Repairing or replacing old floorboards to remove bounce

[paro]

Hi All - I am starting to fix up the inside of the old cottage now, nothing too heavy really just sanding painting and carpets really. That said the floors upstairs are in poor shape and was looking at ways to take out some of the flex in them. The first floor sits on top of a mix of flooring (all timber) with the weight bearing on some very old oak beams (probably original given the state of them). The top layer of this hodgepodge of timbers are some newer looking regular looking floor boards. The issue I have is these either have to be replaced or repaired and I'm not sure repair is an option.

 

My current thinking is to rip them out and replace with some 18 or 25mm ply in the hopes that load would be spread out and reduce the flex but having never done this I am not sure what the best way to go is.

 

Thanks, Paul

[ProDave]

Pictures?

 

Are you concerned with "flex" as in the floors have sagged over time?  OR "flex" as in you can see them bend and flex as someone walks on them?

[saveasteading]

2 hours ago, paro said:

replaced or repaired

More info please on the dimensions and materials of the joists, and of the floorboards.

Also the centres of the joists. Approximate will do.

 

Is it deflecting worryingly or simply uncomfortably?

As a guess do you think it is perhaps a few mm or more than that?

 

Presumably the bounce is greatest at mid span of the joists. Can you test that please, as it should be much less nearer to the ends.

 

I had this in an old house, and it would have been bouncing for centuries,  but is no longer what we expect and we had to get building regs on it for some reason I can't recall.

So the answer was to replace the floorboards with structural ply fixed with lots of nails  (but it could be screws, which would make it removable.)

This turns the composite result into  a series of T beams, where the plywood acts as a flange on top of the joists, and is massively stiffer. Floor boards do not do this.

It is a calculatable thing. and needs lots of fixings. From memory we had ring-shank nails at 100mm centres.

 

We should cherish old structures, but replacing the boards is usually acceptable.

 

This is not difficult to do, but I'd advise getting professional (Structural Engineer) input as it isn't reversible without damage, and there may be other issues.

This may also aid selling-on as a good Surveyor may notice it and want proof of the integrity.

 

[paro]

I should have given more info. So supporting joists (oak) are circa 18" apart. Looks like unlike the other room that I decorated a couple of years ago this floor has a differnt construction.  Room is approx 3m x 2.5m.

 

The floorboards are laying directly onto the beams shown.  The floor has always had a lot of flex/movement. Not in a concenred its not safe way, just more comfort and noise. I think it's a combination of the deflection in the boards and them moving around because they are not as secured to the joists as they once would have been. There are a few damaged ones as well which I am guessing is due to them being lifted  over the years for plumbing and eletrcial works which are running through the room.

 

There is no noticeable extra deflection in the middle.  I suspect its always been a bit bouncy since that part of the building is going to be a couple of hundred years old at least.

 

 

 

 

[ProDave]

Those joists are not very big and quite possibly full of woodworm.

 

My BIL lives in a 300 year old Welsh farmhouse like that.  All the rooms have a permanent dip towards the centre of the room and they all move as you walk on them.  But the surveyor summed it up verbally to my BIL (not what he put in writing)  It was built 300 years ago out of rocks and s**t, it hasn't fallen down yet and unlikely to fall down any time soon.

 

Another friend who had such a house lived the first 5 years with an Acro prop in the middle of the living room because he did not believe the floor above would take the weight of a double bed.  It did not collapse when he eventually removed it.

[paro]

I've been treating everything for woodworm and rot as I've been going round. One of the joists in the far corner is not in great shape and I don't think I'd want to jump up and down on it. Replacing the joists is a non starter though I think. If I try to touch them I will need to get BC involved and pretty sure I won't be able to replace like for like which means I'm either raising the floor or lowering the ceiling. Neither of which I want to go near. Worse case I can just go round and refasten the existing boards. I just wanted to see if replacing with ply would make a better job in terms of the flex / movement.

 

How about some extra dense heavy duty underlay as a half way. There must be something out there with a lot of mass designed to help absorb and spread the impact. -- Mass loaded vinly was what I am thinking of. 

Edited 10 hours ago by paro

[Nickfromwales]

2 hours ago, paro said:

I've been treating everything for woodworm and rot as I've been going round. One of the joists in the far corner is not in great shape and I don't think I'd want to jump up and down on it. Replacing the joists is a non starter though I think. If I try to touch them I will need to get BC involved and pretty sure I won't be able to replace like for like which means I'm either raising the floor or lowering the ceiling. Neither of which I want to go near. Worse case I can just go round and refasten the existing boards. I just wanted to see if replacing with ply would make a better job in terms of the flex / movement.

 

How about some extra dense heavy duty underlay as a half way. There must be something out there with a lot of mass designed to help absorb and spread the impact. -- Mass loaded vinly was what I am thinking of. 

The best thing for sharing the loads out is to stick with real wood floorboards with tongue and groove joints, ideally full boards or very long lengths. 

 

Nice fat screws, and keep the joints towards the first and last 1/3 of each row. 

 

You can get these reclaimed if you look at the rec’m yards online.

[Nickfromwales]

IMHO, those beams and joists look plenty good enough. 
 

I worked in a 200yr old cottage in Gloucestershire, and when re plumbing I quickly lifted a floorboard to look into the void below, searching for flow and return. 
 

I lifted the board, and the client who was sat in the kitchen downstairs, looked up at me and said “hello”. 
 

There was no void   “D’oh!”.

[saveasteading]

3 hours ago, paro said:

just wanted to see if replacing with ply would make a better job 

I believe that is what I have explained. If it isn't clear please say.

 

3 hours ago, paro said:

There must be something out there with a lot of mass designed to help absorb and spread the impact. 

That's not how it works. A mass will put a permanent bend on the joists.

underlay will reduce impact but not deflection.

It is physics / engineering and as Scotty said: ye cannae change the laws of physics. 

Ply for deflection reduction. Accept that old buildings move.

 

But if it is deflecting close to the support walls that is something else, movement of the bearing ends.

[paro]

Thanks. I do appreciate that it's very old and am trying to do an honest job in restoring things as best as is reasonable.   I'll try the ply approach first. I have a some sheets left over from an over order last year, failing that I'll search out some new boards. 

 

4 hours ago, saveasteading said:

But if it is deflecting close to the support walls that is something else, movement of the bearing ends.

 

I don't think this is an issue, with the exception of the one beam they all seem to be doing pretty well.  When I bought the property I did pay a bunch of money for a 'proper' inspection just because I knew it was a lot to take on. None of this was flagged. That said the whole report was a bunch of non-committal mealy mouth weasel words that gave me nothing substantive at all.

[saveasteading]

5 minutes ago, paro said:

I have some sheets left over

 Don't be too stingy on this, however much I approve of using spare stuff.

It needs to be strong plywood and I'm thinking 12mm structural ply. About £30 a big sheet or less if you shop around. . and the ring shanked nails for some reason were deemed better than screws .

https://www.wickes.co.uk/Structural-CE2%2B-Plywood-Sheet---12-x-1220-x-2440mm/p/252241