Comments for Small Fence on Retaining Wall

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Mar 30, 2010
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Fence Posts on a Retaining Wall
by: Editor - Rich Bergman

Yes it can be used but because it is 60" (5 feet) high there are a few precautions you should consider. We have just completed a new round of testing with Intertek engineering. They tested the 6x6 and 4x4 anchors on single unsupported 42" high pressure treated pine posts.

They tested three samples each to failure. Failure was defined as when the wood post started to show signs of cracking of splitting or when the anchor base began to bend and reach maximum holding power.

The 42" post with the 4x4 anchor was tested with three samples. Test results were 400 lbs, 300 lbs and 300 lbs for an average load to failure of 336 lbs.

If you use a post that is 18" longer you will certainly have more leverage and the force exerted on the anchor will be greater. I can't tell you exactly what those numbers would be because we would have to test them.

But we also have a post brace that is designed to assist in these kinds of applications. We hired Intertek to test the same height and size post with one - the only difference was the additional post brace. The results were an average load to failure of 500 lbs.

Now, at five feet the results will not be 336 lbs or 500 lbs. Also, over a straight run of railing or fence in your case of 25 feet long will require closer post spacing and maybe even the odd post brace. But keep in mind this being a fence and depending on a number of other factors it may not be subject to any load requirements. BUT you must check locally to verify that yourself.

Here is a little calculation sample to help you out. Over 25 feet you will need 6 posts. If you only use the post anchors and no braces the total load capacity for a 42" height would be (6x336=2016 lbs). If you use a post brace at the two end posts you would get (2x500 + 4x336 =2344 lbs).

If you used all posts with braces you would have (6x500=3000 lbs). Now keep in mind this is for a 42" high post because I only have engineering for that. So you would have to speak to someone to see that the strength reduction would be if you go to 5 feet high and whether that will work for you. You could also have 6 sections 4 feet long and then you end up using 7 posts and get the extra load from that post.

Also and very important, the post base and brace will require a width of 8.5" to fit on top of the retaining wall.

I hope this helps you out.

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