OT Deck Footing Location Mis-measurement Causes Off-Center Placement

D107 · September 13

For small 8x8 back deck replacement—which never had footings before—now designed according to code. (3) 15"W footings were poured. For at least the first one, Instead of the center being 92.5" it is 95", 2.5" too long. So if we keep the deck dimensions the same as the plan and leave the footing as is, the 4" wide Pressure Treated Vertical Support would now run from 90.5" to 94.5", a little off-center. The plan is for the footing to be covered by bluestone

The question is how crucial is the load not being perfectly centered? The new deck is about two feet longer (8'x8') than the old one which had no footing ever, only 4x4 PT wood. This is the carpenter's mistake, but rather than demolish and re-pour the entire footing, perhaps just enlarging the deck 2.5" is the solution? Or just ignore the issue?

But I also can't yet verify the accuracy of the location of the two other footings or the pad at the bottom of the stairs. (Note the drawing shows a 3.5" difference between the full deck length (8ft) and the proper center of the footing but since the center is actually now 95", the difference is 2.5" not 3.5". The footing in question is the solitary on the right side of drawing.) I discovered this fairly recently by just deciding to measure myself, and now this monkey wrench into the job at the worst time.

mattmia2 · September 13

I don't think there's any reason you can't put the post 2.5" off center on the footing.

mattmia2 · September 13

are you sure you're measuring right? are you sure that isn't allowing for rim joists and trim and such?

D107 · September 13

@mattmia2 I'm not sure what I'm not accounting for but I know the overall measurement should be 8' x 8' since we're kind of cramped for space there. But even a few inches shouldn't alter the overall issue. If your first reply holds, then that's good news. But since there doesn't seem to be any justification for the initial mismeasurement then it makes me wonder if the carelessness is habitual, which is a red flag. Also I'll now have to verify the locations of the pad and other two footings.

mattmia2 · September 13

is the footing 2.5" too close to the center or too far from the center? there may be a .75" or 1.5" finished skirt board around the outside of the deck that covers the rough framing that makes the rough framing shorter than the finished dimension of the deck.

mattmia2 · September 13

I didn't see the dimensions between the posts called out on the drawing until just now. i'd ask about it but there certainly is some tolerance when you're setting forms and pouring concrete that if you fix when you start the framing won't be a problem. 2.5" seems like a bit more than i'd like but things can happen and it can be fixed when the posts are set.

D107 · September 13

The distance you're seeing measured of the current center is 95" east of the brick wall to the left of the tape measure, so since center should be 92.5" east of that brick wall, it is now 2.5" too far east of center.

mattmia2 · September 13

might be that the existing walls aren't square and depend on where you measure. they may have fuond a dimension that was the average of square to each wall if the angle is a few degrees greater than 90 or if they just plain aren't straight or it may be perpendicular to the wall on the left and the other posts.

D107 · September 13

I don't think the wall could be out of square enough over such a short distance to account for the 2.5" mistake. My guess is that the carpenter conflated the known overall deck dimension of 8ft with the actual center measurement to the center of the footing—easy to do in the drawing if you're not paying strict attention. Anyway, sounds like it's not an emergency. Thanks as always.

Jamie Hall · September 13

So long as the entire post rests on the footing, you should be alright. But the post mustn't overhang the concrete.

OT Deck Footing Location Mis-measurement Causes Off-Center Placement

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