Ask a Landscaper: How do we install patio columns?

Columnsarbor_2Question: We are preparing to install a cover on our courtyard and want to use fiberglass columns as the corner braces. Do we need to attach these to our pavers (and how?) or will the weight of the attached cover be sufficient?

Answer: From Pamela Berstler of Flower to the People:

For this answer, I will assume we're talking about some kind of solid patio cover, like a pergola, not just a fabric awning, and that the columns are hollow decorative columns.

First, let's have a quick physics review: A little something we call "shear" will bring this project to grief in very short order if you don't consider how the cover is to be "held up" (as opposed to what I think is your assumption that it will "bear down" on posts).

The essential elements of your design are these: How big a span across do you want for the cover? And how many posts firmly sunk into the ground (not just attached to pavers) do you need to carry the weight of the cover? Corner braces may not be enough. Usually you need a post every 8 feet or so, unless the cover is engineered to span greater areas (with aluminum or steel beams).

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(Photo: Mr. Deck)

Also, unless the cover is completely attached and cantilevering off an existing structure that totally supports the weight of the cover on its own, the posts holding up the cover have to be sunk into the ground and into concrete footings (18 inches to 24 inches deep or so if the post height is 8 feet or taller).

Think about it, pavers are just sitting on top of the soil (even if they’re on top of a 4-inch concrete slab), so they’re not providing any support. You lean against the vertical thing you attach to them and that vertical thing (like your columns) moves. The vertical posts, columns, or whatever have to be in the ground to provide support for the cover attached to the top. Similarly, if wind hits the cover, pressing it, and moving it around, the result is pressure and movement on the posts. No support for the posts, posts and cover falls down.

Usually these fiberglass columns have either (a) metal brackets that attach to a support sturdily installed in a concrete footing, or (b) are just cladding that fit around a wood or metal post sturdily installed in a concrete footing.

So, in order to get an overhead cover that will last the ages, it’s best to start digging!