Quote:
Originally Posted by CorsiHockeyLeague
Second thing - I asked for pricing to do 3" exterior insulation around the whole building. Cost is a little over $5000. Now, this isn't a region where it gets super cold a lot of the time, but given the number of windows and everything, that seems reasonable. Thoughts of others on whether I pull the trigger on that? I am getting a little nervous with the way the costs for this thing are increasing.
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I wouldn't do it. The payback period for going much above code in the west coast climate if you're heating with a heat pump is usually ridiculously long.
Just as a point of reference, my house costs $400-450 a year to heat and cool in the same climate with heat pumps. And that's a 2,000 square foot house with a mix of 40 year old and 20 year old windows, 2x4 walls, and a mostly original envelope (I bumped up the attic insulation and did a bit of air sealing). So by any measure, your place should use a fair bit less energy to heat given that it's smaller and newer. But even if it didn't, the payback period would be crazy.
In general, about 20% of heat loss in a house is through walls, but in a modern building with decent wall insulation and a lot of windows, it can be even less. And because R-value is linear, you start to hit diminishing returns by adding more insulation to an already decent wall [see chart below in spoiler tags]. With 2x6 walls, you'd probably be reducing the heat loss by 40% or so by adding 3" of insulation outside. But that's only 40% of the wall loss, so it'd be more like 8% on the whole building (assuming the 20% figure above). So using the figure for my house above, you'd be saving $30-35 a year with the 3" of extra insulation, which is a 150 or so year payback.
Granted, some energy upgrades will improve the comfort, so it's not a strict payback calculation. But I'm not sure exterior wall insulation will really do that to a well built modern home. The windows are going to be the weak point of the envelope in terms of heat loss and feeling colder if you're near them, and the insulation does nothing for that. With proper air sealing (which basically any modern house has), there isn't going to be enough heat loss through walls to impact comfort with or without the exterior insulation.
