Garden

9 Step Timber Sleeper Steps Build with Oak Sleepers Over a 5-Metre Slope

February 03, 2026 by Garden Content Team · 7 min read

A 5-metre slope with about 1.4 metres of fall works out at nine risers of roughly 155mm. Oak sleepers at 200mm by 100mm can carry the flight if the MOT Type 1 base, rebar pins, and 50mm land drain are set before the back-fill goes in.

Rise, going, and sleeper size before digging

Measure the vertical fall before lifting a spade. A 5-metre horizontal run with a 1.4-metre drop gives a gradient close to 28 percent, and dividing the 1400mm fall by a comfortable 155mm riser gives nine steps. UK Building Regulations Approved Document K caps a private stair riser at 220mm and sets a minimum going of 220mm, so 155mm risers with 280mm goings sit comfortably inside those limits.

Oak sleepers at 200mm by 100mm create an awkward choice. Laid flat, two courses give 200mm and one course gives 100mm, so each 155mm riser would use one and a half sleepers with waste built into the cut list. Turn the sleeper onto its 200mm face and the riser becomes a single piece, though 200mm is too tall for nine steps over this fall. The workable version is a 155mm riser ripped from a sleeper, or a riser made from a 150mm sleeper section if the yard stocks the smaller 250mm by 150mm profile. Check the actual sleeper dimensions at the timber yard before fixing the step count, because nominal and sawn sizes can differ by 5mm to 10mm.

Pegs, line, and the slope that changes shape

Drive a tall peg at the top of the run and a short peg at the bottom. Stretch a builder’s line between them and hang a line level from it, then treat that line as the finished gradient. Mark each tread position along the line at 280mm horizontal intervals and transfer those marks to the ground with a plumb bob.

This is where an even-looking bank starts to show its humps. A 5-metre run rarely falls at a steady rate from top to bottom. Where the ground bellies out, the excavation deepens; where it dips, the level comes up with compacted hardcore.

Use a 1.2-metre spirit level on a straightedge to check each tread platform from front to back before the timber is fixed. The front edge of every tread should sit 5mm to 8mm lower than the back edge, giving rainwater a forward fall before it can collect against the riser. Self-builders often miss that small fall, and oak treads can cup and rot at the back edge within three winters when water sits there.

The oak you have to lift

Green oak sleepers weigh 60kg to 80kg each at 200 by 100 by 2400mm, and they move as they dry. Reclaimed oak is cheaper, although it often comes with old bolt holes, creosote, and embedded grit that can blunt a saw chain in two cuts. New green oak from a sawmill costs more per piece, cuts cleanly, and tans to silver-grey over 18 to 24 months without treatment; tannin bleed can stain pale paving below the run for the first year, so keep a porous gravel margin at the foot of the steps to take the run-off.

Excavation, Type 1, and the water path

Dig each tread bay back into the slope until you reach firm subsoil. The cut face becomes the seat for the next riser up the bank. Aim for a level bench at each step, over-excavated by 100mm to 150mm to receive a compacted sub-base of MOT Type 1 crushed stone.

Lay 100mm of Type 1, then compact it with a plate compactor or a hand tamper in two passes. On clay, treat compaction as part of the structure. Oak is heavy and unforgiving, and a riser bedded on loose spoil will tip forward the first time the clay swells after rain.

On free-draining sandy ground, the Type 1 layer can reduce to 75mm. Keep the layer continuous from step to step so water moving downhill through the soil has a drainage path along the flight.

Run a 50mm perforated land drain behind the top riser if the slope sheds a lot of surface water. Wrap the pipe in geotextile, bed it in 20mm clean gravel, and lead it to a soakaway or to a ditch at the side. Standing water behind oak can lift a whole flight over a decade, and the land drain is cheap insurance against that movement.

Back-fill behind each riser with 20mm clean gravel. Soil holds moisture against the end grain; gravel lets water drop through the structure and away. This back-fill detail, together with the front-to-back tread fall, accounts for much of the difference between flights that survive and flights that fail.

Fixing the risers with rebar and screws

Each riser sleeper gets pinned to the ground with steel reinforcing bar. Drill two 16mm holes through the sleeper near each end, then drive 600mm lengths of 16mm rebar through the timber and 400mm into the subsoil with a club hammer or an SDS breaker. Two pins per riser hold a single course.

Where two courses stack to make the full riser height, screw the upper course to the lower course with 200mm TimberLok or landscape screws at 400mm centres. Pre-drill oak with a 6mm bit, because the grain splits when long screws are driven cold.

Butt the next tread sleeper against the back of the riser and screw down through the tread into the riser below with the same landscape screws, using two screws per joint. The tread becomes the bearing for the riser above it, so each step locks into the one beneath. Check the riser face with a level before pinning it plumb; once the rebar is driven in, adjustment means pulling the whole pin.

A worked count for a 900mm-wide flight

Nine steps at 280mm going each consume 2520mm of horizontal run. That leaves roughly 2480mm taken up by riser thickness and by the top and bottom landings across the 5-metre measured slope length. Each step uses one riser sleeper at 2400mm wide cut down to the chosen path width, plus tread sleepers to match.

For a 900mm path width, one 2400mm sleeper cuts into two 900mm tread pieces with offcut left over. For a 1200mm flight, two cut lengths can be butted together across the width.

For nine risers and nine treads at 900mm width, allow around eighteen sleeper lengths once cutting waste is included. Call it twenty sleepers to cover the two ripped riser pieces and breakage. At green oak prices of roughly 35 to 55 pounds per 2400mm sleeper, the timber alone runs 700 to 1100 pounds.

Add a bulk bag of Type 1 at around 50 pounds, two bags of 20mm gravel, a 6-metre coil of land drain, and a box of 200mm landscape screws near 40 pounds. The rebar list is eighteen pins at 600mm lengths, from a single 6-metre bar cut down.

Setting the treads and finishing the surface

Work from the bottom up so each completed step gives you a platform for the next. Bed each tread on its compacted bay, screw it to the riser behind, then set the next riser on the back of that tread. Re-check the front-to-back fall on every tread as the flight rises, because errors compound and a 5mm tilt repeated nine times leaves the top step visibly wrong.

Dress the tread surface with a wire brush to lift the grain for grip, or rout a pair of shallow grooves across the leading edge. Oak is slick when wet, and the silvering process makes it slicker before it weathers rough. A 50mm gravel margin on both sides of the flight catches tannin run-off and keeps soil from washing over the tread edges in heavy rain. Nine steps set true and drained can outlast the fence beside them.