Suspended timber floor vapour barrier?

[pmcbythesea]

1977 bungalow, suspended timber floor over site concrete 75mm below joists (plumbers just love crawling about in there).

 

Okay, so we've pulled up the floorboards, cleaned up underneath (yes, really!), lagged the plumbing with extra glass fibre, and put in 100mm Celotex GA4100 between the joists with more glass fibre stuffed into any gaps around the perimeter. Original idea was to tape across joists and all Celotex joins but when we looked at that we thought a vapour barrier would be easier. (Ha, if only.....) Anyway, our friendly local BCO was out to have a look and I posed the question do we really need a vapour barrier. A certain amount of discussion ensued involving possible condensation (would be under the Celotex and just drip onto the subfloor) and any above floor leakages. The eventual conclusion was not to fit the vapour barrier because potentially that could just act as a pond collecting water which would rot flooring, kitchen cabinets and the like because the water would have nowhere to run. I think I am okay with that but I just wondered what you may think? It seems this goes against much of the advice I have come across. 

[Crofter]

Hi, I went through the same thought process on my new build- initially seemed a bit odd to omit the barrier layer on the floor when I will have one on every other surface.

I have decided to rely on the integrity of the T&G chipboard with glued joints. There will be a further layer of solid flooring glued down on top of that.

Like you, I was unhappy with the idea of a layer of plastic under the floor, with no possibility of any drainage.

[pmcbythesea]

Hmm, that's interesting, pleased I'm not the only one. 

[tonyshouse]

I find it most odd that a vapour barrier is used in walls and ceilings but not for floors.

 

I have installed lots of vapour barriers in floors and never had any problems, water from any leak needs to be sorted out and any left on top would soon disappear through evaporation or diffusion, it can't stay.

 

I particularly like using vb as air tightness barriers too and trapping them behind skirtings (where lots of draughts occur)

 

 

Edited August 2, 2016 by tonyshouse

[pmcbythesea]

Yes, that was what I understood too. However we've gone with the BCO and stuffed glassfibre around all the wall edgings so we should be draught-free. Now that the flooring is down it does feel more comfortable in that room (kitchen) - there was certainly a strong airflow under the joists and there's no sign of that now.