Breathable flooring over a sub floor?

[Lunarsyreni]

I have a 1700s converted horse stable property, it’s lime, stone and slate. I have completely removed a rotten subfloor down to the stone and lime sleeper walls, roughly a meter drop to a compact soil floor. My new subfloor will be c24 timber joists with 18mm caber (water resistant) tongue and groove, filled in with 150mm isover (breathable) insulation. I understand that my property must breathe so I have been taking steps to repair the property to its original materials. However I haven’t been able to find a good solution for the floor and my builder went ahead with the 18mm caber T&G. Will it be best I use a breathable carpet/tile/wood on top of the caber T&G or does the fact that the caber is water resistant completely void this? If this is the case, will it be best I install internal floor vents instead? There are a few external air bricks but not enough for good air flow.

Thanks in advance for any advice on this

 

[a twig]

More external air bricks would be the usual remedy?

 

[Lacan07]

I have a 1700s converted horse stable property, it’s lime, stone and slate. I have completely removed a rotten subfloor down to the stone and lime sleeper walls, roughly a meter drop to a compact soil floor. My new subfloor will be c24 timber joists with 18mm caber (water resistant) tongue and groove, filled in with 150mm isover (breathable) insulation. I understand that my property must breathe so I have been taking steps to repair the property to its original materials. However I haven’t been able to find a good solution for the floor and my builder went ahead with the 18mm caber T&G. Will it be best I use a breathable carpet/tile/wood on top of the caber T&G or does the fact that the caber is water resistant completely void this? If this is the case, will it be best I install internal floor vents instead? There are a few external air bricks but not enough for good air flow.

Thanks in advance for any advice on this

just out of interest which Isover insulation are you using?

 

[Cubist]

Will it be best I use a breathable carpet/tile/wood on top of the caber T&G or does the fact that the caber is water resistant completely void this? I

Seems pointless to me. The caber will not permit airflow through it so a breathable surface of any kind above it delivers no benefit at all.

If this is the case, will it be best I install internal floor vents instead?

Yes.

I always worry about the use of 'chipboard' where there is any possibility it may be exposed to heavy damp or water leaks. Once wet, it expands, loses its structural integrity and ultimately collapses. Also, when nails or screws are used to fasten down floor-boards on its surface these can disrupt the structure of the chipboard to reduce a very weak bond.

 

[CliffordPope]

I thought water-resistant was different from non-breathable?

 

[Cubist]

Happy to be proved wrong but, to my admittedly limited understanding of the chemistry associated with water resistant coatings, I would assume that these also severely inhibit breathability? If that assumption is correct, then it follows that a water resistant coating on the upper surface may trap moisture rising from below.

 

[CliffordPope]

I've no idea, but whenever I have queried why a water-saturated outer face of a wall could nonetheless be breathable to allow household moisture to escape, I am told by the experts that water permeability and water vapour permeability are different things.

 

[Cubist]

Thats the trouble with talking to experts - it always comes down to degrees and statistics. I guess that in this case it's to do with the degree of permeability of a given material when in contact with a substance in either its liquid or gas form. Unfortunately that leaves us lay people dependent on experts that often have more in common, in a behavioural sense, with a politician.