Replacing dodgy floorboards before laying vinyl

I'm planning to fit vinyl in my hallway (probably 4mm thick in total with a foam backing) and cork tiles in my living room and bedroom (also 4mm thick) and I guess I need to keep the levels between rooms fairly even.

In the hall there's a few places where the floorboards have been cut into smaller sections when installing gas pipes (when the flat was converted from storage heaters to GCH) and so on, and there's severe unevenness between the boards in those areas. There's also quite a bit of squeaking. So I thought of lifting all the T&G boards and replacing them with large cuts of 18mm plywood instead.

The advantages as I see them are that a larger board would distribute any weight across more joists, would require less fixing (screws instead of nails to reduce squeaking) and eliminating the T&G would mean there'd be less rubbing between boards (again less chances of squeaking).

I've knocked up a diagram of what I had in mind in Sketchup


I've indicated the first few joists roughly (obviously they're much wider) in red lines. The first one is 5cm in from the right wall, then they're spaced 18.5cm, 42cm and 39.5cm apart, measuring between the nails. After that they're all somewhere between 39 and 48cm apart.

I was thinking that each board (represented by the yellow and brown sections) would have half of it's edge screwed to the joist and the other half less wide and not screwed to the joist (but still resting on it) to leave enough space for the adjacent board to be screwed to the joist.

So in the case of the first (yellow) section by the front door, the upper left edge would be wider and screwed to the joist, with the adjacent (brown) section edge just resting on the joist, whilst the yellow section's lower left edge would be resting on the joist, with the adjacent brown section's edge screwed to the joist.

If that wouldn't work, perhaps I could screw noggins to either side of the joists and screw the boards down onto those?

Or maybe I should just lay hardwood on top of the existing floorboards to provide a level surface for the vinyl? My concerns about doing this are that the height variations between some of the floorboards might cause the hardwood to bend into the space (there are also some boards that are bowed upwards but I guess I could sand them down flat) and it would also force me to lay hardwood in the living room and bedroom to keep the level the same everywhere. I may need to sand down the living room floorboards before laying the cork tiles as there are several that are bowing up (not sure about the bedroom yet as I can't see the floorboards) but if I have to lay hardwood everywhere to bring the level up it's obviously going to increase the cost (although I don't know how much a suitable hardwood might cost yet).

 

Vinyl usually has a 1/4" under layment [plywood/osb] installed first. It should not be installed directly over the sub floor or hardwood. IF the existing floor is solid, I'd just install the 1/4" over it. Loose boards need to be fastened down first. Cupped/warped boards might need replacing.

 

Sorry, I think I mixed up hardwood and hardboard. I was thinking of using hardboard rather than plywood on top of the floorboards as a friend suggested it would be more rigid and thus cope with the unevenness of the floorboards better. Having read a bit more, it seems hardboard has issues with moisture and whilst it's not going in the bathroom or kitchen and will be covered with vinyl or cork tiles I guess it's probably safer to use plywood.

I will need to replace the worst parts of the floorboards first though, mainly in front of the airing cupboard where they've already been cut and perhaps in front of the bathroom and then sand down a few other spots.

For the living room/bedroom I'll probably just need to sand the floorboards before laying 1/4"/6mm plywood there too, so the rooms will be more or less level with the 4mm vinyl/cork tiles on top.

 

Another issue is dealing with any protruding nails. Some are sticking up enough to be able to get a clawhammer under to prise them out but others aren't but are still sticking up enough to affect the level of any plywood I lay on top.

Whilst I could lift the boards to remove the nails, as they're T&G I'd have to first cut that to separate them from the adjacent boards and if I have to do that, rather than putting them back down with screws and having to fill the newly created gaps between them with mastic, it would probably be easier to just replace them with square edge plywood boards (either the same width as the floorboards or wider, depending on how many need lifting), so if it's possible to deal with the nails without lifting the boards it would seem preferable.

 

Can't you hammer the nails flush? maybe use a punch.

 

Yeah maybe. I was a bit concerned about whether the joists might have weakened in the 60+ years since these flats were built and if hammering the nails might be a bad idea but I'll see if I can punch them.

I don't think there's any risk of damaging the downstairs flat's ceiling at least, as it's a thick slab of concrete and the joists aren't resting on it anyway.

 

I want to screw down some of the floorboards to try and stop them squeaking but I've learnt from the ones I've already taken up that the nails aren't necessarily in the center of the joist, so I can't just put the screw between the nails as it might be near the edge and split the joist.

So how should I determine where the center of the joist (width ways) is? Will I have to just cut a bit of the tongue and groove either side of where the joist appears to be and then slide something in the gap either side and move it around until it hits the joist?

These screws are supposedly great at stopping squeaking Spax Flooring Screws 4.5 x 60mm 300 Pack | Flooring Screws | Screwfix.com but they're too long at 60mm as my boards are 18mm and the joists are only 35mm, so I'll have to use something like this instead TurboGold Woodscrews Double Self Countersunk 4 x 40mm 200 Pack | Woodscrews | Screwfix.com

 

While we aren't sure how the construction methods were done 60 years ago, and especially in the UK, our standard spacing for joists are either 16" on center or 24" on center. You convert to metric. If you have access to beneath this floor, just measure between them. THe Spax flooring screws are good for what you are doing, albeit a little more expensive than regular 2 1/2" x8 decking screws.