bottoms of the door studs at the right spacing while you are working, so the opening ends up the width you set rather than the width it drifted to. And a wall with a gap in its bottom plate is a wall in two halves until the head is fixed, which makes the whole thing wander as you push against it.
Before the boards go on
The wall is at its most useful in the ten minutes before it gets closed up, and everything on this list is expensive afterwards.
- Services in and tested. Cables and pipes through the studs, sockets and switch boxes fixed, and anything that runs water put under pressure before a board goes near it.
- Noggins where fixings will land. Behind the radiator brackets, behind the TV, behind a rail, behind a basin. You are guessing at the future here and a spare noggin costs nothing.
- Insulation in. Mineral wool between the studs, for sound rather than for heat on an internal wall, and it is the best value thing you will do all day.
- A photograph of every bay. One picture on your phone before boarding tells you where every cable runs for the next thirty years, and it is the only record that will ever exist.
Then the boards, which the plasterboard calculator covers along with the fixings and the scrim, and the rule that decides the layout: every board edge lands on a stud, or the joint cracks.
Common questions
Should I build it flat on the floor and tilt it up, or build it in place?
In place, for almost any wall that reaches the ceiling. Tilting up is faster and it is how new-build partitions go in, and it only works where there is headroom to swing the wall through, which inside a finished room there generally is not. If you do want to build it flat, make it about 15mm short of the ceiling, tilt it, then pack the head plate down onto the ceiling and fix through the packers. Building in place means fixing both plates first and cutting the studs to fit between them, which is slower and much more forgiving.
What size timber do I need?
For a non-loadbearing partition in a house, 75 by 50 is the usual choice, and 100 by 50 where you want depth for pipes or for sound. Planed CLS comes in at slightly under its nominal size, so 4 by 2 CLS is nearer 63 by 38, and the difference matters when you are working out how much floor the finished wall eats. Deeper studs are the cheapest acoustic upgrade there is, and the decision has to be made before the layout is fixed, because 25mm of extra depth comes off the room.
How do I fix the sole plate to a concrete floor?
Hammer-in frame fixings through the plate into the slab, at roughly 600 centres and within about 150mm of each end. Drill the timber and the concrete in one go with the plate held on the line, which keeps the holes true. On a suspended timber floor you want the fixings landing in joists wherever you can reach them, and where the wall runs parallel to the joists and lands in a gap, the plate is fixed to the boards and the wall gets its real stability from the head plate and the ends.
Do the noggins go in a straight line across the wall?
Stagger them, by about the depth of the noggin, unless you have a reason not to. A straight line looks tidier and it leaves you unable to drive a nail or a screw straight through the stud into the end grain of both neighbours at the same height. Staggering means every noggin gets fixed properly through the stud from the side. The exception is a noggin line that has to be straight because it is carrying something across several bays, like a run of rail or a heavy bracket, and then you fix through skew instead.
Should the wall be tight to the ceiling or is a gap alright?
Tight, and packed if it is not. A head plate with a gap behind it flexes every time somebody shuts a door, and that movement cracks the tape line along the ceiling within a year. Packers are not a bodge here, they are the fix: the ceiling is not flat, so a plate that touches at one end and stands 4mm off at the other is normal, and slate or plywood packers driven in before you fix through are what makes it solid.
Do I need building control for a partition wall?
Usually not for the wall itself, and the thing that pulls one in is what the wall creates rather than the wall. Dividing a room can leave a space with no window, no ventilation or no way out in a fire, and any of those is a genuine question for your local building control office before you start rather than after. A partition that simply splits a large room and leaves both halves with their own window and their own door is the ordinary case, and it is the case most people are in.