Introduction
Instead of using stone or timbers, make an attractive, long-lasting retaining wall from pressure-treated 2x4s, plywood and trim boards. Construction is fast and simple, and the materials are much lighter to work with.Overview
Find a buddy
You’ll need to find a guy like my friend Brad to help. He doesn’t need tons of carpentry savvy, just the willingness to work for doughnuts, pizza and beer.
I needed a retaining wall. But I didn’t want to abuse my back by schlepping around landscape blocks. Plus, I didn’t want to bust the bank buying good-looking blocks. So after accessing my internal carpentry database, I came up with a solution: a wood foundation built as a retaining wall. I’ve built dozens of wood foundations (yes, made from treated wood for real basements under new homes), so this was a no-brainer—super easy, attractive and cheap.
This 32-in.-high, 32-ft.-long wall was built in one fairly laid-back day by me, Brad and another friend of mine named Bob Cat (meet him in Photo 7). The materials cost $500, plus another $500 for Bob and his operator, who supplied gravel and some extra topsoil for fill.
Having Bob involved meant there was very little shovel work. And Brad appreciated having Bob there almost as much as I did.
The skeleton of the wall is a treated wood, 2×4 stud wall clad on both sides with 1/2-in. treated plywood. It’s held in place with 2×4 “dead men” assemblies buried in the backfill. The dead men are 2×4 struts bolted to the wall studs and anchored to a perpendicular 2×4 sleeper (see Figure A). The weight of the soil on the dead men anchors the wall against the backfill pressure. It’s important to locate the bottom of the wall below grade a few inches so the earth in front of the wall will anchor the base in place.
Get the right stuff
Ordinary treated wood will last a good long time depending on soil conditions, although wet sites with clay will shorten the wall’s life somewhat. I used ordinary treated wood from the home center, and I figure the wall will last at least 20 years. To build a wall that’ll last forever, use foundation-grade treated wood, the material used for basements. It’s usually Southern yellow pine, a very strong softwood that accepts treatment better than most, and contains a higher concentration of preservatives. You may find it at lumberyards where contractors shop. Or you can special-order it from any home center or lumberyard, although you’ll pay a premium.
Choose nails rated for treated wood: 16d for the framing and 8d for the sheathing. Use 3-in. construction screws for standoffs and dead men connections—again, ones that are rated for treated wood. You’ll also need a box each of 2- and 3-in. deck screws for the trim boards.
Figure A: Wall Anatomy
No matter how large your wall is, it should have these basic elements.
Prepping the site
I had a gentle slope to retain, not a huge hill. This 32-in.-high wall is designed to hold back a gentle slope and is good for walls up to 40 in. For walls 40 to 48 in, place the studs on 12-in. centers and keep the rest of the wall the same. Don’t build the wall more than 48 in. high—a taller wall requires special engineering.
Do the digging with a shovel if you wish. The trick is to dig halfway into the hill and throw the soil on top of the hill. That way you’ll have enough fill left for behind the wall. The downside is that if you hand-dig, you’ll also need to dig channels for the 2×4 struts and sleepers (see Photo 5).
It’s much easier to hire a skid steer (Bob) and his operator to dig into the hill and then cut down a foot or so behind the wall to create a shelf for resting the dead men. Expect to pay a few hundred dollars for skid steer services. The operator can also scoop out the 12-in.-wide by 10-in.-deep trench for the gravel footing, and deliver and dump a 6-in. layer of gravel into the footing. Then you’ll only need to do a bit of raking to level off the trench. A yard of gravel will take care of 50 linear feet of wall. If you have extra gravel, use it for backfill against the back of the wall for drainage. Have Bob and his operator return to fill against the back side of the wall and do some final grading.
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