A well-built retaining wall has many benefits: structures are protected from soil eroding either away from or toward their foundations, the integrity and features of the landscape are preserved, and new outdoor rooms for leisure and recreation are created.
The style, materials and construction you choose for building a retaining wall will depend on the terrain you’re dealing with, but the basic ingredients and considerations stand solid across most types of retaining walls.
Here’s where to begin:
Scale. The higher and broader the retaining wall, the more complex the construction and planning of the retaining wall will be, so consider hiring a pro to help with anything over three feet set in a complicated soil situation. The retaining wall’s cap-to-foundation dimensions will also depend on the climate you live in. Frost is one element that has a real knack for making retaining walls buckle and pop, so if your retaining wall will experience harsh winters, you’ll need to excavate and anchor the retaining wall well past the typical point of underground freezing.
TOM: Building a retaining wall is a great project and you can do it in a couple of different ways. Here to tell us more is This Old House’s Kevin O’Connor and lawn-and-garden expert, Roger Cook.
And Kevin, let’s start by talking about how a retaining wall can help you find a little extra space in that yard.
KEVIN: Retaining walls are an important part of landscaping because they allow you to level out a yard and that provides more usable space. And on a really steep slope, you can use multiple retaining walls. That’s going to create terraces and that’s going to give you a lot of space for plantings.
Roger, you have built a ton of these.
ROGER: I have, Kevin, and there’s two types of walls that the DIY-er can really get into to: one is a timber wall, which is made up of 4×4 or 6×6 pressure-treated timbers; and the other is a concrete block wall.
Now in the timber wall, you’re going to lay your first course in the ground. You’re going to drill a hole and you’re going to bang rerod down in the ground to anchor that first piece in place. The concrete walls are made so that you set the first piece level and every piece gets put right on top of it to build a wall.
KEVIN: And so what about additional support for either of these walls?
ROGER: Well, when a timber wall gets up above two feet tall, you have to put in deadmen. Those are tiebacks. They tie back the wall into the soil to keep it from leaning forward. The concrete blocks are made to go up to four feet. Once you get up to four feet, you have to put in a reinforcing grid behind the wall if you’re going to go any taller.
KEVIN: And we’ve got some good how-to videos about this.
ROGER: We do. We’ve got videos that show you both in every detail on how to build a wall at ThisOldHouse.com.
TOM: So would you guys say if you could handle building blocks as a kid, that you could build a retaining wall?
ROGER: I think the guy who designed them, that’s how he got started.
TOM: (laughs) Roger Cook, Kevin O’Connor, thanks so much for stopping by The Money Pit.
KEVIN: Our pleasure.
LESLIE: Yeah, you know it really is an easy project and, in fact, a terraced yard, it just looks so beautiful. It really is gorgeous to have one in your backyard. And you know, we’re huge fans of making the outside of your house just as beautiful as the inside.
TOM: It’s a very worthwhile project and I tell you, when you need it, you absolutely need it because it’s the only way you’re going to get that usable space in your house.
If you’d like more tips on that project and so many others, head on over to ThisOldHouse.com and check out the great work of our friends Kevin O’Connor and Roger Cook. And This Old House is brought to you by The Home Depot. The Home Depot – more saving, more doing.
Codes. If you’re building a retaining wall project on your own, do some research before you start digging. Local building codes may require permits and other documentation for any structure over a yard tall, and some pretty important utility lines could be running right through your retaining wall project area. So be sure to get your retaining wall plans approved and the utilities literally staked out.
Materials. Several retaining wall material options are available to you and your property, depending on the considerations above.
- Pressure-treated timber: Though not as long-lasting as masonry options, pressure-treated timber provides a rustic, natural look for a retaining wall, and can usually be implemented for do-it-yourself walls up to four feet tall. Timber selected for the retaining wall must be marked for ground contact to prevent soil and water contamination.
- Interlocking concrete blocks: This mortarless solution comes in various sizes and styles, with integrated connectors and a slightly tapered design that enables the creation of curves in the retaining wall’s footprint. Most interlocking concrete block systems also incorporate flat units to cap the surface. Maximum height for interlocking concrete block construction varies, depending on manufacturer specifications and soil conditions.
- Stone, brick or cinder block: For a gorgeous retaining wall, stone, brick or cinder block definitely fall within the province of the pros for guaranteed results in masonry craftsmanship and construction quality. Cinder block requires the addition of textured facing to match up to the natural good looks of stone and the traditional charm of brick.
- Concrete: An experienced pro is also your best bet when it comes to concrete construction. Making a retaining wall is a complex job, and one wrong move can lead to a cracked wall that has to be completely replaced. If concrete is in the retaining wall plan, discuss decorative options for the finish. Many dimensional patterns can be impressed directly into the surface, and veneers such as those from Owens Corning’s Cultured Stone line can be applied for a custom, natural look for your retaining wall.
Reinforcement. Any retaining wall you build should lean into the earth it’s retaining at the rate of one inch for every foot of height. The retaining wall should be further reinforced and stabilized by ties and anchors that reach deep into the earth behind the wall, the style and size of which will vary according to wall materials used. A timber retaining wall over four feet high, for example, calls for 6-foot-long, T-shaped anchors for excellent reinforcement; other systems have anchors integrated into their construction.
Drainage. When building a retaining wall, proper drainage around the retaining wall keeps soil and sediment from clogging up the works and allows water to escape in such a way that the retaining wall’s integrity remains intact. Start by lining the cavity behind the wall with landscape fabric, and replace part of the native soil you’ve removed with gravel. Then lay in a system of perforated PVC pipe, and cover with well-tamped gravel and topsoil. This method will keep your retaining wall properly drained.