damp issue and how to use a moisture metre

but just been reading that the ideal humidity level is between 40-60% .

It depends really.

You don't want lower than 30% as that is uncomfortable and some say unhealthy.

At around 30-40% you should not be getting condensation, and if you do you really need to think about increasing or improving the insulation as you need unreasonably cold surfaces for condensation to occur. This low level of humidity is hard for some households to achieve, particularly older properties.

40-50% is a happy medium, it is not too hard to achieve, and condensation should be reasonably manageable, though it will still occur on single glazing, or cold bridges caused by lintels or uninsulated window surrounds.

Higher than 50% and it starts becoming harder to avoid condensation unless you have fairly modern levels of insulation and not much cold bridging.
 
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but just been reading that the ideal humidity level is between 40-60% .

It depends really.

You don't want lower than 30% as that is uncomfortable and some say unhealthy.

At around 30-40% you should not be getting condensation, and if you do you really need to think about increasing or improving the insulation as you need unreasonably cold surfaces for condensation to occur. This low level of humidity is hard for some households to achieve, particularly older properties.

40-50% is a happy medium, it is not too hard to achieve, and condensation should be reasonably manageable, though it will still occur on single glazing, or cold bridges caused by lintels or uninsulated window surrounds.

Higher than 50% and it starts becoming harder to avoid condensation unless you have fairly modern levels of insulation and not much cold bridging.

It must depend a lot on the house, materials used, temperature, lifestyle etc because we have a damp problem in our c1901 house due to damp clay soil under tHe floor, a gutter that's been leaking for years probably, and not enough under floor ventilation.

Our humidity is 65 - 75 in the good bits of the house and 80 in the most problematic areas. We have no mould or condensation on the walls. The only window condensation we get is right up in the loft on the velux.

I would have thought a humidity of 30 per cent or lower would cause sore eyes and nosebleeds! The humidity *outside* my house very very rarely drops below 45.
 
Yes, pretty much depends on lots of things, the porosity of materials and breath-ability of the construction will change how the house behaves.

Still, A 65-75% Humidity still needs approx 14c surface temperatures for condensation to occur, which kind of shows you the poor quality of UK stock when you consider how many properties suffer from condensation.
 

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