Relative Humidity

[treds1]

Apologies if this is the wrong place for this question but could not find a more suitable location.

About 6 weeks ago i found mould caused by condensation in several areas of my house, as we have only moved in relatively recently it got a damp pro to check things over and they checked for rising etc, and deduced that this was not a problem and it was caused by a high relative humidity and we should ventilate etc.


Since then we haven't really had any problems, and have stopped drying cloths inside as much as possible etc, fitted thermostat and maintain a temp of around 18-19 degrees c.
I purchased a cheap hygrometer and this normally shows a reading between 65 and 72, which by everything i've read online is really to high and should be around the 50% mark. Am i expecting too much trying to reduce the RH to this level in a 150 year old cottage? I also borrowed a dehumidifier and if left on over night or all day will reduce the RH by a few % over night and pull out a litre or so of water. But if i turn it off the RH seems to go back up fairly quickly. Could this be caused by moisture in the fixtures and fittings that is evaporating back into the air? though things don't seem damp to me or could the hygrometer be faulty?

Any ideas on what else i should be doing?

Thanks

Nick

 

[Burnerman]

Having a property of such age is sure to have humidity issues, I would think...after all, there can hardly be such things like waterproof membranes under the floors, etc.
In days gone by, homes were much draughtier and therefore better ventilated - especially as people relied on open fires, etc.
I think the only real way to improve things is to keep using your dehumidifier, and ensure that bathrooms and the kitchen have suitable extraction.
If you lift carpets up, is there a bit of a musty smell?
Similar issues with some of the properties around me!
John

 

[treds1]

I was guessing that that was probably the case, have lifted the odd bit of carpet and don't remember any musty smells but will check again. How much do people ventilate over the winter, have been advised not to have windows open to much as this will obviously reduce temp quickly, I don't have trickle vents but do have an option on the handles to leave open a few mm which i do during the day. Should I be opening some of the windows more?

 

[Johndug]

I think you're worrying unnecessarily. I have two hygrometers in the house and one of them has a "normal" range marked on it as being from 45 to 70%. At the moment one in the lounge is reading 75% but I'm not surprised because the density outside is currently 93%. It's chucking it down!

Your "cheap" hygrometer also may not be too accurate. If it has a hole in the centre at the back and you can see a screwdriver slot, that is an adjustment screw. Try standing your hygrometer on a damp cloth for a while so that it indicates 100%. It may be that you can turn down the screw slightly with the pointer still showing at maximum.

 

[ajrobb]

Condensation is usually worst near the floor, on external corners and behind large items of furniture. Try your hygrometer in these 'problem' areas. At this time of year, the outside humidity is often 100%, so you need to keep a reasonable temperature differential (house at least 5°C above outside temperature) to drop your internal relative humidity and keep internal surfaces at least 5°C above dew point. Ventilation without heat does not guarantee freedom from condensation. Generally, you need both heat and ventilation.

 

[foxhole]

You just need plenty of ventilation, you cannot dry washing in a house without problems, an old house will have a fireplace, is it open? if not it should have a vent.Heating does not help, hot air supports more moisture than cool air.Should have mechanical vents in bathroom and kitchen vented outside and should be in use at every opportunity.
Humidity levels rarely get to 50% except in summer or with air conditioning.