Turn a useless and maybe even dangerous slope into a usable garden and play space by shoring up a slope with a timber plank retaining wall. A retaining wall adds value to your property because it increases its usable square footage.
Research local building codes so you don't accidentally violate one and so you know if a permit is required for your project. Codes are available at many local libraries or call your city government's building inspection division, as this office or your city's equivalent is responsible for permitting and inspecting new construction.
Plan the layout of the wall including the deadmen, or T-shaped buttresses that fit in the third tier of the retaining wall. For help with this, visit the Better Homes and Gardens site.
Drill holes large enough for the spikes to fit through every 6 inches along the length of the timbers.
Construct the deadmen. Deadmen need to attach to every third, if not every other, timber of the third tier of timbers. Calculate how many to construct based on the total length of the wall. Affix 3-foot long 2-by-4s in a "T" and attach them to the timbers that are planned for the third tier. Use either nails or construction brackets to create the "T." Attach them to the third tier timbers by toe-nailing them together with nails or with more construction brackets.
Dig the slope and allow room for a backfill of at least 8 inches. Dig "T" cavities into the slope to fit the deadmen.
Create a trench 6 inches deep and wide enough to accommodate the timber, the drain pipe and about a 2- to 3-inch width of gravel. Sit a level on the bottom of the trench and add or remove soil as necessary along its length to make the trench level.
Lay a 2-inch high layer of gravel at the bottom of the trench.
Set the first tier of timber into the trench at a 1/4-inch backward pitch so the timbers are leaning, or are tipped, back into the slope. The timbers need to be level. Drive the spikes through the holes in the timbers and into the ground.
Apply a generous line of construction adhesive along the top of the first tier of timbers to provide some barrier against water seepage.
Set the second tier of timbers. Fit the drilled holes down over the spikes. Dig trenches into the side of the slope behind the wall (the slope you're building your wall to retain) to fit the deadmen.
Put down another generous line of construction adhesive along the top of the second tier timbers.
Set the third tier of timbers, including the timbers with the deadmen attached. Fit the timbers down over the spikes and fit the deadmen into the trenches you dug into the slope for their lengths.
Fix enough perforated drainpipe together to run the length of the wall using construction adhesive. Lay the drainpipe on top of the gravel that sits on the trench floor behind the first tier of timbers.
Place a layer of filter fabric or geo-tech fabric on top of the drainpipe. The fabric needs to be four to five feet wide and the width centered over the drainpipe.
Add more gravel on top of the fabric so that the gravel reaches the second tier of timbers. The width of fabric keeps the gravel from silting, or eroding, over time and keeps particles from clogging the perforations in the drainpipe.
Backfill the rest of the area between the wall and the slope behind it with soil.
Assess the project realistically. If the retaining wall needs to be above 3 feet in height, consider calling a professional structural engineer. The higher the wall gets, the more physics requires professional attention. As the wall's height increases, the force pushing against it from behind increases exponentially. Force is compounded by the upslope of the terrain from the wall and the pressure of wet soil during hard rains. This makes it more difficult to construct a safe do-it-yourself wall. If you need a wall more than 3-feet high, consider terracing the slope into two walls
Tips and warnings
- Assess the project realistically. If the retaining wall needs to be above 3 feet in height, consider calling a professional structural engineer. The higher the wall gets, the more physics requires professional attention. As the wall's height increases, the force pushing against it from behind increases exponentially. Force is compounded by the upslope of the terrain from the wall and the pressure of wet soil during hard rains. This makes it more difficult to construct a safe do-it-yourself wall.
- If you need a wall more than 3-feet high, consider terracing the slope into two walls
Things you need
- Railroad ties or landscaping timbers
- 2-by-4-foot wood planks
- 3-inch perforated, plastic drainpipe
- 12-inch metal spikes
- Filter or geo-tech liner fabric
- Construction adhesive
- Hammer and nails
- Construction brackets (optional)