A Partition with a Door, a Window and 25 kg Tool Boards
A 4.2 m long, 2.4 m high stud partition is to divide a technology room from a new store. The specification is 100 x 47 mm CLS studs at 600 mm centres, 12.5 mm plasterboard both sides, one 900 x 2100 mm door, and an internal glazed panel 1200 mm wide x 1000 mm high so staff can supervise from the store side. The ceiling is a proprietary suspended grid at 2.7 m with mineral fibre tiles; the structural soffit is 400 mm above the grid. The floor is a power-floated screed over slab. On the store side, two rows of tool boards are to be hung - each board 600 mm wide and loaded to about 25 kg - at 1000 mm and 1600 mm above floor level. The store also needs to be reasonably quiet because a dust extractor sits in one corner.
1. Set out the order of work for erecting this partition and explain why the head plate cannot simply be fixed to the suspended ceiling grid.
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Order of work:
- Mark the floor line from the finished face of the existing wall, using a chalk line and checking the diagonal to confirm squareness to the room.
- Transfer the line to the structural soffit with a plumb line or laser, displacing ceiling tiles and grid as needed; the grid must be temporarily supported while tiles are out.
- Fix the floor plate (with a DPC strip on the screed), then the head plate.
- Set out stud positions from the openings, not from the end - the door and window positions are fixed by the brief, and board edges must land on studs.
- Cut and fix studs 5-10 mm short, then form the door and window openings with trimmer studs and head pieces.
- Install noggins at board edges, then first-fix any services before boarding.
- Board one side, add insulation or acoustic quilt, board the other side, tape and skim.
Why not the grid? The grid is designed to carry ceiling tiles and light services, not the dead load of a partition, its boards, the door leaf and the swing force every time the door is slammed. Fixing to it would also couple the partition to the ceiling, transmitting machinery noise and cracking the tile joints. The head plate must go to the structural soffit, with a deflection detail if the soffit is a concrete slab that moves; if the soffit were a timber floor above, noggins between joists would be required.
2. Describe what is required over the door and the internal window, and how the glazed panel affects stud spacing and boarding.
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Door opening. The studs over a 900 mm door are cut away, so the load path must be restored: a head piece (a doubled 100 x 47 laid flat, or a purpose-made header) spans between trimmer studs on each side, with the trimmer studs fixed back to the adjacent full studs. The plasterboard edges above the door need support, so the head piece must be positioned to give a board joint with timber behind it. The door lining or frame is fixed to the trimmers, checked plumb and square, before boarding.
Internal window. Same principle: trimmer studs both sides, a head above 1000 mm, and a sill piece below. If the sill is at, say, 900 mm, the sill member must be stiff enough not to sag under a hand or a leaning file - a 100 x 47 on edge, or a doubled flat plate.
Effects on setting out:
- Stud centres at 600 mm are a module, but the window and door positions break it; the setting-out drawing must show every stud, not just 'at 600 c/c'.
- 12.5 mm board on 600 mm centres is at its span limit for a wall that will take knocks from a technology room - consider 400 mm centres or 15 mm board.
- For the noise from the extractor, the cheapest effective steps are mineral wool full-fill in the cavity and careful sealing of the perimeter with acoustic mastic; staggered studs or resilient bars improve it further at extra cost.
3. Explain how the 25 kg tool boards should be supported, and what you would change if the boards were heavier or the partition were only 75 mm deep.
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First, do the load check. 25 kg is about 250 N hanging on a lever arm of perhaps 100 mm, so the pull-out force at the top fixing is well beyond what a plasterboard plug in 12.5 mm board will hold reliably - and the board is only as strong as its fixing to the studs behind it. Hanging directly on plasterboard is the wrong answer.
Correct approach:
- Fix an 18 mm plywood pattress, at least the height of the two board rows, spanning two studs, behind the plasterboard at the layout stage. Mark stud and pattress positions on the finished wall or record them on the drawing.
- Screw the tool boards through the plasterboard into the pattress or directly into studs with at least four screws per board, into two separate studs where possible.
- Use a French cleat or rail system so the load is spread along the wall and boards can be rearranged without new holes.
If heavier: design the pattress into the frame as a ladder of noggins and ply, and check the studs and fixings for the combined load; consider a floor-to-ceiling ply lining in that bay.
If only 75 mm deep: the frame is slimmer and less stiff; keep 600 mm centres at most, avoid cutting the studs more than necessary, and if the load is significant, add a dedicated vertical member taken down to the floor plate rather than hanging everything off the plasterboard line.