Sagging Floors in Old House


Old 10-20-14, 10:11 AM
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Join Date: Oct 2014
Posts: 2
Sagging Floors in Old House

I'm replacing some very old carpet in an old house (pre-Civil War) with pine wood T&G. Unfortunately, the floors have some considerable sag between the joists. Depending on the joist, it's anywhere from 1/4" to 5/8" from joist to joist. AND, from the center of one wall to the corners of that wall, it has a sag of 1" overall either way over a run of about 6 feet. (This wall is on the house's center beam. The high point is where the beam is pillared - the corners are not pillared.) My joists are on 24" centers (not 16") AND are not regular boards, they're round. Also, the first subfloor is not plywood but 6" wide boards (I think).

My question is, what should I do to fix the sag between joists so that I can lay this wood flooring?

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Old 10-20-14, 10:46 AM
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Join Date: Oct 2004
Location: WI/MN
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Welcome to the forums.

If the joists are fine (not saying they are, this is an assumption), then you need to replace the subflooring with something like 3/4" Advantech.

That said, I would be looking at adding joists to reduce that 24" OC span.
Old 10-22-14, 07:37 AM
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Join Date: Oct 2014
Posts: 2
Thanks, mitch17. What I didn't mention was that there is still a layer of asbestos tile, wood plank underlayment and original heart pine finish flooring on top of the original subfloor. Would putting the 3/4" Advantech over what's existsing (the asbestos tile) work to shape up the sag? (I think this is what's called a "floating" subfloor?) Or do I have to tear up everything to get all the way down to the original subfloor and replace that?
Old 10-22-14, 09:09 AM
Join Date: Oct 2008
Location: New England
Posts: 9,995
Hi dr,
having just done some floor leveling, no easy task, the place I would start would be some level checking in the basement, assuming it is open and you have access. Understanding just where the low spots are and why will help you decide where to start. It would be unfortunate to add a new floor above to compensate for something that can be corrected from below.

Note, before you do ang adjusting from below, let us know as there are concerns related to that process.


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