Advice for subfloor

Old 05-19-14, 03:11 PM
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Advice for subfloor

I am in the process of putting down a new hardwood floor over a space that is approximately 800 square feet. I have already ripped up the old floor (which included about 225 feet of two layers of tile and 3 inches of concrete). I currently have left in place the original plank subfloor, which is over 100 years old.

Considering the age of the subfloor and joists, it seems to be in pretty good condition. The problem that I am facing is that the joists bow in the center. The width of the joists are 25 feet. At the lowest point in the center of the room, it is about an inch and a half lower then the perimeter. I have read various threads and online posts that suggest you can custom cut large shims from 2x10s to place directly on the bowed joists. I know you can also simply attach new 2x10s to the original joists.

Rather than do that, my plan is to simply lay a new plywood subfloor (23/32) over the original plank subfloor. In order to level it, I plan to remove the old subfloor planks around the perimeter (to drop the floor where it is high) and then add 1/2 thick and 1 inch thick strips of wood towards the center (to raise the floor where it is low) and then attach the new plywood sublfoor on top of that. Is that acceptable? If so, any advice on how to do this would be appreciated. I am thinking these strips should be 12 inches apart. Or should I really rip of the old subfloor and work on the joists directly?

Old 05-19-14, 05:39 PM
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Your joists are over spanned. Can you verify a 25 ft unsupported span??? That is an unusually large number.

The proper corrective step is to add a support beam midpoint and jack the center sag out of the floor. What is underneath the subfloor? Basement or crawl space?

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