I am installing 5/8″x 3 5/8″ pre-finished flooring in a room with a 7/8″ hump in 4 feet running perpendicular to the lay of the flooring(a foundation wall in the finished basement beneath is responsible). The subfloor is 5/8″ particle board over 3/4″ 5 ply. I chose to lay on top of the particle board due to myriad problems including homeowner budget.
In order to flatten the hump, I was thinking of cutting out the underlayment 4 feet on either side of the hump and shimming with dimensional lumber ripped and planed in diminishing sizes and glued/stapled every 8″. I dry layed a bit of flooring over a similar setup and I couldn’t feel any deflection. Is the 7 1/4″ span doable? Should I lay sand or cinders in between?
I’ll post this to the hardwoodflooring.com forum, too.
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If I understand your situation correctly, there is particle board over the 3/4 plywood subfloor. I would sand and/or plane the hump until all is level, even if you lose 1/8" of ply. If you are nervous about the strength, you could lay 2x blocking under the subfloor, tack, then screw from above.
As for shims, I shimmed a dip a while back, screwed everything solid and the result was still squeaks.
I hope you mean it's OSB, not real particle board. PB makes a poor underlayment for nailing down wood flooring.
I'm sorry, I thought you wanted it done the right way.
Yes, it is particle board, There was a miscommunication early on. I was surprised to find 800 sq ft of particle board next to the pile of flooring when I arrived. I explained the risks to the homeowner and explained what needed to be done so.....I lowered the air pressure and doubled the stapling schedule...one 2" staple every 6 inches, that gives me 1/2" penetration into the 3/4" ply beneath the particle board (non-APA rated MDF, I beleive, so glue down wasn't a viable option either). 15 lb felt for a VB to the finished basement beneath. I'm banking on the Bamboo being as stable as is claim so that the staples don't get pushed and pulled too much.Oh boy...heavy sigh.