Practical impact of varying rectangular building shapes
Hello. I am a keen reader of the GBA site and even more so as we have recently purchased land to build and are saving to build our own house in the next couple of years. From this site and others similar, I have some understandings of large concepts and how they play out in the building process, but with no experience building, it is all largely academic. I do have a question though that I have been considering for a while (as someone dreaming to build in Northern Michigan, zone-6).
I understand that there is an impact from the building’s shape on energy efficiency and that there are a number of factors that affect this. A dome is probably the most energy-efficient (all insulation factors being the same) shape for retaining heat. Hexagonal shapes next, then an even square shape, as they are the decreasing ratios for surface area vs. volume. Further, I understand that there is a balance to be struck between solar gain and heat retention, meaning that a rectangular shape, if done well, may give a net gain for heat. I’ve seen it suggested that 2:1 (length:width) may be the most appropriate rectangular shape
for a cold-weather house that is taking advantage of solar gain.
There are many factors that go into such a thing and I understand many of these things technically, but my question is more about what it might mean practically.
Aesthetically, I love a long, narrow house shape, like a Scottish longhouse (maybe 2.5:1 or even 3:1). I don’t want to place all of my house design decisions on the math, as there are lifestyle considerations, but I also know that there are very real environmental conditions to be dealt with in the zone-6 climate and I don’t want to pay ridiculous amounts to live in a narrow house.
The question is: would a simple rectangular longhouse plan (3:1, length:width), air-tight and insulated to say r-40 walls and r-70 roof, appropriate glazing, etc. cost a lot more to keep than a comparable 2:1 house? I know that the math would give various percentages for the area-to-volume ratio, but I’m not sure how it translates practically.
Is 3:1 rectangular shape in a well-built house a huge deal or not that big a deal for my winter heating costs. I suppose I’m looking for “Pshht, it’s really not a big deal at all practically” or “Pshht, you’d be crazy to build a house with those dimensions in zone-6… you’d be throwing money away” sorts of responses ^^
This is relevant as we are talking about style things for building a house someday, but it is also just something that I have wondered for a while now, having read many builder discussions about house shape things.
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