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Passive solar orientation and shade-free zone

Randy Bunney | Posted in Energy Efficiency and Durability on

Friends,

I am writing to double-check my thinking on our passive solar building orientation and a shade free zone.

Next week a surveyor will stake out the building layout for our 1,100 sq foot passive solar home at 46 degrees N in Minnesota.

The structure’s southerly, solar-gain wall will be oriented at 210 degrees (30 degrees W of true south). Solar studies I have done show that we will get good sun light penetration into the structure during the winter with this orientation.

My understanding of effective passive solar building orientation is to maintain a zone free of trees or other obstructions so as to prevent shading 45 degrees or more east and west of the south elevation.

Question: Does the shade free zone rotate with the building or does the 45 degrees either side of south elevation remain fixed with orientation of true south at 180 degrees?

See attachment. I have outlined in red an estimated 45 degree obstruction-free zone that rotates with the cabin. Yellow highlights cabin orientation and true south.

I am probably over thinking this. Yet it seems to me that at some point the westerly rotation of the building away from true south the structure would no longer warrant a symmetrical 45 degrees clear zone east AND west of the south elevation

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Replies

  1. GBA Editor
    Martin Holladay | | #1

    Randy,
    By orienting you house the way you plan, the rooms on the south side of the house will miss some of the morning sun they might otherwise receive, but will get extra sun in the afternoon.

    In general, the answer to your question is that you should rotate your "chainsaw zone" to the east, so that the center of the chainsaw zone is facing south. However, I would be cautious here. You have to use common sense. I wouldn't implement a razed earth policy just yet. Cut down fewer trees that the rule implies, especially to the east, and live in the house a while. You can always pull the cord on your chainsaw later if you want to cut down more trees. Think about privacy and your views -- not just a rule you read in a book.

  2. Randy Bunney | | #2

    Practical and sage advice, Martin. Thank you.

  3. Steve Vigoren | | #3

    My home will be at 48.6 degrees in Northern Minnesota, and I will be oriented about the same as Randy, except towards the east instead of west. I am not calling mine a passive solar house, but certainly expect to get some help from the sun. So I will monitor it through the first winter to see how it goes. My lot slopes down to the lake from the home site, so that will help with the winter sun getting to my windows above the trees, I think. The trees are sparsely spread out oak, and I doubt I will cut any of them.

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