Strengthening tongue & groove chipboard floor

[SouthLondonCharlie]

I'm in the process of having a loft conversion done by one of the big loft companies, who have laid standard tongue-and-groove chipboard floors. These are used throughout the rest of my 20-year-old house and have lost strength and become squeaky and bouncy in lots of places. I'd like to prevent this happening in the loft by screwing plywood on top. Can anyone advise if this will help and if so, what grade of plywood? For the loft bathroom, I might skip the ply and use cement tile back board throughout the floor before tiling.

thanks

 

[JohnD]

chipboard has its uses. For example, it will make a good bonfire, and usually lasts until the builder has been paid.

18mm ply is much better. When you factor in the cost and effort of ripping out the old chipboard when it cracks and creaks, the extra cost is well worthwhile.

 

[SouthLondonCharlie]

The chipboard is already laid and I can't remove it without a major fight with teh builder and huge expense. So ideally I'd like to firm it up with ply. 18mm might overspec the floor and make it too heavy for the joists, so wondering if 9mm would be enough?

 

[JohnD]

If you wanted to strengthen it, noggins under unsupported joints would be the way to go, but now it's down, you can do that when it starts to crack and you have to cut out and patch bits. A multicutter makes the job much easier than it used to be. Use screws, not nails, as you can tighten them down when they loosen and start to squeak.

The problem with a ply overlayer is that it will be in the way when you need to mend the chipboard.

I've never tried it as a strengthener, I would have thought you'd need to bond it with glue, but I don't know.

You can guess that I have been enraged by the poor performance of chipboard in the past.

 

[SouthLondonCharlie]

I shouldn't need to mend it if the ply or ply+chipboard makes the floor solid. The reason chipboard eventually fails is that repeated bending under dynamic load of people walking on it between the joists eventually softens the fibrous structure. If something rigid is spreading that load to the joists (e.g. cement backer boards + tiles in a bathroom), the chipboard won't bend or fail. I'm just not sure what grade of plywood is enough. 18mm would certainly work but may be excessive. 9mm or 12mm glued and screwed might be enough.

 

[geraldthehamster]

The joists in the converted loft are probably better and deeper than the joists in the rest of your house. I wouldn't worry about it.

 

[Deleted member 174758]

Contrary to what John says correctly specified and installed chipboard won't squeak. The difficulty, as ever, is that far too many installers cut corners, and far to much low quality chipboard is installed on undersized joisting...... This isn't much help to the OP, however the tongues should all gave been glued and all the short (end) joints should also be supported on joists whilst the screwing should be at a minimum of 200mm centres on joists (150mm is better). If that is the case and the chipboard is of sufficient quality it should be a reasonable floor. I've done a lot of commercial t&g chipboard and the proper stuff properly fitted just doesn't result in call backs. Some of the domestic stuff I've seen is so obviously done in a hurry on a price by people who don't give a tinker's cuss that I am not surprised that there are chipboard haters out there. The building trade really does need to pull it's socks up on this one!

 

[JohnD]

Contrary to what John says correctly specified and installed chipboard won't squeak.

I'm not in a position to comment, since it appears I have never seen any.

 

[Deleted member 174758]

Throw away comment?