How to insulate a stud wall

Inspired by a helpful guide from TradePoint. This walk-through draws on the "How to insulate & plasterboard a stud wall" video from TradePoint (B&Q's trade brand), which covers the whole process clearly - from fitting the first sheet of plasterboard through to closing the wall up. The section on fitting insulation without compressing it is particularly useful and worth paying attention to.

1. Locate and mark the studs

Before anything else, know where your studs are. Use a stud finder or knock along the wall - a solid sound means stud, a hollow sound means cavity. Mark each one in pencil.

Standard stud spacing in UK homes is 400 mm or 600 mm centre-to-centre, but older properties can be more erratic. Measure carefully before ordering insulation and plasterboard.

2. Choose your insulation

Mineral wool batts (often sold as Rockwool or Knauf Earthwool) are the most common choice for stud walls. They're cheap, effective, and cut easily with a bread knife or a sharp blade.

Buy batts that match your stud depth. Most UK stud walls use 75 mm or 100 mm timber, so 75 mm or 100 mm mineral wool is usually the right fit. PIR (rigid foam) boards are an alternative if you need better performance in a thinner profile, but they cost more and need more precise cutting.

3. Fit plasterboard to one side first

If the wall is open on both sides, board one face completely before you start insulating. Fix 12.5 mm plasterboard to the studs using drywall screws, keeping screws 150 mm apart along each stud.

Make sure the board joints fall on the centre of a stud. Mark the stud positions on the floor and ceiling first so you can find them once the board goes up. Much easier than trying to locate them afterwards.

4. Cut mineral wool batts to length

Measure the height of each stud bay - from sole plate to head plate - and cut the batts to that measurement. A long bread knife or a serrated blade works well. Score and compress, then cut through.

Cut the batts very slightly wider than the bay width as well - perhaps 10–15 mm wider. That slight compression around the edges holds them in place without any fixing, and gives a good seal at the sides.

5. Fit the insulation without compressing it

Push each batt into its bay and press it flat. It should sit flush with the face of the studs. This is the bit most people get wrong. Squashing or folding the batts significantly reduces their thermal performance - the air pockets trapped in the fibres are what actually insulate, and you lose them if the wool is compressed.

If a batt doesn't sit flat, trim it slightly rather than forcing it. A snug friction fit is exactly right.

6. Work around pipes and cables

Split batts around any pipes or cables running through the wall. Slide one half behind the pipe and one half in front, so the pipe is completely encased in insulation. Never cut a notch and leave a gap - that gap will become a cold bridge.

For electrical cables, make sure you understand the regulations before closing the wall. If you're unsure, speak to a qualified electrician before boarding up.

7. Fit the second layer of plasterboard

Once all the insulation is in, fix the second face of plasterboard. Again, 12.5 mm board on the studs with drywall screws at 150 mm intervals. Stagger board joints so they don't align with those on the opposite face.

Keep the boards tight to each other at the joints but don't force them. A small consistent gap of 2–3 mm is fine and actually preferred for taping.

8. Tape, joint, and finish

Apply jointing tape over all the seams and cover with jointing compound in thin coats, feathering the edges. Allow each coat to dry fully before applying the next. Two or three thin coats will give a much better result than one thick one.

Once it's all dry and sanded smooth, the wall is ready for a mist coat of watered-down emulsion followed by your chosen paint. To be fair, the finishing takes longer than the insulating - but that's the part that makes it look professional.

When to call a handyman

If the wall involves cutting around existing electrics, relocating sockets or light switches, or you're not confident with plasterboard finishing, Richard can step in. Stud wall insulation and plasterboarding is a regular part of his work, and he'll get it done tidily without leaving a mess for you to deal with.