Trying to figure out how bad of an idea is adding a ~3-4’x6-7’ pergola type ”roof” supported by pressure treated fence posts.

How to understand if it will hold or not? It's in the US PNW, so no severe weather, but strong winds are not uncommon a couple of times a year and, obviously, rain.

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  • Can you sneak in a 3rd post, along with another rafter, in the middle? May 13, 2019 at 1:37
  • Is that rightmost post connected to the fence at right? Are the posts in concrete in the ground?
    – user138719
    May 13, 2019 at 4:34
  • @JimmyFix-it, I don't think there's an easy way to dig a hole for the base there.
    – Nikita R.
    May 13, 2019 at 23:40
  • @user138719, yes, the rightmost post supports both sides of the fence. Almost certain posts are in concrete in the ground.
    – Nikita R.
    May 13, 2019 at 23:41

2 Answers 2


Vernacular architecture - what's the worst that could happen?

Build it and see if it fails.

If it fails, build it again stronger. Seems unlikley to kill anybody or ruin your house if failure happens.

Vernacularly sturdier - don't cantilever it, add two more posts on the open side. Or let it fail, if it's going to, then do that when rebuilding.


4x4 posts are unbelievably strong. They can support thousands of pounds when they’re shorter than 10’ or so. When they get longer than 16’ or so, they tend to buckle under heavy loads.

Your design puts some bending stress on the posts from the diagonal braces, but would not be excessive, even during a storm.

I’d be careful sloping the cover to “drain” over onto your neighbor’s property causing erosion, etc.

Your biggest problem will be getting connectors. I’d start with these type Simpson connectors.

  • "be careful sloping the cover to “drain” over onto your neighbor’s property causing erosion". Yeah, I was thinking about it too. Would probably add a "gutter" and run the drain into either a tank to collect water or into the actual drain, it's pretty close to there.
    – Nikita R.
    May 13, 2019 at 23:51
  • "Your biggest problem will be getting connectors". Sorry, to clarify, which part of the so-called "design" you were thinking would require these (or any other) connectors? Asking because of inexperience, not trying to argue.
    – Nikita R.
    May 13, 2019 at 23:52
  • 1
    @NikitaG. I’d use one connector where each board meets another. Relying on nailing is not reliable, especially when the boards want to pull apart.
    – Lee Sam
    May 14, 2019 at 1:11

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