High Humidity in Attic | Ask Mason Knowles - SPF Consultant | Spray Foam Technical Questions and Answers | SprayFoam Magazine Q&A Forums

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Protronics00 Posted: Sep 16, 2017 12:25 AM	High Humidity in Attic I had a new house built and had open cell spray foam installed on all exterior walls and roof rafter. When I moved in approximately 1 month ago I noticed the attic air handler was sweating excessively. By excessively I mean enough to have standing water in my drain pain and enough to have water dripping from my supply air plenum onto the attic floor. I placed a thermostat in the attic and I noticed the temperature runs 5-7 degrees warmer than the living space of the house. The humidity inside the attic runs in the low 60% to over 70% during the hottest part of the day but stays in the upper 40% to lower 50% in the living space. I live in south Mississippi so the humidity outside is 99% throughout the summer and part of the fall. We had a cold front last week which lowered the humidity substantially outside and also lowered the humidity in the to upper 40% during that time in the attic. I have a recovery ventilator installed in the attic and hooked to the return air plenum of the AC system. It runs independently and is set to run for 20 minutes per hour unless the outside humidity is more than 80% (which is all the time in the summer) it will shut off. I have had the AC contractor out several time to adjust fan speed, change inside insulation in the unit, install a shroud on the coil, and check freon levels. The unit works great and cools fantastic I'm just concerned about the humidity in the attic. What can you recommend to check or have the contractor check to fix the issue?
mason Posted: Sep 20, 2017 12:33 PM	It is not unusual to have higher humidity in the attic than in the living spaces of the house, but if it reaches 70% that is too much. I expect the temperature in the attic to be within 5-8 degrees of the living space. Try to reduce the moisture going into the attic. I would look at your mechanical ventilation in the house. Are you running the fans when you shower, or when cooking? Does it vent outside or into the attic? Do you have a lot of plants, pets, aquariums, etc that can produce a lot of moisture? How often do you wash clothes and run the dryer? Also, have someone run a blower door test on your house while checking for air gaps and voids with a thermal imaging camera. Perhaps those gaps and voids are letting in warm moist air in the attic that is increasing the humidity. Is the air handler and duct work insulated well so that it does not have condensing surfaces? You can run a fan in the attic, that helps evaporate the moisture.

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Protronics00

Posted: Sep 16, 2017 12:25 AM

High Humidity in Attic

I had a new house built and had open cell spray foam installed on all exterior walls and roof rafter. When I moved in approximately 1 month ago I noticed the attic air handler was sweating excessively. By excessively I mean enough to have standing water in my drain pain and enough to have water dripping from my supply air plenum onto the attic floor. I placed a thermostat in the attic and I noticed the temperature runs 5-7 degrees warmer than the living space of the house. The humidity inside the attic runs in the low 60% to over 70% during the hottest part of the day but stays in the upper 40% to lower 50% in the living space. I live in south Mississippi so the humidity outside is 99% throughout the summer and part of the fall. We had a cold front last week which lowered the humidity substantially outside and also lowered the humidity in the to upper 40% during that time in the attic. I have a recovery ventilator installed in the attic and hooked to the return air plenum of the AC system. It runs independently and is set to run for 20 minutes per hour unless the outside humidity is more than 80% (which is all the time in the summer) it will shut off. I have had the AC contractor out several time to adjust fan speed, change inside insulation in the unit, install a shroud on the coil, and check freon levels. The unit works great and cools fantastic I'm just concerned about the humidity in the attic. What can you recommend to check or have the contractor check to fix the issue?

mason

Posted: Sep 20, 2017 12:33 PM

It is not unusual to have higher humidity in the attic than in the living spaces of the house, but if it reaches 70% that is too much. I expect the temperature in the attic to be within 5-8 degrees of the living space. Try to reduce the moisture going into the attic. I would look at your mechanical ventilation in the house. Are you running the fans when you shower, or when cooking? Does it vent outside or into the attic? Do you have a lot of plants, pets, aquariums, etc that can produce a lot of moisture? How often do you wash clothes and run the dryer?

Also, have someone run a blower door test on your house while checking for air gaps and voids with a thermal imaging camera. Perhaps those gaps and voids are letting in warm moist air in the attic that is increasing the humidity.

Is the air handler and duct work insulated well so that it does not have condensing surfaces?

You can run a fan in the attic, that helps evaporate the moisture.

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