Project guide
How many sleepers for a raised bed, and how much soil?
A sleeper raised bed is a simple box, but the corners, the screws and the soil volume are where lists go wrong. This guide follows the BSW sleeper installation guidance.
The short answer
Lay 100 x 200mm sleepers on their narrow edge (200mm per course) with lapped corners. A 2.4 x 1.2m bed, 2 courses high (400mm), takes 6 sleepers, 24 screws and about 0.7 m³ of soil. Use two 150mm screws at every corner of every course, and the same again to fix each course to the one below.
The formula
- Each side = outside size - 0.1m (lapped corners); 4 pieces per course
- Sleepers = pieces cut from whole 2.4m lengths, reusing offcuts that fit
- Screws = 8 x (2 x courses - 1)
- Soil (m³) = inside length x inside width x (height - 0.1m) x 1.1
Worked example
A 2.4 x 1.2m bed, 2 courses high:
- Pieces: 4 x 2.3m and 4 x 1.1m. The 1.1m pieces pair up in a sleeper, so 6 sleepers
- Screws: 8 x (2 x 2 - 1) = 24 (1 pack of 100)
- Soil: 2.2 x 1.0 x 0.3 x 1.1 = 0.73 m³, so 2 bulk bags of 0.6 m³
- Fabric: about 5 m², so 1 roll
Materials checklist
- Treated sleepers100 x 200mm x 2.4m, pressure-treated for ground contact (UC4).
- Exterior screws150mm long, so at least 50mm goes into the next sleeper. Pre-drill the holes.
- Weed-control fabricLines the base and sides so the soil drains but weeds do not grow up.
- TopsoilTo about 100mm below the top, plus 10% for settling.
You'll also need
- End-grain preservative for every cut end
- A drill and pilot bit: pre-drill every screw hole to stop splitting
- Spirit level and string line to set the first course level
- Optional: gravel in the base on compacted ground, and compost to mix into the topsoil
Step by step
- Mark out and levelClear the ground, mark the box with string and level the area.
- Cut and treatCut the sleepers to length and brush every cut end with end-grain preservative.
- Build the first courseLay the sleepers in a lapped square and screw each corner with two 150mm screws.
- Add coursesStagger the joints like brickwork and drive two screws down through each corner into the course below.
- Line and fillLine with fabric and fill with soil to about 100mm below the top.
Tips from the manufacturers
- BSW says two levels of 100 x 200mm sleepers make a bed about 400mm high.
- Do not make the bed wider than about 1.2m if you can only reach from one side.
- BSW suggests half-filling the box with drainage material such as gravel before the soil goes in.
Mistakes to avoid
- Using old railway sleepers soaked in creosote for a food bed.
- Skipping pilot holes, so the sleeper ends split.
- Lining up the vertical joints from course to course, which weakens the corners.
Frequently asked questions
How many sleepers for a 2.4 x 1.2m raised bed?
One course is 4 pieces: two 2.3m and two 1.1m. Two courses need 6 sleepers because the 1.1m pieces share a sleeper.
How many screws per corner?
BSW: fix the sleepers at each corner with 150mm exterior screws, two per corner being ideal. We use the same again to tie each course to the one below.
How much soil does a raised bed need?
Inside length x inside width x the filled depth, plus about 10% for settling. A 2.4 x 1.2m bed 400mm high needs about 0.7 m³.
Sources
Quantities are estimates for typical jobs, using the coverage figures above. Products vary, so check the data sheet for the product you buy, and talk to a professional for structural, electrical or gas work. SmartBuild is independent and not affiliated with any of the manufacturers listed.
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