Timber Retaining Wall Calculator
How many 6×6 or landscape timbers your wood wall needs by course, the deadman tie-backs that anchor it into the bank, the landscape spikes and rebar pins that hold it together, plus drainage gravel and pipe — with a material cost estimate for the lumber-yard order.
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A wood wall is a lumber count, not a block count
Timber retaining walls are the fastest low wall a homeowner can build — stack pressure-treated timbers, pin them together, tie them into the bank, and backfill with gravel. But the material list is nothing like a segmental block wall. Instead of blocks and caps you're buying timbers by the course, plus the deadman tie-backs and fasteners that actually keep the wall standing, and it's easy to under-buy the deadmen and spikes because they don't show once the wall is built. This calculator sizes the whole lumber-yard order — wall timbers, tie-backs, spikes, rebar pins, and the drainage gravel and pipe behind it — so you can price it and buy it in one trip.
How each number is worked out
- Courses: total wall height (exposed height + buried bottom course) ÷ timber height, rounded up. A 6×6 is 5.5 in tall, so a 3.5 ft total wall is 8 courses.
- Wall-course timbers: courses × wall length gives the running length of timber, plus a cut-waste allowance, divided by the timber length and rounded up to whole pieces. Stagger the end joints between courses so the wall doesn't have a continuous vertical seam.
- Deadman tie-backs: a deadman is placed every so many feet along the wall, on every Nth course. Each one uses a tie-back arm buried into the bank plus a short cross cleat at the end; the calculator adds up that timber separately so it isn't forgotten.
- Fasteners: landscape spikes (or timber screws) pin each course to the one below, spaced along the length, with two per deadman. Rebar ground pins are driven through the bottom two courses so the base can't kick out.
- Drainage gravel & pipe: a compacted gravel base under the bottom course, plus a column of free-draining gravel behind the wall and a perforated pipe at the base to carry water away. Gravel is given in cubic yards and tons.
- Material cost: each line is priced at your unit rates and summed. Leave a price blank to drop that item — set the timber price to zero, for example, to price only the hardware and gravel.
This tool estimates a gravity timber wall (stacked timbers held by deadmen). For segmental concrete block walls use the full block takeoff; to price installed vs DIY across materials see the cost calculator; for the drainage detail behind any wall see the drainage calculator. Defaults follow common timber-wall practice, not a specific engineered design — every field is editable.
Timber-wall tips that save a second trip
- Don't skimp on deadmen. They're the difference between a wall that lasts and one that bulges out in a few seasons. If in doubt, tie back more often, not less.
- Stagger the joints. Offset the end joints between courses like brickwork so there's no continuous vertical seam — offcuts from one course start the next.
- Drain it or lose it. Water pressure behind the wall is what pushes timber walls over. Keep the gravel column and pipe even on a short wall.
- Buy ground-contact rated timber. Only PT lumber rated for ground contact (or better) belongs in a wall; anything less rots fast where it's buried.
Frequently asked questions
How many 6x6 do I need for a retaining wall?
Count courses (total height ÷ 5.5 in) then multiply by the timbers per course (wall length ÷ timber length, rounded up) and add cut waste, then add the timbers your deadmen use. A 20 ft, 3 ft wall is about 8 courses and roughly 36 timbers including tie-backs. Enter your wall for its own count.
Do timber retaining walls need deadmen?
Yes, for anything but a very low edge. Deadmen tie the wall into the bank so soil pressure can't tip it forward. A common pattern is one every 4 ft on every second course; taller walls need them more often.
What fasteners hold a timber wall together?
Long landscape spikes or structural timber screws pin the courses together, and rebar driven through the bottom courses pins the base to the ground. This tool estimates both from your wall size and spacing.
Is a timber or block retaining wall cheaper?
Timber is usually cheaper and faster to build for a low wall, but has a shorter life than segmental concrete block. Price both: use this tool for the timber material list and the cost calculator to compare installed prices across materials.