South or southeast orientation in Southwest U.S.?
I will be building a 20×40 rectangular house on a slab on grade with a painted concrete floor. It will have a gable roof and 2′ overhangs all around and minimal windows on all but the south side. It will be located in Arizona, in the slightly cooler part of Climate Zone 2B, where typical winter days range from 28 at night to 55 in the afternoon and summer days range from 60 at night to 100 in the afternoon Is the ideal orientation for the long side of the house to face due south, or should it face somewhat southeast so that it warms faster in the morning sun and catches less sun in the afternoon? If the latter, how would the ideal southeast angle be determined?
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Replies
Jeff,
I vote for due south. It simplifies overhang design.
I doubt whether the purported advantages of wintertime solar heat gain through east-facing windows outweigh the clear disadvantages of summertime heat gain through those same windows. I would minimize the size of east-facing windows if I were you.
For more information on this topic, see Hot-Climate Design.
Porch on the west side for west side window shading. Bedroom on the east side wake to sunshine. Bathrooms on the northside, dining room shaded by the west porch. Insulate the ceiling well, use foil backed plywood for the roof sheathing.
Another vote for due south, with the roof lines optimized for photovoltaic solar. Even if it's not cost-effective to install the solar now, it will be well before the shingles are toast (and it might be cost effective now, with or without subsidy incentives and tax credits- it depends upon your utility rates.) By 2025 the lifecycle cost of rooftop solar power will be cheaper than the residential retail rates almost everywhere in the US, and may be below the wholesale grid rate for large parts of the US. With any new construction it's useful to keep this in mind, and not design, shade or site-orient yourself out of being able to take advantage of cheap PV.
Martin is right about minimizing east & west facing glass. East facing windows proved to be the only comfort problem on a high-R house project I was involved with a couple years ago in climate zone 5A, roasting the occupants out of their east side bedroom on sunny July mornings. (There wasn't even that much window area!) If you have any significant east or west facing glass you may need exterior shades to kill unwanted seasonal gains, since it takes a deep porch to reduce it with mere overhangs. as AJ suggests.
Do you think SE orientation would still be a dealbreaker in the PNW / climate zone 4C?
Thank you. The house will have just two very small windows on the east and west sides. The difference between facing due south and somewhat southeast will be felt in how much sun the bigger south-facing windows get in the cooler morning versus the hotter afternoon.
According to the very handy tool at susdesign.com, if the house faces due south, my 2' overhang will barely shade the bigger windows on the south side at any time of day on 1/22, 11/22, and 12/22. It will shade around 25% of them on 2/22 and 10/22, 60% on 3/22 and 9/22, and 100% April through August. March here isn't hot, but September is.