Does a Black exterior home actually increase cooling costs?
jayhawkcrna
| Posted in Energy, Heating & Insulation on
We are in process of designing our custom home. We would really like to paint the home Black with cedar accents. We are in NE Kansas, Climate zone 4, so we have both heating and cooling needs. I know dark paints will absorb heat more than lighter colors but if the home is insulated will we actually notice a huge difference?
Replies
I would expect it to do so. It also increases heat loss in the winter and will nudge heating costs up.
If you will notice this, will depend on how close you are looking.
https://www.nrel.gov/docs/legosti/old/15771.pdf
That could have a positive impact on heating costs during the cold seasons, especially if they last longer than warm seasons. Homeowners may also avoid choosing black, navy blue or other dark colors because they're known to fade with sun exposure.
I am responding as an engineer that has special training in thermodynamics. Dark colors absorb heat and also expel heat to the environment or surroundings. That is why the air cooled VW engine tin surrounds were painted black. What is more important for a home and the exterior surfaces is the ability of the outside surface of the home to absorb and hold the heat or not hold the heat. Brick or masonry is a material that will hold onto the heat and will pass it into the walls of the home. It will take the entire day to do so and the heat will be a problem for cooling in the warmer months of the year. In the winter it will be beneficial.
I live in a hot humid area of the country and I am planning to reside my house. I am going to use white painted metal (steel) siding with a 3/4 inch air gap between the sheathing surface and the siding. No siding material will be water tight. So the air gap is to allow drying. Why metal siding? Because metal has interesting properties. It absorbs heat well from the sun, but since it is thin it also allows the heat to easily escape into the air gap and to the surrounding air. After the sun goes down that steel siding will loose the heat very quickly and it will not be stored like it is in masonry so the cooling system will not have to deal with it when I am sleeping. The layer under the siding will have 3/4 inch thick furring strips on 3 inches of polyisocyanurate rigid board insulation; 2 layers of 1.5 inch with taped and offset seams. Under that will be a drainage layer about 3/8 inch thick and then a minimum of 1/2" CDX plywood. No water resistant barrier because I want the interior water vapor to be able to escape if it is condensing. It will escape through the plywood and in the drainage layer and come out the bottom of the insulation layer to a metal flashing that meets the exterior siding.
The R value of the final wall will be about R-33. The wall insulation is 15 but the 2X4 studs allow some thermal bridging so the final R value for the stud wall is about 12. The three inches of polyiso with taped seams will give about an R-21. So 12 and 21 is 33. More than is required by any code in the future in Zone 2.
You could do something like this and simply use black metal siding with hidden attachments. Bridger Steel is one source that has what you need. Nickel gap siding would look neat.