Securing Plywood To Floorboards

chamois | 12:52 Sun 02nd Sep 2018 | Home & Garden

6 Answers

The wooden floorboards in my daughter's bedroom are very uneven and not suitable for carpeting right now. I intend to cover the floor in 3mm ply using 8 x 4 foot sheets cut to fit and then carpeting over the top. What I'm not certain about is how to secure the ply to the floorboards, which are about 30mm thick softwood and the usual width.

Would ordinary countersunk woodscrews be OK for the job given the thickness of the ply? How far apart on the ply should the screws be placed and would you advise cutting the the ply down to more manageable sizes before securing to the floor? Are there any adhesives out there that might be better for the job?

Thank you.

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Red Robin Topiary Tree

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The Builder

I'm only guessing at the degree of uneven-ness of the floor, but I'm not sure this is the way to go.
If the ply is fixed tightly all over, it'll simply follow the dips in the floor. Meaning that you'll be no better off.

If the ply is fixed at the high spots only, and allowed to float over the dips, then you'll sink into those depressions as you walk.

Most uneven-ness can be dealt with by using a heavy duty underlay under the carpet. In fact, if you have substantial mountains and hollows, then an extra cut piece of underlay could be used to fill up the hollow before the proper underlay is laid.

This may seem over the top, but I would go for a latex-based floor leveller. There are some that can be laid to a good thickness.

Ryzen

If you have 30mm floorboards and they've sunken I would say you need to take a few up to find out whats going on below with the joists.Try not to cover with ply as it will be difficult in future if you need access to cables/pipes etc.

Arrods

Also, if you do down the plywood route, make sure you don't inadvertently screw into underfloor pipes. A while ago, just trying to screw down a loose floorboard, I did just that. The resulting leak materialised some months later when the screw rusted through.