Filling between floorboards - breathability?

[info_45]

There seem to be quite a few posts about filling the gaps between floorboards. I like the idea of cotton rather than a resin filler, but can see that there are various different methods that people have employed.

I'm just wondering how this fits in with the idea of breathability/air movement? I have recently had a suspended floor insulated, careful to add additional air vents and just using a breathable membrane beneath and over rockwool (so not the vapour control layer that some recommend - I know that others don't recommend any kind of insulation at all!).

This means that there isn't really a draft coming up between the boards, and the boards are generally quite snuggly fitted anyway. A few of my other posts have described how all the boards were taken up in order to allow the removal of loads of builders waste.

Knowing that I've added insulation but not 'sealed' the floor with a vapour control layer, I am conscious that I don't think I want to be stopping the movement of air from beneath the floor entirely. Wouldn't filling the gaps do this? Do people mainly do it for the purpose of reducing drafts? And therefore if I actually want to keep some air movement I feel like it would be counter-intuitive to do fill in the few mm between the boards.

 

[Cubist]

If you are not finding any significant draughts then theres no real value to be had from filling the gaps between boards - particularly if they are snug fitting and perhaps also T&G. It can be a huge task requiring considerable effort rather than large direct materials costs. I would not bother - despite being a proponent of the use of Caulking Cotton for gap closure between timbers.

 

[fernicarry]

how this fits in with the idea of breathability/air movement

As you've used a membrane there shouldn't be any air movement even if there are gaps between the boards. Breathability refers to the movement of water vapour not air which your build up should still allow so all good. My boards have lots of gaps and apart from a couple of places where there was a danger of small children falling between them I've not bothered doing anything about it. I've put a breather membrane under most of the ground floor to control the drafts and some of it is insulated too. One of these years I'll get back to finishing that particular job...