Wednesday, July 1st, 2009
Chris Strogilis asked:
QUESTION: I am a little confused. You say that one of the measures to control internal humidity during the heating season is to ventilate. How can it be possible?
Exterior relative humidity most of the times is higher than interior R.H. Sometimes it is as high as 95-98%.
ANSWER: The misconception is between the meanings of the terms “absolute” and “relative humidity”. In order to achieve “dilution” of interior humidity we need external air drier on an absolute basis. Relative humidity as an index sometimes could be misleading because it strongly depends on temperature.
Let’s see a small example to make it completely clear.
In our beautiful Thessaloniki, North Greece, it’s not a rare phenomenon to have outdoor temperatures near 0oC. This means that even for a R.H. of 100% the absolute humidity or moisture load is 4,8gr/m3.
Coming to the interior rooms…
For an average temperature of 22-23oC the absolute humidity is about 14gr/m3. This is a much bigger number.
Actually for the heating season this is always the case: indoor absolute humidity is higher than outdoor. This means that by ventilating we can always achieve “dilution” of the interior humidity.
QUESTION: What is the most effective measure to prevent/control mold growth in home?
ANSWER: Mold growth is a moisture related problem. When you control moisture, you control mold growth. Potentially there exist many moisture sources etc. roof, façade and basement leaks, pipe leaks, moist air infiltration etc.
Humidity produced from every-day indoor activities is by far the more important moisture source under normal conditions.
So, do your best to reduce production of humidity by abstaining from certain “bad” habits (as for example drying clothes inside).
”QUESTION: I don’t have any condensation or mold problems in my wet rooms. No problem also in the room where we usually dry our clothes on the radiator. But I have problems in other rooms with no vapor production activities. Why?
ANSWER: Firstly we have to stress that water vapor can travel easily from room to room via open doors. So relative humidity can soon be equalized. Reasons for which condensation and mold develop in this special room might be:
1. This room is not ventilated properly.
2. This room is underheated.
3. This room has an unfavourable orientation.
4. And the most probable, there are thermal bridges in the external walls.
Other factors to consider:
- Are there some plants in the room?
- Is this a much-frequented room etc?
QUESTION: There are two identical apartments with the same orientation. I have mold and condensation problems whereas my neighbor who lives one floor above me has practically no problems.
ANSWER: Please check the previous answer. The apartments are identical in form but not in prevailing conditions. Possible differences (except for the above mentioned) could be:
- more people inside your apartment
- a baby maybe?
- adolescents who have baths 2-3 times on a daily basis
- clothes drying indoors
- unvented gas or kerosene heaters etc.
The moral is that two apartments however identical in construction terms, will always have marked differences in their prevailing conditions.
QUESTION: Can we alleviate mold and condensation problems by intervening externally?
ANSWER: If you mean some waterproofing measures, definitely no. The only possible external intervention could be the addition of some extra thermal insulation. Of course this could be done also from inside.
I ‘ve seen a lot of money thrown out of the window trying to solve these problems by external waterproofing.
Chris Strogilis
http://maconwaterproofing.blogspot.com/
New Cpr Guidelines
QUESTION: I am a little confused. You say that one of the measures to control internal humidity during the heating season is to ventilate. How can it be possible?
Exterior relative humidity most of the times is higher than interior R.H. Sometimes it is as high as 95-98%.
ANSWER: The misconception is between the meanings of the terms “absolute” and “relative humidity”. In order to achieve “dilution” of interior humidity we need external air drier on an absolute basis. Relative humidity as an index sometimes could be misleading because it strongly depends on temperature.
Let’s see a small example to make it completely clear.
In our beautiful Thessaloniki, North Greece, it’s not a rare phenomenon to have outdoor temperatures near 0oC. This means that even for a R.H. of 100% the absolute humidity or moisture load is 4,8gr/m3.
Coming to the interior rooms…
For an average temperature of 22-23oC the absolute humidity is about 14gr/m3. This is a much bigger number.
Actually for the heating season this is always the case: indoor absolute humidity is higher than outdoor. This means that by ventilating we can always achieve “dilution” of the interior humidity.
QUESTION: What is the most effective measure to prevent/control mold growth in home?
ANSWER: Mold growth is a moisture related problem. When you control moisture, you control mold growth. Potentially there exist many moisture sources etc. roof, façade and basement leaks, pipe leaks, moist air infiltration etc.
Humidity produced from every-day indoor activities is by far the more important moisture source under normal conditions.
So, do your best to reduce production of humidity by abstaining from certain “bad” habits (as for example drying clothes inside).
”QUESTION: I don’t have any condensation or mold problems in my wet rooms. No problem also in the room where we usually dry our clothes on the radiator. But I have problems in other rooms with no vapor production activities. Why?
ANSWER: Firstly we have to stress that water vapor can travel easily from room to room via open doors. So relative humidity can soon be equalized. Reasons for which condensation and mold develop in this special room might be:
1. This room is not ventilated properly.
2. This room is underheated.
3. This room has an unfavourable orientation.
4. And the most probable, there are thermal bridges in the external walls.
Other factors to consider:
- Are there some plants in the room?
- Is this a much-frequented room etc?
QUESTION: There are two identical apartments with the same orientation. I have mold and condensation problems whereas my neighbor who lives one floor above me has practically no problems.
ANSWER: Please check the previous answer. The apartments are identical in form but not in prevailing conditions. Possible differences (except for the above mentioned) could be:
- more people inside your apartment
- a baby maybe?
- adolescents who have baths 2-3 times on a daily basis
- clothes drying indoors
- unvented gas or kerosene heaters etc.
The moral is that two apartments however identical in construction terms, will always have marked differences in their prevailing conditions.
QUESTION: Can we alleviate mold and condensation problems by intervening externally?
ANSWER: If you mean some waterproofing measures, definitely no. The only possible external intervention could be the addition of some extra thermal insulation. Of course this could be done also from inside.
I ‘ve seen a lot of money thrown out of the window trying to solve these problems by external waterproofing.
Chris Strogilis
http://maconwaterproofing.blogspot.com/
New Cpr Guidelines
