Insulation between joists Floor.. Membrane and sand Yes No

Hi, we are insulation between ground floor ( brethable membrane up and down joists and then insulation cellulose so all can breath,

we have a slab of concrete not sure how thick.

The question is should we put a membrane Not Breathable on the concrete and then sand to weight it down?

Had to read your post upside down to understand it. If the situation you have is a concrete sub-floor, with a suspended timber floor above, why put a membrane on the concrete?

Hi

I'm pinkofficelady's husband.

The semi-detatched bungalow we are in was built in 1929/1930 and due to the high water table, when it has rained the kitchen (3x2m area that sticks out of the back of the bungalow and has concrete sub floor that is lower than the rest of the bungalow) sub-floor ends up with 1 to 2 inches of water on it.

There are 6 air vents at the front (one on each side of the three sided bay window - e.g. 3 vents per bay and two bays). There are three vents on the side of the bungalow facing out to the shared drive and one on the rear, but where the kitchen sticks out someone has built two lean-tos, one at the rear and one at the side of the kitchen and has blocked the air vents in the sub-floor void in that room.

We know we have to add more vents, mainly in the kitchen and a couple more at the rear of the property, but the main issue is that the moisture in the void (which comes up at the edges of the concrete slabs) soaks into the joists and floor and things touching the floor from above go mouldy, and the carpet tiles we laid also feel cold and damp.

We are going to be lifting the floorboards, placing Tyvek Supro membrane (already bought) between the joists (probably replace the joists as I've crawled around down there before to fit central heating pipes and mains wiring and have seen a few have rot and woodworm holes, etc.) and then fill the spaces with thermofloc cellulose loose fill insulation (already bought), but before we do that would it make sense to do anything with the moisture that is coming up from below the sub floor, either by the method mentioned by my wife or some other way?

Any thoughts you could provide would be helpful.

Water on the sub floor is no problem. Many properties do not have sub floor-just earth. If your joists and floor are damp then the problem is either insufficient ventilation (likely from your description) or no damp course under the joists where they enter the wall.