Form the fabric into a large C shape, with the open mouth of the C facing downhill. Timber walls should be built on a trench filled with about 6 to 8 inches of compacted gravel so that the top of the first timber is even with the grade of the soil.īefore adding gravel, lay down enough landscape fabric to contain the new gravel. A good retaining wall begins with landscape fabric, gravel backfill, and 4-inch perforated drainpipe. You may be able to have the design cost included in the price if you get several bids.Īs stated before, retaining wall failures are primarily due to poor drainage. Expect to pay an additional 10 percent if you hire a landscape architect or engineer. Preparing the site may raise costs substantially if it contains clay soil, heavy rock, or a natural spring. If you need a taller wall, consider step-terracing the slope and use two walls that are half as tall.įor a timber retaining wall you can expect to pay between $10 and $15 per square foot, calculated by the area of the wall face a 4’ x 15’ wall would be 60 square feet or between $600 and $900. This is why walls over 4 feet high need to be engineered and may not be suitable for a do it yourself project. An 8-foot high wall would need to hold back as much as 160 tons. A 4-foot-high, 15-foot-long wall could be holding back as much as 20 tons of saturated soil. Small retaining walls have to withstand enormous loads. Most often this is due to poor drainage or improperly securing the timber retaining wall to the slope. Of these, there may be a few that were improperly installed and show signs of bulging or leaning. If you look around your neighborhood you may see several properties with existing timber retaining walls. Simple garden retaining walls may not require any inspections or plans, but larger retaining walls or retaining walls located near easements or property lines will often require a site plan be submitted with specifications on the timber wall construction and costs. You should consult with your local building inspector and zoning department to see what permits are required. You may want to consider hiring an engineer to design and certify your retaining wall if it is going to be higher than 4 feet. If your property needs a retaining wall, or if the one you have is falling apart you may be able to build a timber retaining wall yourself. These structures can also increase usable yard space by terracing sloped properties.Īlong with sloped landscapes where water runoff causes hillside erosion, ideal locations for a retaining wall include spots downhill from soil fault lines and where the downhill side of a foundation is losing supporting soil or its uphill side is under pressure from sliding soil. They are used to hold back soil on steep grades, provide level access to homes or walkways, or are used for landscaping and gardening functions. Timber retaining walls have been used installed in residential landscapes for generations. To finish the project, we round the corners with a simple 45-degree cut (Image 4).Retaining walls can be constructed from stacked field stone, block, concrete, or timber. Then, remove the ends of the boards, leaving a 3-inch overhang. Attach the top plank using 3-inch wood screws driven every 12 inches. If you need more than one plank to cover the length of the wall, cut them on a 22-degree angle to fit them together. Center the 2x12 cap on the top timber, allowing a 3-inch overhang on both sides. We're using 2x12 planks cut at 45-degree angles and fitted together in a point. Once you have all the timbers in place (and backfilled), add a top cap. Because the grade of this yard has a slight slope that will promote water runoff, we can skip this step on this project, but we will add gravel for drainage and back fill with dirt. Most retaining walls require drainage and are built with a perforated pipe set behind the wall in a gravel base. Repeat the process, building subsequent rows and offsetting the timbers so that the ends of every row are in alignment (Image 3). Use a hand saw to cut off any excess in order to make the ends of the wall even (Image 2). Again, attach each row to the row below it using 60d spikes (Image 1). Build the next row, remembering to stagger the timbers. Secure this second row to the foundation row with 60d spikes, using the pre-drilled holes. Pre-drill holes for the spikes about every 8 inches. Offset the joints as you install the second row.
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