Drywall partition· 4 min read
Double-Layer Drywall and Doors in a Partition: What Changes in Materials
One or two layers of plasterboard, CW or UA studs at the door and staggered joints: what changes in the materials for a 4 × 2.75 m partition with a door.
The frame is the same whether you board a partition with one layer or two. What changes is the number of boards, screws and filler, how the boards are screwed and how high the wall may be. At the door, the wall height and the width and weight of the door leaf decide whether ordinary CW studs are enough. Here's the same 4 × 2.75 m wall with a 900 × 2,050 mm opening.
One layer vs two
| Wall 4 × 2.75 m with door | 1 layer each side | 2 layers each side |
|---|---|---|
| Boards 1250 × 2750 mm | 8 | 16 |
| Board area | 18.31 m² | 36.62 m² |
| Screws | 275 | 403 |
| Filler | 4.6 kg | 7.3 kg |
| Joints of the outer layer | 14.45 m | 14.45 m |
| CW / UW lengths | 9 / 3 | 9 / 3 |
| Insulation | 9.15 m² | 9.15 m² |
Twice the boards, but not twice the screws. With vertical 1,250 mm boards Knauf screws the inner layer only every 750 mm — the outer layer then holds it — and the outer layer every 250 mm. That's about 7 screws per m² of inner layer and 15 per m² of outer. On our wall: 9.155 m² × 2 sides × 7 = 128 plus 9.155 × 2 × 15 = 275, 403 screws in total. The outer layer needs longer screws, as they go through both boards into the stud.
Filler: the joints of the inner layer are filled too, just not finished smooth. The calculator uses 0.15 kg per m² of inner and 0.25 kg per m² of outer layer, which for the wall without a door is exactly Knauf's 0.8 kg per m² of wall. Tape goes on the outer layer only, so the joint length stays the same.
Why two layers: a harder and stiffer surface, better sound insulation and fire resistance, and a taller wall on the same stud. Knauf's Swiss document W11.ch, for example, gives a maximum height of 3.20 m for CW 50 at 625 mm with one 12.5 mm board and 4.00 m with two. Check the heights for your system and country in the manufacturer's documents.
Drywall partitionOpen the wall with a door and two layersDoor studs: CW or UA?
Knauf, citing DIN 18340, accepts ordinary CW studs beside a door only when all of these hold:
- the wall is at most 2.60 m high,
- the door is at most 0.90 m wide,
- the door leaf weighs at most 25 kg.
Otherwise (and as Knauf recommends, always) the door gets UA profiles of 2 mm steel, preferably full height without splices, fixed to floor and ceiling with brackets at top and bottom. A heavier leaf needs a bigger UA: for doors up to 0.90 m Knauf allows up to 50 kg on UA 50 and 75 kg on UA 75. The lintel is made from UW track. In a double-stud wall (two rows of studs) doors always get UA — that is not the same as two layers of board.
Our wall is 2.75 m, so UA is needed with one layer as well as two, and the metric calculator shows a warning. For a 2.60 m wall with the same opening it shows none, but you still have to check the leaf weight yourself. The stud count is the same either way: of 9 full-height studs, 2 are door studs, plus a 685 mm piece above the lintel.
Joints around the door
- A vertical joint must not run along the edge of the opening, i.e. on the door stud. Knauf's drawings keep it at least 150 mm away and move it towards the middle over the lintel.
- With one layer, in our example side A has joints 200 and 150 mm from the door studs; side B has one at 1,875 mm, only 25 mm from the middle of the opening. The calculator warns when a joint is closer than 150 mm.
- A strip of board above the lintel narrower than 400 mm is allowed by Knauf only with room-high boards.
Staggered joints
- Long (vertical) joints of opposite faces and of the two layers are offset by at least one stud spacing and always sit on a stud. That's why the calculator starts side B and the second layer 625 mm along.
- End (horizontal) joints, when boards are shorter than the wall, are staggered by at least 400 mm within a layer (at least 1,000 mm for single-layer fire-rated walls) and, with two layers, by about 250 mm between the layers.
How much room-high boards help shows on the same wall without a door boarded with 1250 × 2600 mm instead of 2750 mm: 10 boards instead of 8, 24.5 m of joints instead of 16.5 m, and strips only 150 mm high at the ceiling or floor, which the calculator flags. At this height 2,750 mm boards are the better choice, if you can get and transport them.
Drywall partitionCompare with 2,600 mm boardsThe calculator handles quantities and layout, not structural design. Stud size, spacing, maximum height, door framing, fire and sound ratings follow the board maker's system and local regulations, and the door frame the door maker's instructions.