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Fixing T&G floorboards - where to gap?

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Fixing T&G floorboards - where to gap?

Postby RogerS » 10 Nov 2014, 18:16

Everything I read about laying floorboards talks about having an expansion gap around the perimeter of the room but to my mind that is just plain daft. How is it going to work if, as in my case, each board is screwed down through the tongue with Tongue-Tite screws? Surely if the board wants to move then it can't because of the screws.

So surely leaving a gap between each board makes far more sense although the purist in me wants to see them tight together.

But then you read about using floorboard cramps to get those boards nice and tight together.
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Re: Fixing T&G floorboards - where to gap?

Postby DaveL » 10 Nov 2014, 22:43

I think the use of clamps to get the boards tight was due the boards being on the damp side, so once they dry out the gap is not big enough to fall down.
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Re: Fixing T&G floorboards - where to gap?

Postby Newbie_Neil » 11 Nov 2014, 14:48

Hi Roger,

I have put new floorboards in all of the upstairs room and bought good quality T&G from Wickes. Ok don't laugh, it was excellent. :D

All of the boards were dry and so there are no gaps between them. Each floorboard goes under the skirting but didn't go through to the wall, thereby leaving a small "expansion" gap. I don't think that it would have been required, as the boards haven't moved.

They were all screwed down and then the carpet laid.

I'm sure that I needn't have spent as much on the T&G as I did, but I didn't want any problems.

Neil
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Re: Fixing T&G floorboards - where to gap?

Postby RogerS » 11 Nov 2014, 15:48

Thanks for the input, guys. I also asked the question over on UKW and I have come to the conclusion that the expansion gap recommendation is rubbish advice for individually fixed boards. This is what I posted.

Thanks guys for all the input. In my case the floorboards are KD oak. When they came out of the plastic wrappers fresh from the factory they measured just over 4% with a Wagner meter. A few days later they were up around 7-8% and have remained stable at that.

I can see the logic that they may shrink a bit more but TBH at that moisture content I think not. So the question arises as to whether they will expand and if so by how much (and assuming I don't leave an over-flowing water barrel on them!). And whether to have an expansion gap around the perimeter.


Here's my take. The expansion gap around the perimeter for boards that are individually nailed or screwed down is an old wives tale...passed down over the years without any thought as to relevance. My reasoning twofold. First, take my boards, for example. 200mm wide. Let's assume they each expand by 0.5mm. I've got 13 boards so it's also reasonable to assume that they all expand the same amount. So that's 6.5mm to accommodate. Let's start at the middle and work out towards the walls. The ones on either side of the central one need to budge up a bit more to accommodate the expansion needed by the preceding ones. So by the time you get to the each wall we are expecting that board to have moved over by 3.5mm. Which means that nail or screw is also going to need to move it's position by 3.5mm. Is that going to happen? I don't think so. And if it did, then what? That screw is going to be ripped out, the boards will never go back down flat again and so that expansion gap was pointless !!

Second, if this perimeter expansion gap was going to be of any use then at least somewhere down the line someone would have said 'For a room with width x metres you need a gap of 10mm, for a room of xxx metres you need a bigger expansion gap'. But they don't so QED.

The answer to my own question has, I'm embarrassed to say been staring me in the face. I have oak floorboards on the landing and in another bedroom that were laid 10 years or more ago. They were all fitted as tight to each other as I could get. None of shrunk. None have moved. Certainly no cupping of individual boards. Tight it is and only a perimeter gap where it helps laying the final board down.
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Re: Fixing T&G floorboards - where to gap?

Postby Mike G » 11 Nov 2014, 18:43

Hmmm....

Floorboards could expand without bending or breaking screws, simply by bowing the joists, or by leaning the screws over within the softwood of the joist (or a combination of both). Leaning the screws in the direction of the grain of the joists is trivially easy.

Guidelines such as this are written to cover all circumstances, not ideal ones. You may well have a perfectly sound environment for your boards, with stable temperature and relative humidity, but not all floors will be laid in such conditions. The regulations/ recommendations (whatever), therefore have to be written to cover the worst-case, rather than the everyday. Imagine a suspended ground floor with a small void, poor or no ventilation underneath, no DPM, a leaking pipe or waste, and intermittent heating above. Now, if you laid that flooring right to the walls, you could push your walls out, easily.

You can certainly, therefore, take a view on the risks of your floor ever falling into less than ideal circumstances. You may well be confident that it never will, and reduce the gap.......but I certainly wouldn't be reducing it to zero.
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Re: Fixing T&G floorboards - where to gap?

Postby RogerS » 11 Nov 2014, 18:59

Mike, if the floorboards moved that much and ripped screws out or bent joists (which I must confess I find very hard to believe) then not having a perimeter gap would be the least of my worries. That floor would be knackered - totally. The perimeter gap isn't going to help one bit.
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Re: Fixing T&G floorboards - where to gap?

Postby Mike G » 11 Nov 2014, 19:25

I'm not talking about ripping screws out....just pushing them over a bit.

Whilst decent joists are unlikely to be bowed by the flooring, some old suspended floors are laid on 3x2's on a brick straight on the ground, like a shed floor. The bounce is taken out by having a brick at half span, or even one at 1/3rd and another at 2/3rds. I have seen these bow upwards by almost a foot in the middle. Yes.......12". That wasn't entirely due to the floorboards expanding, but that was certainly a factor.

Imagine this, Roger. Imagine laying the boards loose on the joists (ie not screwed or nailed down). Fit them tightly together, and fit them hard up to the walls. Come back in 10 years, and what do you think you'll see?
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Re: Fixing T&G floorboards - where to gap?

Postby RogerS » 11 Nov 2014, 22:01

We're not comparing like with like. Of course there will be a difference if the boards are not nailed down. And yes you are correct if you are talking about 3 x 2 joists but in reality joists are much larger than that.
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Re: Fixing T&G floorboards - where to gap?

Postby Mike G » 12 Nov 2014, 11:21

Yebbut....

You're missing my point, Roger. My principle point is that the 10-mm-gap-at-the-edges rule was invented to cover the worst case scenario. In those circumstances, it is absolutely necessary. In yours, it may not be. However, that doesn't mean that in the ideal situation, or in your situation, or in any situation, zero gap is acceptable. That would be the equivalent of saying that in an ideal situation you could glue all solid panelling together into a frame, and the cross-grain scenario wouldn't be an issue. Well, in some extreme situations you might get away with it. In most, you wouldn't.

Anyway, why the problem? Any gap at all would be covered by skirting. Are you planning not to have skirting?
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Re: Fixing T&G floorboards - where to gap?

Postby RogerS » 12 Nov 2014, 16:02

Hi Mike, I think we are going to have to disagree to differ on this one!

Re skirting...TBH we are not great fans of skirting in a room with old oak beams. I'd be very disappointed with myself if I couldn't scribe a floorboard to within 1mm of a wavey wall !
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