Hi ,we moved to civray 2 weeks ago.We love the house ,but have a problem that we did not know was there. The house is a metre away from a rock,which twice as high as the house,any water that comes down the rock just goes to ground,which seams to always hold water.When we shut the windows,the downstairs floors get wet.if we move a obstacle it is dry underneath,which tells me it could be condensate…I am not a builder,and would appreciate any ideas. Thanks BILL
Yes Gordon, because one is a cure for the problem and the VMC is a possible cure for the symptom. Not just a new membrane, insulation to cause a break in the termal conductivity. If the outdoor humidity is higher than indoors you will bring in more moist air and more will condense on the concrete slab. If you are extracting then you remove moist air and cause some drying but you mention redecoration which sound like more humidity and a possible mould issue to which the VMC is the ideal solution. The concrete slab is the condensing surface so a slightly different issue. I am not playing down the value of a VMC but in an old property the issues are different and buying a relatively cheap humidity meter to look at the issue would be a start.
Modern houses are spec'd with VMC's because of their higher insulation level so less condensing on surfaces but higher humidity due to being more air tight. The VMC stops the humidity and mould issues but only if you leave it on as you found and at around 15w-35w just how much does one need to economise? :-)
The amount of water that actually condenses on our slab floor is just enough to make the top damp so mopping is not a solution. Opening the garage doors increases the moisture over a larger area due to more moist warm air from the garden entering the garage and condensing.
You originally suggested breaking out the concrete floor and putting in a new membrane - fitting a VMC is thousands of euros cheaper!
We had gites which suffered from the same problem when I tried to economise by leaving the VMC switched off when they were not occupied. Leaving it on all the time cured the need for constant mopping up and redecoration.
In creasing ventilation and if possible adding heat is the solution for condensation. VMC units are now compulsory in all new houses.
Before spending out on a VMC and all the installation, get a humidity meter and check the humidity indoors and out. No point in installing something that just moves the same amount of moisture from outside to in and vice versa. Very high humidity everywhere in this glorious weather so a VMC would do very little against the cold concrete slab condenser.
No one retires in France!
Fit a ventilation extract fan -( called a VMC) in the ceiling venting to the outside - and leave it on 24/7 - it uses about the same power as a light bulb.
A drained ditch like the one shown at this link might help?
Thanks for answers,This morning ,no wet floors ,so it is condensation(warm air meets cold)plus i need to channel water from house.Just what i wanted in my retirement,but i am happy with a challenge. Bill
Agreed Mike, providing it's penetrating damp. Ours isn't, it's warm air meets cold concrete floor so water condenses and makes the top surface damp. Only by ventilation/de humidifying or putting in a thermal break with insulation can you prevent it.
You can purchase a pour-on permanent damp proof course from the UK (because it is a lot cheaper than in France) and that will stop all water coming up through the concrete. You can leave the finish as is or tile straight on top of it.
Rgds, Mike L
We have the same problem in our bathroom. The steam from the shower runs down walls, floods the floor and in truth our only option will be to strip the floor, relay it sloping into a drain and put in a fan to aerate/dehumidify. We have lived with it for four years but this year has been the limit. At least none comes in from outside, so if you have that problem a damp course, membrane or under house drainage resolve go for it.
A dehumidifier might help.
Yes Bill, it sounds like condensation, the warmer the air the more the water condenses on the concrete. We suffer the same in our garage. Ventilation will help unless you feel like breaking out the concrete, putting in a damp proof membrane and some insulation and re screeding the floor.