What percentage of a buildings solar heat gain is due to the roof, and what percentage is due to the walls?

Question

I am trying to determine the cost-benefit of adding more insulation to a roof versus using a different type of wall system.

This would be for a standard warehouse. Dark roof, concrete walls. Approximately 3 times as much roof area as wall. I am concerned mainly with cooling in the summer. (ie sun is high in the sky) Latitude 29 degrees, 30 minutes.

Answer 1

You are essentially asking a standard heat loss/gain calculation. Beyond the location of the building you also need to account for exposure, fenestration, etc. Additionally you need to be aware of what is in the warehouse. In that we (people) reside in the bottom 8' that would be the area of concern for comfort cooling and space conditioning for people. If you are storing perishable products you will need to account and address those items. A good point of reference would be the ASHRAE handbooks that most HVAC engineers have. In those you will find a wealth of information.

Answer 2

It would depend on your latitude ( the angle of the sun) and the reflective properties of the roof and walls. That would be a pretty straight forward calculation. Also shade trees help a lot. In most latitudes above 40 degrees, the walls would get the heat, if there where no other buildings or other objects to provide shade.

Answer 3

Used to work as a roofer and sider. We would take a thermometer on the roof with us. On a 90 degree day the temperature on the roof would be about 125 degrees. While a thermometer on the side of you house reads outside temp. so I would say probably 75% or more from roof generally. Many factors to consider though.

Answer 4

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Answer 5

Since many building departments specify R19 walls and R38 ceiling it seems they think the roof is twice as important.

Answer 6

It would also depend on the relative size of the walls and the roof.