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Attic Venting/Winter

Attic venting/Winter/

... last week, the night outdoor temperature was about - 18C/-1F
Daytime temp. was about - 8C/17F

What air temp. should I expect in my attic?

a) close the same?
b) 20% warmer?
c) 40% warmer?

Asked by Hans Mayer
Posted Tue, 02/18/2014 - 17:08


2 Answers

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There is no single answer to your question. (By the way, you can't talk about a percentage increase in a temperature unless you are using the Kelvin scale, which starts at absolute zero; otherwise percentages are meaningless.)

Attic temperatures in winter will always be warmer than the outdoor temperature and colder than the temperature in the indoor space. The closer it is to outdoor temperature, the more effective the insulation layer.

Among the factors that will raise the attic temperature are the following:

  • Sunshine on the roofing
  • Air leaks through the ceiling
  • Conductive heat loss through the insulation on the attic floor
  • Leaks in duct seams located in the attic

Attic ventilation tends to lower attic temperatures in the winter, but will never lower the attic temperature to the same level as the outdoors.

Answered by Martin Holladay, GBA Advisor
Posted Tue, 02/18/2014 - 18:21

Helpful? 0

Don't forget the radiant losses to the night sky on a clear night, which can bring the roof surface temp down to the dew point of the outdoor air, which will often 5-10C colder than the outdoor ambient temperature on clear cold nights with very dry air.

And how about wind-speed & direction (relative to your roof venting & shape)?

There's no simple model- assume that the attic CAN get down to the outdoor air temp under some sets of conditions, but don't presume that it always will.

Answered by Dana Dorsett
Posted Tue, 02/18/2014 - 18:41

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