"Levelling" a wooden subfloor

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Old 04-11-11, 07:38 PM
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"Levelling" a wooden subfloor

I'm about to prep the subfloor in one of our bedrooms for a pre-finished bamboo flooring installation. The subfloor is flat but not level (dips downward) on one side (70% of the area) and then levels out where the last section of plywood starts. I've decided to try to fix the smaller area where the floor is level but effectively dips down in relation to the slope of that 70% of floor.
What's the best way to build up the smaller area so it becomes even with the rest? It's about a 3'x10' area that "drops" a full inch and a quarter over the 3-foot distance from the joint to the wall. I am going to install another layer of 1/2" plywood over the existing 3/4 inch subfloor so that the 2" cleats that I will be using on the 5/8" bamboo flooring won't penetrate the subfloor.

Thanks!
 
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Old 04-11-11, 09:27 PM
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Why is the floor dipping so much? Although the following might sound like a lot of work, it is actually the best way(for such a large area) and it shouldn't take more than 2 hours. Cut out the subfloor section and sister some 2 X 6's to the floor joists and level as needed. You might even be able to put the original piece of subfloor back. The floor will now be flat and you wont have to worry about shimming pieces all over the place.

The only problem would be if construction adhesive was used to attach the subfloor when it was built, in which case you will need 2 specialized tools. A strong friend and a case of beer.
 
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Old 04-11-11, 10:23 PM
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Thanks. What you had suggested was the original plan but I abandoned it because I didn't want to damage the drywall that's hung on top of the edges. I might have to just cut the subfloor as close to the walls as possible and sister some wood to the joists.

The house is 70 years old and built on alluvial deposits. I've noticed some redundant foundation work and that redwood stumps were actually used as foundation! Oh yeah, It's survived at least one major earthquake in the San Andreas Rift Zone. Rooms on the periphery of the house all have floors dipping (partly or entirely) towards the exterior walls. Few corners remain square and essentially nothing is still level. Not sure if that's how they made them back then in these back woods
 
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Old 04-12-11, 03:52 AM
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You can cut right up flush to the wall with a Toe Kick saw. Home Depot rents them or you could buy a cheap one at Northern tool.
Those stumps under that house make a great ladder for termites to get right to the floor joist.
When's the last time you had an exterminator come look and see if you need a treatment? It's free and it just might save your whole house.
I just hate it when I go under a house and see all forms of bracing, sistered floor joist, stacks of red bricks just sitting on the bare ground trying to support a floor.
If the whole floor is sagging in the middle then pore at least three new 24 X 24" X 6" thick concrete footings with rebar in the middle of them and install new piers and a doubled up 2 X 8 to and jack the beam up until the floors level to act as a center beam in the middle of the span. It will take out the sag and stop the floor bounce.
 
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Old 04-12-11, 03:19 PM
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I like joecaption idea. I know you hadn't planned on doing the supports, but it would only take a few hours to dig the holes, and yes you might end up doing some sheetrock repair as well.(man it seems that this might be turning into a bad movie that I've seen before) I don't know how good Redwood is against termites. Around here all the old houses were on Locust posts and I haven't seen may rotten ones or termites.

Also, if this house is on clay, I would hate to wake up 2 years later and find that it has moved again.
 
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