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Humidity and open cell foam

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ckelly14

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Discussion starter · #1 ·
High humidity in attic after open cell foam install is a well-known topic and discussed in other threads.

I wanted to post my experience and see if anyone here had any thoughts.

I have a larger home (5000 SF, three floors) that had open cell foam installed 3 years ago. 2 years ago, we noticed significant humidity on the top floor and a significant musty smell. After consultation with an installer, we installed an Aprilaire 70 dehumidifier, but still recorded humidity levels up to 80%. The HVAC installer upgraded our dehumidifer to Aprilaire 95 a few months ago with better results with a set point of 54% but humidity up to 64-67% during the mid afternoon.

My concern is increasing outdoor humidity during the summer, although the days with highest humidity recording were days that were sunny with highs around 90. We are in coastal SC.

My installer sent me an article from greenbuildingadvisor.com that discussed this phenomenon and some experimentation showed that the humidity may actually be coming from the inside the house, not outside. I find this hard to believe but wondering how this changes anyone's approach.

Any comments or suggestions are appreciated.
 
#2 ·
How's the crawl space? Moisture is coming from somewhere, whether it be from outside or inside the house. HVAC systems may be oversized too if you applied foam insulation but retained the same capacity and this can impact their ability to dehumidify.
 
#3 ·
ckelly14 said:
High humidity in attic after open cell foam install is a well-known topic and discussed in other threads.

I wanted to post my experience and see if anyone here had any thoughts.

I have a larger home (5000 SF, three floors) that had open cell foam installed 3 years ago. 2 years ago, we noticed significant humidity on the top floor and a significant musty smell. After consultation with an installer, we installed an Aprilaire 70 dehumidifier, but still recorded humidity levels up to 80%. The HVAC installer upgraded our dehumidifer to Aprilaire 95 a few months ago with better results with a set point of 54% but humidity up to 64-67% during the mid afternoon.

My concern is increasing outdoor humidity during the summer, although the days with highest humidity recording were days that were sunny with highs around 90. We are in coastal SC.

My installer sent me an article from greenbuildingadvisor.com that discussed this phenomenon and some experimentation showed that the humidity may actually be coming from the inside the house, not outside. I find this hard to believe but wondering how this changes anyone's approach.

Any comments or suggestions are appreciated.
Click to expand...
Another article on moisture in the attic.

https://www.buildingscience.com/doc...ding-science-insights-newsletters/bsi-016-ping-pong-water-and-chemical-engineer

What is the roof material? A certain amount of moisture that condenses on the in the roofing material during the evening hours is driven through the roofing material and deck accumulates in the attic when the sun heats the attic also.

What is the %RH in home during the day and night? Do you have any fresh air ventilation? Have you tried a small amount of attic ventilation at the top? Was the moisture buildup similar winter and summer? Any condensation on windows during the winter? What do have, slab on grade, crawlspace, or basement?

You may have various sources of moisture. Occupants also generate moisture in a home also.

Answering the questions will provide clues for us to comment on.

Regards Teddy Bear
 
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Discussion starter · #4 ·
teddy bear said:
Another article on moisture in the attic.

https://www.buildingscience.com/doc...ding-science-insights-newsletters/bsi-016-ping-pong-water-and-chemical-engineer

What is the roof material? A certain amount of moisture that condenses on the in the roofing material during the evening hours is driven through the roofing material and deck accumulates in the attic when the sun heats the attic also.

What is the %RH in home during the day and night? Do you have any fresh air ventilation? Have you tried a small amount of attic ventilation at the top? Was the moisture buildup similar winter and summer? Any condensation on windows during the winter? What do have, slab on grade, crawlspace, or basement?

You may have various sources of moisture. Occupants also generate moisture in a home also.

Answering the questions will provide clues for us to comment on.

Regards Teddy Bear
Click to expand...
Thanks for thinking about this.

The roof is asphalt shingles. The third floor has living space in the lower central portion and attic space in the roof peak and sides. The living space is an in-law apartment that is currently unoccupied. The roof peak portion and the sides are contiguous with each other, and used to be an unconditioned, ventilated attic space prior to the installation of the open cell foam spray. That area is currently semi-conditioned, but it really only has one small supply and no return. The return comes from the living area. The HVAC equipment is in this space.

%RH for the home is maintained at 54% except in the afternoon on a warm sunny day when it climbs as described. No issues in the winter.

Perhaps setting the RH even lower at night would help with this accumulation?
 
#6 ·
Usually, when the underside of the roof is foamed...
The 'load' (necessary BTU capacity) of both heating and cooling... goes down significantly!
I have literally seen a house where 3T of AC was necessary before foaming...
Then 2T of AC was more than adequate after foaming.
(Note this is in Metro Atlanta, which is humid... however not as humid as a coastal climate).

I think your first concern... would be the size of the AC...
Smaller = more run time, which means better de-humidification.
 
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Discussion starter · #8 ·
The humidifier and AC seem to be on continuously and can't keep up. This is a 95 pint Aprilaire, which is performing better than the previous 70 pint. Maybe a 130 pint? I guess the return should be at the highest point of the attic, not where the HVAC equipment is which is level with the living space?

Tried to share an image but maybe this link will work: https://drive.google.com/file/d/1-BZGDF5Hpi6f7txCk4_660wvcbqo85Og/view?usp=sharing
 
#9 ·
Something to consider:

Before putting a return vent in the attic...
Do you have a condensing furnace with 2 pipe (2x PCV pipe for combustion air and venting burnt gases) venting???

If not... then do NOT put a return in the attic.
Supply yes, return NO!

Reason has to do with potentially sucking CO (carbon monoxide) into the system.
 
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Discussion starter · #19 ·
The reading is from the Ecobee thermostat that is in the living area on the 3rd floor of our home. However, now that the attic has been spray foamed, the attic has a similar air quality as the living space.
 
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