28-08-2012, 04:51 PM
Glad you enjoyed Jeff's writings. He is often accused of having strong views on subjects like this (don't ask him about rising damp!), but I think that he speaks a lot of common sense and simply has to be strong with his opinions in order to be heard above the vested interests of the various damp-proofing and timber treatment companies. I read his column in the Telegraph each week and have one of his books.
http://www.telegraph.co.uk/property/prop...effhowell/
Since buying a Victorian house, I've had to spend a lot of time understanding these sorts of issues. Something which really helped is a combined thermometer and hydrometer that also calculates the due point - this lives in the cellar.
For air of a given temperature and a given relative humidity, it will have a "dew point". This is the temperature at which the water vapour carried in the air will condense back to liquid water. The most obvious analogy here is the pint of beer; remove beer from fridge and pour into a glass, and within seconds, the outside of the beer glass is wet with condensation...
In my cellar, now that I know the prevailing dew point, I can point my infra-red thermometer around and anything that is at or below that temperature will have condensation forming on (or in) it. Items that are lower down, hence colder, normally have this - especially if they are metal. The bottom of the walls are colder, so indeed have condensation forming on them. Interestingly, when cold walls attract condensation, most surveyors cry "rising damp", but in most cases it's condensation caused by not having the heating on for long enough (salts analysis is needed to distinguish between condensation and rising damp). Damp walls have very poor thermal performance, so this is a "catch 22", because they will conduct more cold from outside (or the cavity), which in turn attracts more condensation!
Anyway, condensation is the most under-diagnosed problem with housing today. We are forever being exulted to improve insulation and stop draughts, but this causes the relative humidity to rise to surprisingly high levels - high enough to put timbers at risk of attracting wood-worm. For that reason, I tend to buy thermometers that also measure humidity, and keep an eye on both.
In my leaky old house, it's generally pretty good. It's been a lot better since I fitted my new boiler last year, which runs all day during the winter, but provides gentle background heat at a level that depends on the outdoor temperature. And running gently continuously rather than roaring for two hours twice a day actually uses less fuel, but that's another conversation...
But, some of the most humid houses I know are very new houses, that have to be built to be practically airtight. People might be warm in them, but they are slowly suffocating and suffering from respiratory diseases. We are finally catching up with this, and whole-house ventilation/heat recovery systems are coming onto the market, but are currently very expensive.
I'm waffling.
But if you're interested, this is another very good read: http://www.pdoyle.net/content/view/42/46/
All the best,
Mark
http://www.telegraph.co.uk/property/prop...effhowell/
Since buying a Victorian house, I've had to spend a lot of time understanding these sorts of issues. Something which really helped is a combined thermometer and hydrometer that also calculates the due point - this lives in the cellar.
For air of a given temperature and a given relative humidity, it will have a "dew point". This is the temperature at which the water vapour carried in the air will condense back to liquid water. The most obvious analogy here is the pint of beer; remove beer from fridge and pour into a glass, and within seconds, the outside of the beer glass is wet with condensation...
In my cellar, now that I know the prevailing dew point, I can point my infra-red thermometer around and anything that is at or below that temperature will have condensation forming on (or in) it. Items that are lower down, hence colder, normally have this - especially if they are metal. The bottom of the walls are colder, so indeed have condensation forming on them. Interestingly, when cold walls attract condensation, most surveyors cry "rising damp", but in most cases it's condensation caused by not having the heating on for long enough (salts analysis is needed to distinguish between condensation and rising damp). Damp walls have very poor thermal performance, so this is a "catch 22", because they will conduct more cold from outside (or the cavity), which in turn attracts more condensation!
Anyway, condensation is the most under-diagnosed problem with housing today. We are forever being exulted to improve insulation and stop draughts, but this causes the relative humidity to rise to surprisingly high levels - high enough to put timbers at risk of attracting wood-worm. For that reason, I tend to buy thermometers that also measure humidity, and keep an eye on both.
In my leaky old house, it's generally pretty good. It's been a lot better since I fitted my new boiler last year, which runs all day during the winter, but provides gentle background heat at a level that depends on the outdoor temperature. And running gently continuously rather than roaring for two hours twice a day actually uses less fuel, but that's another conversation...
But, some of the most humid houses I know are very new houses, that have to be built to be practically airtight. People might be warm in them, but they are slowly suffocating and suffering from respiratory diseases. We are finally catching up with this, and whole-house ventilation/heat recovery systems are coming onto the market, but are currently very expensive.
I'm waffling.
But if you're interested, this is another very good read: http://www.pdoyle.net/content/view/42/46/
All the best,
Mark
