Pressure treated retaining wall

I'm in the early stages of planning for a small implement shed, 16X32, to be built adjacent to my barn. There is a 42" change in elevation between the barn and the front wall of the implement shed. I'm debating building a block wall at the back of the shed or using pressure treated lumber. Pressure treated will be a lot quicker and cheaper so its my first choice if it will be durable enough to last ~20 years.

Has anyone used pressure treated for this type of wall? How well did it work. I see a fair number of pressure treated retaining walls, but they're all relatively new so I'm not sure how well they hold up.

10 years ago I used pressure treated 6x6(lined with heavy plastic before I backfilled) as a retaining wall. So far not much other than a little moss. The timbers are in excellent shape. At the time I thought the plastic would help keep some of the moisture away from the wood.

Its just one opinion but it seems to have worked for me.

pt should be fine. You could also look into used railroad ties. Are you planning on putting in some deadmans? 42inches is getting to the point where the wall could start leaning without them. A good overkill way to do it would be to backfill about 4 inches with gravel and leave drain holes at the bottom. That way the wood won't even hardly be exposed to moisture since it will all drain through. (This kind of depends on whats above the wall, ie if you're going to get a lot of run off or not)

Check out the project on TractorByNet.com called "I feel like Spencer Jr." PT retaining wall

The slope looks similar to what you described.

>> Check out the project on TractorByNet.com called "I feel like Spencer Jr." PT retaining wall


Thanks a lot for the link. This is real similar to what I was planning. I'd been thinking of 2Xs for the back wall, but if plywood works, I may use that.

A vertical timber retaining wall, 42 inches tall, is too tall to stand reliably, unless it is tied back into the slope. Genarally, a wall needs to be about 2/3 as thick as it is tall, to withstand the earth pressure.

You can do this with cribbing, by running headers back into the slope and using the earth mass to support itself. I suppose you could do the same thing with plastic geogrid, like they do with the segmental concrete walls, but I doubt you'd save anything over the cost of timber cribbing.

<font color="blue"> A vertical timber retaining wall, 42 inches tall, is too tall to stand reliably, unless it is tied back into the slope. </font color>

Can't you accomplish the same thing by sinking the posts deep enough into undisturbed ground? I've got a PT wall that is about 36" made of 4x4 posts sunk about 3' into the ground backed by 2x boards that has been doing pretty well for a couple of years now.

It is just a landscaping feature, so if it ever fails I'm not in real trouble (would build a block wall if I had to), but seems to work OK...

</font><blockquote><font class="small">In reply to:</font><hr />
Can't you accomplish the same thing by sinking the posts deep enough into undisturbed ground?

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Yes, you can. If you have a post hole auger that will go deep enough, you can cantilever the wall. Without dooing any calculations or knowing much about your soil, I'd think that 4 foot bury would be fine. Since that's still in the range of 8 foot poles, it sounds like a reasonable solution.

<font color="blue"> you can cantilever the wall </font color>

That is exactly what we did. The posts are sunk to a depth equal to or exceeding the height of the wall. We set the posts back at about a 5 degree angle. Seems to work OK so far.