In this video, This Old House landscape contractor Roger Cook shows how to construct a wood-timber retaining wall to create a play area.
1. Set up wooden stakes and nylon strings to represent the height and perimeter of the retaining wall.
2. Stretch another level line near ground to represent the top of the first course of landscaping timbers.
3. Dig a 12-inch-deep trench around perimeter of retaining wall.
4. Use a hand tamper to compact the bottom of the trench.
5. Add about 6 inches of ¾-inch stone to trench, then compact the stone with hand tamper.
6. Drill a series of 9/16-inch-diameter holes in the first-course landscaping timbers.
7. Set a timber in the trench and check it for level.
8. Then, stake the timber in place by using a small sledgehammer to drive 4-foot-long rebar spikes through the holes and into the ground.
9. When necessary, use a circular saw to cut a timber to length; use a 3-inch-wide foam brush to apply wood preservative to all freshly cut ends.
10. Measure across the width, from one side timber to the other, to ensure the two are parallel; make adjustments, if necessary.
11. Set the second row of timbers on top of the first course, making sure to stagger end joints by at least 4 feet.
12. Use an impact driver to fasten the second course to the first with landscaping screws.
13. Pour ¾-inch stone behind the wall, then drape the excavated hillside with landscaping filter fabric.
14. Lay a length of 4-inch-diameter perforated pipe on top of the stone, then cover the pipe with more stone.
15. Pull the filter fabric over the stone-covered pipe.
16. After installing the third course of timbers, make a T-shape dead man (tie-back) from two short lengths of landscaping timber.
17. Dig out a T-shape trench into the hillside behind the wall and lay in the dead man.
18. Fasten the dead man to the retaining wall with two landscaping screws.
19. Then stake the dead man to the soil with two rebar stakes. Install one dead man every 6 to 8 feet around the entire wall.
20. Continue building up the retaining wall, using landscaping screws to secure each timber.
21. Cover the ground in front of the retaining wall with 2 to 4 inches of bark mulch.
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