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Given that hot air rises, it's easy to understand how attic insulation can help keep a building warm; say, in the winter, for example. But when winter changes to summer, does the attic insulation help keep the building cool? Or even worse, does attic/roof insulation make the building hotter by resisting the flow of heat up and out?

In the below diagram, my idea is that the R-factor of the attic insulation will resist the flow of heat up and out of the building by impeding flow from zone 1 to zone 2 in the below diagram.

Figure 1. Premise: R-factor resists heat flow from zone 1 to zone 2 thus trapping warm air inside the house in the summertime?

enter image description here

How would we quantify the overall effect on house temperature based on this and other competing effects? Both theoretically and empirically?

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    $\begingroup$ This highlights the understanding of the old joke about the thermos flask : when you put hot things in they stay hot, when you put cold things in they stay cold - how does it know? Apply nationality as necessary (not mentioned to be pc).... $\endgroup$
    – Solar Mike
    Nov 20, 2017 at 7:13

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Attics are much hotter than the outside air when the sun is shining on them (say 120F in an attic). When the air conditioning system is running the internal air temperature is less than the outside (lets say 72F in the house and 85F outside). The ceiling temerature might be warmer than the floor, but both will be much cooler than the attic (say 73F for the ceiling and 71F for the floor). Heat will transfer from the hotter attic (120F) into the house (73F ceiling temp), so ceiling insulation is very important for keeping a house cool.

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  • $\begingroup$ I understand your thought process. But don't you agree there is at least a second order effect that counteracts the cooling effect you described? Specifically, the effect as described by the diagram in the OP? How would we quantify the overall effect on house temperature based on these two effects? Both theoretically and empirically? $\endgroup$
    – Mowzer
    Nov 20, 2017 at 6:26
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    $\begingroup$ The image is a special case or an incorrect dramatization. Heat transfers from hot to cold. There are no hidden effects. If the inside of the building is colder than the attic, heat will transfer into the building. Period. The rate will be deturmined by the temperature difference and amount of insulation. $\endgroup$
    – ericnutsch
    Nov 20, 2017 at 6:36
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in the summer, the outside of the house- especially its roof- is hotter than the inside of the house. In this case, attic insulation does not physically "cool" the house- it just impedes heat transfer from the attic to the inside of the house.

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  • $\begingroup$ But won't the resistance to heat flow provided by the insulation keep the warm air inside the living area of the house? Instead of letting it rise to the attic? And then to the outside? $\endgroup$
    – Mowzer
    Nov 20, 2017 at 5:48
  • $\begingroup$ See edit and diagram. $\endgroup$
    – Mowzer
    Nov 20, 2017 at 6:13
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    $\begingroup$ still agree with ericnutsch. $\endgroup$
    – niels nielsen
    Nov 20, 2017 at 19:20

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