Build a Solid Retaining Wall: Phase 1 First of Two Parts

By Mark Clement Welcome to this two-part series about designing and installing a unique and attractive retaining wall. Even though this is an outdoor project, it requires a carpenter's skills, tools and mental faculties for design, layout and installation. Ues, basic retaining walls are usually the landscaper's domain. Typically, if a yard structure is required, he stacks 6-by on edge to create a monolithic vertical surface in the customer's yard. However, remodeling and new-construction applications often need a wall, either to cut out and hold back a hill for a new deck addition, pool, or garage or to expand the front yard in urban settings. Time and again, customers with an eye for style and substance want something with cachet, shadow lines — and whatever their neighbor doesn't have. This wall has it all. Skill set and design As I said, it takes a carpenter's skills and tools to build this wall. Vertical and horizontal lines create the shape, shadows and staying power that please customers. The reason it takes skill to build this wall is that it's an unconventional design — one I ripped off from my days in marine construction. Seawalls along the coast where I used to build are tough. Unlike the landscape-timber wall based on a massive membrane of solid wood, a seawall's tenacity comes from posts (pressure-treated pilings) driven deep into the beach sand. The posts are then backed with 3x10 T&G planks. The system is big, heavy and can take the punishment of the "perfect storms" that batter coastlines every year. (In fact, it was because of the perfect storm made famous in the book that I was doing this work in the first place.) The other thing that's good about this wall system is that it looks good — and it looks good for a long, long time. While a heap of timbers eventually and almost inevitably starts tipping or bulging at some point, posts driven into the earth are pretty much there to stay. What's also nice is that in a landscape application, you typically don't need the brawn of full-on seawall pilings and 3-by. All this wall needs is 6x6, 2x10, smartly designed returns and a bunch of concrete. Excavation and layout While it's possible to hand-dig the post holes for this wall, why would you? Rent a skid-steer (or similar machine) with an auger and bucket attachments. You'll make the money that you spend on it back PDQ. Before digging, call the local Dig Safe phone number and have all utilities marked. Give them at least five days to mark the lines. They usually say they can be there in three, but that's often wishful thinking. Getting stymied by a gas or water line or a cable isn't worth your time. And breaking one is worth even less of your time. Excavate the hill at least 3 feet from the location for the wall. Site prep. I like to do my site prep before laying out the wall location. First, if I have to, I excavate the hill no less than 3 feet from the back edge of the wall location. If it's possible and safe, loading the fill onto the top of the hill makes life easier later. It's not always possible with a bucket-type machine, so make sure to include the time for moving soil around into your bid. Another excavation option is a mini-excavator. It didn't work on my project due to space constraints and site conditions, but its long arm can dig the post holes and trench required. And its reach can often place dirt on top of the hill better than bucket machines. Whatever you use, make to sure to include the cost of storing and/or moving the earth you excavate to its final location. On this wall, we actually had to trailer the dirt around the house and load it from behind (ugh). Once you've notched out the hill and moved the dirt, you're ready to lay out post height and location. Marking holes. I got lucky on this wall; it was situated against a sidewalk, and I could mark post locations on the concrete. However, string lines and 40-penny nails work well to establish the front edge of the wall, say in a backyard location, and give solid positions from which to pull a tape for the 3-foot centers the posts sit on. For marking post-hole locations, I rip a little piece of yellow caution tape off the roll and set it into the center of the hole location with a 12d nail. This marks them until I can dig. If the wall has return legs, I lay their post holes out at this time, too. An auger makes quick work of digging post holes. It may be necessary to remove obstacles preventing proper location of a post hole. Digging holes. The next step is to drop the holes. Using the machine's hydraulic auger enables you to sink wide, plumb 4-foot-deep shafts right on the mark. Clean the edges of the holes so there's a flat top of hard dirt. Sometimes rock, roots and other obstructions snag the auger and you have to bust them out, which means having a 14-pound combination hammer around will just might save the day. Slap a spade bit or bull-point chisel in there and knock off the side of a rock or hunk of concrete to sink holes straight. Measure each post individually to ensure a straight top line. Determining post height. While it makes sense in some applications to follow the slope of the ground, I usually want a level wall cap, so I use a laser level to shoot grade and get the post heights exactly where I want them. I haven't dug any holes yet, so I record the heights and locations of my far left and right posts above the ground, which I'll use in the next phase: setting posts, planking the wall, back filling and finishing. To read about those next steps, click here. Mark Clement is a remodeler and author of The Carpenter’s Notebook and The Kid’s Carpenter’s Workbook, Fun Family Projects! Find out more at www.TheCarpentersNotebook.com. RELATED ARTICLES: Build a Solid Retaining Wall: Phase 2