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Passive solar orientation

TIBBALS | Posted in Green Building Techniques on

I have acquired a lot with amazing views to the north…for miles and miles. Of course I would want my living area on that side because of the view. But, I want to build a passive solar ICF home and most of my windows should be on south. I thought about clerestory windows on the south but I know that will not be enough.

Great feedback already, WOW! I live in North Alabama where we have pretty sunny winters that can be surprisingly cold without beautiful snow. The humid summers with sweltering heat can start as early as May thru October with temps in high 80’s and low 90’s.

My home will be 1800 feet with 800 feet walkout basement and 1000 feet above ground and then a garage above ground as well. We have one passive house built recently in the news. Due to the slope of the lot, my garage has to be on the South side. Should I just abandon the view and purchase a south facing lot or perhaps just built a tight envelope with Geothermal HVAC and/or solar, great insulation, and very good windows. This is my retirement home and being handicapped, I want a lot maintenance, energy responsible home.

Thanks for the practical and intelligent responses. Hope the added info helps paint a more accurate picture of my dilemma.

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  1. GBA Editor
    Martin Holladay | | #1

    Q. "Any suggestions on what I can do?"

    A. My advice is to start by reading this article: "Reassessing Passive Solar Design Principles."

  2. rockies63 | | #2

    A lot depends on the size of the house you want to build. If you are primarily concerned about light then creating a roof that has clerestories along the south side of the house is probably enough to get sunlight into the main rooms. If you also want the house heated by the sun then perhaps you could make the house one room wide and have windows on both sides of the rooms.

    If you want a wider house you could have all the main rooms on the north side and add a wide sunspace along the south side of the house and use air vents in the wall dividing the rooms for air circulation.

  3. tommay | | #3

    Perhaps some type of solarium, maximizing and storing heat gain to compensate for the loss on the north side. Insulated curtains or inserts can also be incorporated on north side to minimize heat loss when your not looking.
    What type of home? Rural? Wood stove or mass heater? Solar hot air/ hot water heater?

  4. Expert Member
    Michael Maines | | #4

    Reconsider building your home from ICFs, for one. For some reason people who build them think they do things that other houses don't, but it has become relatively easy to build airtight homes, better-insulated than ICF homes, that can withstand natural disasters just as well, with an enormously lower carbon footprint than ICFs--particularly their concrete core.

    From a performance point of view, most ICF homes have walls around R-21, code minimum in cold climates, and weak at that--with almost any other system, through energy modeling I can show a decent return on investment to use higher levels of insulation. The best ICFs are about R-30, but few people choose them due to their extra expense, which is high relative to increasing R-value with other wall systems. It's true that their is some benefit to the thermal mass of concrete, but in most cases it's much less than what people imagine.

  5. Robert Opaluch | | #5

    You didn't mention your climate or proposed home size. You need to know if your climate is appropriate for passive solar. Namely, cold AND SUNNY winters. If you have overcast winters, solar heating won't work. I assume that you already know that you have good south-facing solar access. The mid-winter sun is low on the horizon in December and January, so most of your south-facing windows can't be shaded by adjacent buildings, trees, hills, etc. Wintertime direct gain solar heating won't work if direct sunlight is blocked from 9 or 10 AM thru 2 or 3PM.

    For a lot more useful details on solar gain, please see:

    Since your views are to the north, you likely have longer north-facing and south-facing walls (and shorter east and west). That means you likely will have more south-facing and north-facing window glazing, and less east- and west-facing. Typically that's good for wintertime solar heat gains (south) and minimal summertime solar overheating (north). You don't mention the size of your house, but as Scott mentioned, you may have rooms that reach both north and south sides of the house. For true passive solar heating, you need (1) a super insulated, airtight envelope to reduce the winter heating load; (2) enough south-facing glazing to boost wintertime solar gains to reach your wintertime heating needs (but not overgrazed like many early poorly engineered solar home experiments); and (3) enough thermal mass to absorb solar heat during winter afternoons, and radiate heat back into the room overnight). A polished 4" concrete slab floor (or tiled slab) works fine and doesn't add to construction costs, as you have to budget some finish flooring anyway. Finding windows in the USA with a good solar heat gain coefficient (SHGC = 0.5 or 0.7 range) is not easy.

    You must be able to calculate your heat losses and gains to size the south-facing glazing. Or, just use a modest amount of south-facing glazing, skip the thermal mass, and benefit from a "solar tempered" home that's solar heated during sunny mid-winter days, but needs auxiliary heating by the early AM during the winter.

    The added benefit is that during those dark winter months, your home will be brighter from solar heat gain during the day. North-facing windows get very little direct sunlight all year round. West and east windows get some morning and afternoon sunlight during winters, but can be brutal with unwanted solar gains during the summer. Best to reduce the number and size of west windows (and east) to increase the number and size of north (views) and south (light and winter heat), without overdoing it.

    Hope this helps. The article goes into a lot more detail. Best of luck designing and building your own home, a great adventure!

  6. Expert Member
    Akos | | #6

    I had somewhat similar issues, because of firewall requirements in the code, I couldn't put any south facing windows in the walls. Ended up with about 100sqft of clerestory windows over 1100 sqft of floor. It does work great in the winter time, during sunny days the heat does not run. The ratio is a bit on the high side, sometimes the house does get to around 26degC which is a bit too hot (but you can always open windows a bit, so not a big deal).

    Items to watch for:
    -get the overhang correct. I went by the passive solar recommendations and there is too much solar gain in September. I would recommend aiming more for mid/late October for sizing the overhang.
    -passive solar and high mass heating are not your friend. Once the sun goes down, it takes a bit of time for the heat to come up and there is always a slight dip in the temperature in the evenings.
    -the sun from the clerestory will be shining into the house during the winter. Consider where this hot spot will be and how it will move as the sun changes. I have about 2 weeks in which I can't standing behind my kitchen island around 4pm because the sun in my eyes.

    Overall, getting too focused on solar gain is not worth the effort. You can create a comfortable energy efficient home with having to deal with it.

  7. rockies63 | | #7

    Martin, in the article you link to in comment #1 you mention: "Some designers (including Joe Lstiburek) have abandoned the idea of orientation-specific glazing specifications and now advise that all windows should have a low SHGC."

    The next sentence says: "Don't do it."

    "Don't do it" may mean "do not choose orientation specific glazing" or it may not.

    Are you agreeing with Mr. Lstiburek's opinion that all windows should be low SHGC, or are you saying to ignore his advice and continue to choose windows designed for specific orientations in the building?

    1. GBA Editor
      Martin Holladay | | #8

      The sentence you quoted -- "Some designers (including Joe Lstiburek) have abandoned the idea of orientation-specific glazing specifications and now advise that all windows should have a low SHGC." -- was the last paragraph of a section. I did not comment on Joe's advice. For many homes, it's valid advice.

      The words "Don't do it" are in bold; that's a heading (a type of headline) introducing the next section. The heading summarizes Joe's advice in the paragraphs below the heading, where he advises, “Don’t bother with the passive solar."

      My advice differs somewhat from Joe's. My advice can be found at the end of the article, in the section under the heading, "A new look at the old principles."

  8. thrifttrust | | #9

    The Lstiburek comment, “I don’t think orientation matters anymore,” and the reasoning behind this view is comfort for me. I don't like direct sunlight entering my home. I'm reminded of this as I'm blinded by the kitchen window when I make my wakeup coffee. Besides being an inefficient and erratic means of climate control, It's a terrible source of light.

    Indirect skylight is much better for lighting, yes it's even, but even more, it's penetrating. This is due to the inverse square law. It means that as you move away from a light's source it's intensity falls off dramatically. Most of the light provide from direct sunlight doesn't come from the sun, It comes from the walls, floors, furniture and window treatments the light falls on. The room ends up with a bright side and a dim side. Indirect skylight comes from scattered sunlight emanating far over head. As it travels the last few feet across your room it suffers no appreciable dimming. The space is filled with even light.

    Windows aren't furnaces, their job is to illuminate, to see out of, and as Joe says, "Every once in a while some crazy person wants to open the damn thing." Capture your north views Tibbals, and joy in the light the windows provide. Another thing about views, the first thing you learn in photography, have the light behind you.

    I'v learned so much from Joe Lstiburek, For me his most enduring message is, don't let efficiency stand in the way of beauty. His reasoning is that no matter how efficient and well made a house is, If it doesn't embody beauty no one will take care of it.

    Douglas Higden

  9. brad_rh | | #10

    I just have to say a few things since there's so much anti-sun sentiment here. I live in a sun tempered house in a cold, sunny region & we love the bright sun in our great room. Typical Jan day here is low of 15, high of 40 and sunny. The heat runs for a couple of hours in the morning (5-8Am). We don't have an overheating problem that can't be handled with a ceiling fan. We have a wood floor, not tile or concrete. The house is not super insulated, just 'pretty good'. In a heating climate high SHCG windows on the south side itsthe way to go. They're not as hard to find as they were 10 yrs ago.
    I don't know about northern alabama, as someone else commented, make sure you have plenty of overhang over those windows.
    I've read several of Joe L's articles, and I know he's a smart guy, but he's wrong sometimes.

    1. tommay | | #11

      Yup, sat in front of a sunny window this morning for some time. Sun still coming in. Haven't used my boiler in the last few years. There used to be neighbors trees blocking all the sun. Now I just turn it on once and a while for a few minutes to make sure it still works. Unfortunately, they limit our sun time these days, so you gotta make the most of it.

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