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?

Are you gluing or nailing? Sounds like you intend on nailing. You know you're not supposed to install over p. board. That floor's gonna squeek real good after a while. But you don't care; you got paid, right? So your here knowing you're installing the floor incorrectly and you want us to help you do it? Give me a break!

Not to be harsh, but just straight up and to the point.


If your not going to do it WRIGHT, you have no business doing it at all!

Get rid of that particle board! If it is not in the budget, hardwood and the cost of installing it, is not in the budget.

Have you budgeted to do it twice? I bet not, it has not crossed your mind yet.


Cutting corners has put many wood companies into bankruptcy!

Nailing or gluing to particle board is gaurenteed to fail. The only thing We don't know is the exact day of failure. The "hump" only decreased the time the floor will fail.