Building retaining walls is more that just pouring a pile of concrete—-or stacking a bunch of stones together and hoping for the best. Retaining walls are “systems” that require proper footings, proper construction, proper drainage and proper back-fill—-depending on the types of walls, height etc. Many homes have retaining walls installed along the driveways so that access is possible to the garage or basement. These walls are often poorly constructed, usually have inadequate drainage systems, and have no barriers to prevent falls—-especially in older homes.
Of all the components of the retaining wall (putting personal safety aside for a moment), its drainage system is perhaps the most important. You can build walls like the this brick retaining wall and if it is drained properly it will do its job. But, if you build a nice concrete wall and backfill it with non-draining fill, the result will be leaning and possible collapse of the wall—-sooner or later. Here are a couple of pictures of poorly drained retaining walls that are nearing the point of collapse.
As a general rule, if you run an imaginary plum line down from the top of the wall, and the distance from that line to the base of wall is greater than ½ the thickness of the wall—-collapse is possible due to gravity—-regardless of pressures against it. (As a side note—-concrete is heavy, and tipping over concrete is not a good idea.)
Loose stone walls can sometimes be more forgiving because water that gets behind the wall can drain out though the many openings. Solid concrete and brick walls need weep holes along the base of the wall to relieve hydrostatic pressure. All types of retaining walls should have drainable fill behind them so that hydrostatic pressure is not an issue.
Some loose stone walls employ TROLLS to keep an eye on things.
Charles Buell, Seattle Home Inspector
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Chuck , You always come up with the best articles that are both insightful and entertaining to read. Thanks for posting this blog about retaining walls and the danger they pose.
Thanks Sonny—my pleasure
Not a very good retaining wall if it’s not retaining 🙂
Dan it would appear that you have broken through the retaining wall 🙂
good one, keep it up!
charles i had a stone retaining wall collapse on my property the wall was 50 years old or better my insurance company will not cover the damages for these reasons article 14 this peril covers buildings and personal property against the collapse if they are damaged or destroyed when part or all of your dwelling building or outbuilding experiences a direct structural collapse that is caused by weight of ice snow or sleet it does not include collaspe that is caused by settling expansion contraction movin bulging buckling cracking or deterioration defect mechanical breakdown wet or dry rot nor does it include collapse by flood or surface water if its possible can you give me any ideas on how too win my appeal isay its a act of nature and it should be covered thank you for your help
Tony, I have no idea how to help you with this question. I would consult with a company that builds these walls and see if they can be of any help. When it comes to insurance companies—who can tell. Maybe consult with another insurance company to see what they would do. Have you talked to a lawyer that specializes in insurance issues?
Yeah, unfortunately Insurance companies typically only cover things that have a direct impact on the value and condition of the structure or “real property”. Though I have seen insurance companies cover fences and other accessory improvements. Go figure?
Thanks for this amazing article Charles. The facts presented in the article are well explained in the pictures. The need for a good drainage system in a retaining wall cannot be over estimated.
That first picture is *exactly* my situation; 1928 house in Seattle, the wall (a left side, too!) cracked away from the foundation, leaning inward. Sigh. There isn’t much hope is there? Do you have a preference of replacing it with another poured wall or the newer retaining wall blocks available? It’s about 5 feet high.
Bob, there are lots of walls in Seattle that look like this one 🙂 Anyway—either type of retaining wall can work just fine—it is all about doing the backfill and drainage properly. As is evidence by all of the failing walls around there were a lot of installers that didn’t understand about drainage and backfill.
My house in Wallingford was built in 1926. My driveway looks like the one in your picture except it slopes down to the street. I’m ready to replace the wall(s) but I would like to widen the driveway at the same time if possible. I have tried searching the city code and can’t find an answer. Right now the wall is about 5 or 6 feet from the property line. Do you know how close to the property line the wall can be? Also, I’m sure this driveway was just carved out of the hill and has zero backfill. There is a rockery at the end of the driveway on both sides. How much backfill is enough?
Jill, I recommend a call to the Department of Land Use—they will for sure have the answer. That said, I suspect that the retaining wall could be on the property line depending on what kind of wall it is. Buildings on adjacent properties will have to be taken into consideration as well so that their foundations are not compromised. Let us know what you find out.
Yes! You said it, retaining walls aren’t just random structures that can be casually stacked up. Draining systems, proper placement, and other things come into play. Thanks for sharing!
Oof, didn’t realize the image would be so large for my Retaining Walls Dallas logo, I thought it was going to be my profile image, my bad.