Roof pitch and overhang questions — among others…
With a latitude of 44 deg 11 min North, and a longitude of 72 deg 23 min West, can anyone tell me what the roof overhang should be on each side of an attempted passive solar home?–(a kit house I can sketch and order from Landmark Kits.) (There will be some kind of porch…along the west side? Haven’t figured out the pitch of that either.)
Also, what is a good pitch for potential future fixed solar panels and not having to shovel boatloads of snow? An 8/12?
How many degrees of true south should the home be positioned…and how do you find true south?
I am planning on a walkout basement — maybe radiant in the floor — with a wood stove in the cellar. Do you think it would be cheaper to put in a two-storey 20×30 home–3 stories with the basement, or a home with one storey plus the basement, maybe 30x50ft? Overall?
Are there any hardcore proponents of a slab and not a basement?
I am going to get a friend to put up the kit — they just come with the bare bones, and then we will have to finish it. Please — any ways I can save money? Not looking for fancy — just function. Please suggest.
Oh yeah — and for each of those building scenarios, if I go for the popular 7% for passive solar, what do you suggest for size (and type perhaps) of windows and placement?
Please don’t laugh 🙂 I’ll get this done with a little help 🙂 Thank you so much for any helpful suggestions! I appreciate it.
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Replies
J.,
That's a lot of questions for one post. I'll take a stab at some of them.
Q. "With a latitude of 44 deg 11 min North, and a longitude of 72 deg 23 min West, can anyone tell me what the roof overhang should be on each side of an attempted passive solar home?"
A. One of the best tools for this purpose is a free online tool from Sustainable by Design. Here is the link: Overhang Design.
Q. "What is a good pitch for potential future fixed solar panels and not having to shovel boatloads of snow? An 8/12?"
A. My latitude is about the same as yours, and I like a 12/12 pitch. My winter solar panel angle is steeper, however, and the snow doesn't slide off the panels. (For that, the panels need to be almost vertical during the winter. That means that you need to adjust the angle of the panels for summer efficiency.)
Q. "How many degrees of true south should the home be positioned...and how do you find true south?"
A. Orient your house as close to true south as your lot allows. You can find south with a compass or with a vertical stick. Mark the moving shadow of the vertical stick on a sunny day (you want to mark the point of the shadow corresponding to the top of the stick). At the end of the day, draw a line from the base of the stick to the mark that is closest to the base of the stick -- the mark indicating the shortest shadow. That like is your north-south line.
Q. "I am planning on a walkout basement -- maybe radiant in the floor -- with a wood stove in the cellar."
A. This is not recommended. Wood stoves installed in basements often have problems. For more information, see Why Is This Wood Stove Misbehaving?
Q. "Do you think it would be cheaper to put in a two-storey 20x30 home--3 stories with the basement, or a home with one storey plus the basement, maybe 30x50ft?"
A. It's time to sharpen your pencil and prepare a construction estimate.
Q. "Are there any hardcore proponents of a slab and not a basement?"
A. The answer depends partly on your site, and what you might do with your basement space.
To find true south using a compass, you need to add a correction factor because true south differs from magnetic south. Here in Maine, you need to add about 15 degrees to the compass reading. Thus, true south is about 195 degrees on the compass.
J. I'm going to suggest that you hire an architect, preferably one that is familiar with Passive House Planning Package and / or WUFI analysis. While those tools aren't guaranteed to give you completely accurate energy use results, in the hands of qualified and experienced professionals they are the best tools available to help guide your decision making process. I'm not saying you should necessarily aim for the Passive House standard, but that experience is invaluable in helping you make energy use decisions.
As for saving money the best advice I can give is watch the square footage, and make your decisions on the finishes as early as possible. Making finish decisions early allows you time to shop for deals. For example early on in my build process we decided to have stone counter tops in our bathrooms. By visiting several dealers we were able to find off cuts that fit our needs for a fraction of the price.
As for square footage a small home can live big, Sarah Susanka's book The Not So Big House has examples and ideas that can be used to help your house live larger than it actually is. An architect can also help you identify and prioritize what's important to you in your house.
Wintertime daily high temperatures make a huge difference in how clingy snow is to LCA (the plastic coating on most PV panels), and how steep it needs to be to shed snow in a reasonable amount of time. Anywhere that the average daily high in January is at or above freezing will shed snow just fine with an 8:12 pitch, but 6:12 could be marginal.
If the daily high during the snowy season is under 20F, forget about it- it needs to be a real lightning-splitter type of roof (how does 12:6 grab ya? :-) ) to reliably shed snow. At 12:12 it will eventually avalanche with the panel as the sliding surface, but it has to be enough snow-weight to break the bond. Seasonal weather patterns matter too- a light snow followed by a week long cold snap will make that thin layer weakly bonded, and it will avalanche sooner than if it stayed cold, or had a couple of mild (but not clearing ) thaws before subsequent snows. A 12:12: pitch is in the heart of the danger-angle zone known to backcountry skiers, since it can build fairly deep but unstable snowpacks readily triggered into avanche by the introduction of an unwary human. Below 6:12 it almost never slides naturally on rough surfaces, but can still glide slowly on LCA-clad PV panels during thaw cycles. At and 8:12 pitch it'll glide a lot faster than at 6:12, and may even avalanche abruptly during a sufficiently deep thaw.
My daily commute is roughly along the 42nd parallel, in a maritime region where the mean mid-winter high is just about at the freezing mark. I pass several PV arrays along the way- the one that's at about 4:12 takes a month or more to clear a foot of snow and is often covered for 8-10 weeks of the winter. Those in the 6:12 range clear in about a week, but at 8:12 plus it's only a matter of days, providing it's not during a cold snap. This one I estimate to be roughly 8:12, and it clears in under 3 days of daily highs breaking 32F (by even a tiny bit.): http://goo.gl/maps/21ZtY
Just looked up your longitude/latitude- the weather on Smith Rd. in Orange VT isn't favorable to shedding snow quickly on an 8:12 roof, with normal daily mid winter highs only in the mid-20s.
http://weatherspark.com/#!dashboard;a=VT/Orange