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Old 09-29-2014, 12:13 PM   #1
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Question about flooring support

We recently moved into a new home that was built in 1926. As best we can tell, the second floor was originally an unfinished attic. At some point, this attic space was converted into living space. We noticed that the floor doesn't feel as solid as we would like. I pulled up some of the carpeting and drilled some holes with a hole saw to investigate.

In two of the three rooms, the subfloor is made of 5/8" plywood, under the plywood there is a gap of about 1/4" (not sure what is supporting the 5/8" plywood, perhaps some supports I can't see yet) to a layer of particle board. The particle board appears to be 5/8". I am certain that this is particle board, not OSB. Drilling through the particle board, I found that the gap between the particle board and the ceiling below is about 5.5", which leads me to believe the joists are 2x6's. The largest span of the floor is about 15 feet. I poked around with a bent coat hanger, and as best I can tell, the joists appear to be about 24" apart.

In the third room, the situation is the same except ( 1 ) the top layer is not plywood, it is particle board (so two layers of particle board), ( 2 ) the largest span is only 12 feet, and (3) the gap between the particle board and the ceiling below is only about 3.5". The ceiling beneath this room is brand new, made of drywall and not lath and plaster like the other rooms. Also, this ceiling just started showing signs of cracks (about 1 month after we moved in).

A few questions. Is this support acceptable for such a floor? If not, what is the correct way to repair this situation, and what are some cost-effective ways ("correct" or not) to repair this situation?

We did have a home inspection done, but because of many other issues around our home, I am beginning to think he did not do a very thorough job.

Thank you for your help!


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Old 09-29-2014, 01:14 PM   #2
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Common issue, people see a big open "wasted" space and figure let make a room out of it.
Big mistake.
Joist are under sized, never should have been 5/8 or particle board.
Joist should have been wider, full span sistered to what was there.
3/4" T & G Advantech is what I would have used with glue onto of the joist.
Inspectors do not have XRAY vision and there not going to be doing any drilling or pulling things apart during there inspection.
Did you hire him without the realtor involved or was it one they picked or suggested?
If it's one they use all the time, guess what, it's going to pass or there not going to get any more jobs from them.


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Old 10-01-2014, 07:26 AM   #3
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Thanks for your reply and input, joecaption. We used a home inspector that was recommended by our realtor. In hindsight, that was a big (and potentially costly) mistake.

We had our situation inspected by a "handyman". His suggestion is similar to what you said: rip out the flooring, sister the 2x6 joists, and lay down tongue-and-grove plywood subflooring. In the room with only 2x4 joists, he recommended doing the same but beefing up the joists instead of just sistering other 2x4's to the existing 2x4's. He said that whole job would cost many thousands of dollars, which will be painful especially since we believe we overpaid for the house to begin with.

Lesson learned: hire your own home inspector!
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Old 10-01-2014, 07:50 AM   #4
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I could be wrong but 2x6 for a 15' span is iffy. Depends on species and such then throw in particle board, plywood, and living space and I believe your way past pushing the limits of any 2x6.

I really don't think sistering the 2x6 will give enough strength either. Probably need up grade to at least 2x10 if not 12. Because this floor is so weak it's flexing and that is what is cracking the drywall.

Believe me when I say this is not my field and there will be others who are much more knowledgeable in this area who will come along.
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Old 10-01-2014, 08:55 AM   #5
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DBL up floor joists will most likely give you proper support.
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Old 10-01-2014, 09:17 AM   #6
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A triangle technique that was successfully used in the past was joist bridging.


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