Anchoring columns against wind lift?
This is a new construction, nearing completion. I have a (presently) unenclosed 14′ X 24′ terrace which is covered by a (2 1/2 in 12 slope) shingled roof, supported by 8″X8″ fibreglass columns. The floor of the terrace which the columns sit on is a raised Stampcrete deck. My builder says that their normal installation is to have the columns held in place by the weight of the roof only, with no attachments at top and bottom. (He is one of the, if not the, most well-respected builders in my area, meaning if he doesn’t anchor them, likely nobody else does either.)
The house is on Lake Erie’s north shore (“Canada’s south coast”), which is subject to higher than inland winds. Regardless of this fact, I am somewhat surprised, and more than somewhat concerned, that this is routinely done, and evidently doesn’t result in problems. I would be very surprised, based on my little knowledge of construction engineering, if building codes in any locality would allow this.
So my question to you all in the business is what do you do, and is anyone aware of any building codes which would permit such construction? And, does anyone familiar with the Ontario Building Code know if this is allowed, because if code requires it, then I will ask the builder to secure the other columns which support a smaller roof around the other two sides of the house, which are subject to less wind exposure.
Thanks in advance for your expertise. -Brian.
Replies
I don't think I've ever seen a permitted job with unanchored posts. Codes require resistance to wind uplift forces - a gross of 1.2 uplift (minus dead weight) for open structures which in essence means some sort of anchorage is required. There are lateral forces such as wind and earthquake forces that would require some kind of anchorage as well.
Is your job permitted? If it was, the plan checker may have missed this. I would seek the advice of your local building official or a engineer, but I'm sure they would say that post anchorage is required.
The Uniform Building Code requires that columns be anchored. Standard detailing (at least in the US) always has anchor bolts to the foundation for posts. Usually steel connectors are used which also keeps timber members off the concrete to prevent rotting.
The older traditional method is indeed to let the unanchored post be stabilized by the roof loads without concern for wind. many structural columns have printed instructions that have no reference to anything else.
But we've learned to do a lot of things better than they did back when Sampson pulled down the pillars on the Philistines and wrought wreck and ruin. That's why so few Americans are killed in earthquakes, by comparison to the number of lives lost in, say, Turkey.
Mention to your fine old builder that you wouldn't mind if he were to secure the lintles with a screw or two. The down brace of an angled roof with a flat ceiling both framed to a common head are probably offsetting the wind load but the connection detail may have been missed by the plan checker.
I don't know Canadian codes and processes, but I was raised near enough to Lake Erie to know winds there.
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