Floor ain't flat

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Will work for food
Supporting Member
Mar 6, 2011
Went to look at a new home to advise the home owner. An electrician friend recommended me. Looks like three supporting beams across the 30' width of the home. The center one is high or the engineered beams have sagged.
All I had with me was my 4' angle aluminum to check for flatness.
I placed my 4' straightedge across the peak where the center support is.
With the straightedge centered, the ends were about 1/4" off the subfloor.
The subfloor is t&g OSB, most likely 3/4" thick.
Sanding 1/4" off the 3/4" thickness of the OSB feels wrong even tho there is a support beam directly under it.
I didn't pay close attention to his flooring but it's an engineered hardwood at least 3/8" thick, maybe 7/16" or 1/2"....not sure.
Being it's over OSB, it would have to be floated, right. I believe he was going to staple it. If stapled, what's gonna happen if it ends up having to go through 1/4" of cement based floor patch?
Just advising, but he'd like me to prep the floor too.
Its a nice new home, on a hill overlooking the bay, not a cheap one.


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If they want mechanical fasteners then you'd be best off layering felt paper in the low areas.
Layered felt 1/4" deep? 🤯
...on each side of the beam 🤯
I'll call him after Christmas to see how his conversation with the builder went.
I have my new shop vac, my new Dust Deputy and a Lazer show to booot? 👍
...add a hardwood edging sander to the mix with some 16 grit paper and I might even impress myself. 😁
..... Of course I'll have to wear some new jeans and wash my truck. Might as well put on the full show. 😁
I haven't talked to him since I first saw the job and I'll have to wait to hear from him and what happened between him and his contractors conversation.
When I hear back, I'll bring back some more information and some photos which I didn't take originally.
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30# roofing felt is 1/32” thick. Up to 6 layers is approved. That gives you 3/16 worth of build up. Any more than that and you should be looking at using door skins or 1/4” ply to build things up.
When installing a 2nd layer of plywood I’ve been known to throw some roofing shingles underneath in the dips to bring it up to spec.… I’m not sure I’d try that directly under the finished floor though...😎
I've always been scared of roofing felt making noise. I once worked in a home and the underlayment wasn't properly nailed. It was half inch plywood over it 2 1/2 in engineered decking material.
The house was empty, not lived in when I went over to look at it and when I walked on the floor I could hear a crackling sound as the plywood stuck and unstuck itself to the roofing paper. The nail pattern was probably a foot apart. To be fair, the house wasn't heated at the time and was probably 50° in the house but still that sound has always scared me. Maybe put a layer of parchment paper in between each layer of roofing felt?

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