How long would you expect a timber retaining wall to last?

Question

Thinking about buying a house on a very sloping block of land.

Obviously I am not a builder or landscaper, but to my eyes the timber posts in the retaining walls look old, and mis-shapen in parts. The current owner says walls are 8 years old, that you'd expect the walls to last 20 years.

Any comments? Anything obvious that would give me a clue?

Basically, if a timber post is buckled is that a sure sign the wall is no good, or is it not that simple?
Should I just forget about this house, I don't want the expense of rebuilding retaining walls any time soon!

Answer 1

A timber retaining wall can last a very long time if done correctly. Railroads have used them for ages. They have to be treated wood. If the walls been up for eight years, dig up some dirt on the high side and see how the timber looks. If it's wet and spongy, that's a problem. If its wet and hard, you're fine.

The buckling is a bad sign. That means the wall wasn't built properly in the first place. The buckling can continue until the whole wall snaps. You'll need an engineer to confirm, but common sense tells you its a problem.

Answer 2

I am an architect. Regardless of your lack of qualifications, if they look old and mis-shapen, or if you see signs of earth movement, that is a sign of a problem. There is no way in this forum for me to evaluate the actual situation, of course, and particularly just how long a timber retaining wall "should" last, but please get an independent evaluation of this situation. Depending on the location, any retaining wall over a minimum height, such as four feet in many locales, needs to be engineered.

Here a couple of things you could do:

1. Call the local building department and find out the rule that applies in the location of this property. If the walls require engineering, did the seller have them built with engineered plans and under permit?

2. The building department can also tell you where to call to see if there have been any recorded land slides in the area.

3. If you are very serious about the purchase, spend a couple of hundred dollars on a structural engineer to inspect this wall and give you a report. That way you will have the peace of mind of knowing it's ok, or you will know about how long you can expect it to hold and adjust your offer based on this information. (Are you getting a building inspection?)

Answer 3

Did you have the house inspected? The inspector should have taken a look at the outside too.