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Extremely High Attic Temperatures

user-621079 | Posted in GBA Pro Help on

Recent client of a BP installer has a complaint that her “attic temps are well over 100F” in Summertime after spray foaming roof deck 3 yrs ago.

Very typical 22 x 38 attic layout, 9 or 10 pitch roof over a 150 y/o 2 story gable end New Englander. The typical old New England house. Southern New Hampshire location.

Attic space is intended to be a fully insulated space but is not purposely conditioned w/ heat or cooling.  No venting.

5-6″ closed cell spray foam, on roof deck, 3-4″ on gable triangles.

The previous gable end attic vents were spray foamed over.
1 masonry chimney through the attic and roof but it doesn’t run in Summer, is just a space heating boiler, DHW is electric.
No gable end glazing nor Skylights.
Not much shade on the roof, it’s Summer.

I think the summertime attic temps s/b within about 15F, give or take, of the 2nd floor rooms.

We just visited for the 1st time to take a look, but it’s April, ext. temps were 55F, the 2nd floor bedroom and hall temps about 70F and 5 points measured in the attic were all about 71F. All seemed fine at the visit. Client insists it is impossible to enter during Summer and she is wary is storage up there.
We’ll be returning 1st of June to see what sunnier days and higher ext. temps may do.

1) Am I right expecting the attic space should be pretty close to the 2nd floor space and 2) if it truly is over 100F in the attic, any suggestions about the likely causes?

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  1. [email protected] | | #1

    I would expect temperatures to be about 10-30 degrees higher. AcuRite makes some low cost sensors that I use to monitor temperature and humidity in the attic (which has 2-inches of closed cell foam against a site-built air vent). You may want to add a 10-20 CFM if they are storing anything of value up there.

  2. Expert Member
    Akos | | #2

    Without any cooling the attic temperature will be a ratio between the roof insulation and the ceiling insulation plus you'll get a fair bit of stratification because of the height. This generally means the attic will be hotter than the dark lord's nether region in the summer. Not as hot as an uninsulated attic but still hot by human standards.

    This doesn't mean the insulation is not working a small amount of airflow from the house should make a big difference (50cfm/1000sqft of floor space). Along with a small supply a return near the peak would make the biggest difference.

    If this doesn't fix the heat issues, there could be some large air leak still in the attic. Sometimes the spray foam installer can't get into the soffit area and a big opening could have been left.

  3. walta100 | | #3

    The way I see it your client was sold a “free lunch” and is now surprised that it is not happening.

    Given how hot the attic is it seems they almost certainly left the old insulation on the attic floor and the R value of the old insulation on the attic floor is higher than what was applied the roof.

    If you can get the client to call it a “conditioned attic” you may be able to convince them spend the money required to buy and operate the equipment necessary to heat and cool the attic to more or less the same temp as the rest of the house.

    Seems to me if a hot attic is the biggest complaint, they should count that as a win in the game of Russian roulette they are playing the big risk is mold and rot. It seems inevitable from time to time the surfaces of the attic envelope will become cooler than the dew point of the unconditioned air in the attic. When it does water will condense on the surface. The really question becomes how much water how often and will it evaporate before mold and rot get going.


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