Some might take a look at our building choices (light metal roof, super efficient windows, super efficient HVAC, spray foam) and think we've gone "green". The thing is, I don't believe in fashionable environmentalism. I just don't. Talking "Green" makes me green, if you know what I mean. That doesn't mean that I don't care. I've been an outdoorsman for my entire life. I firmly believe in responsible stewardship of our land, air, and water. I even more firmly believe in EFFICIENCY that is consistent with such. Economic reality should dovetail into environmentalism. If it doesn't then it's just a fashionable bit of onanism. I'm not sure most folks get that.
Anyway, environmentalism should make sense. You have to look both short and long term at both costs and benefits.
Short term and long term costs for our metal roof were a no-brainer. It won on the upfront without even considering that it would outlive us, let alone the cooling costs. Windows were a no-brainer because added efficiency could be had at trivial additional cost, and no matter how we sliced it, we had to replace the windows (the calculus becomes much more difficult when one has a passel of solid old windows and the time to work on them, as well-repaired old windows with interior storms can be pretty darned efficient).
I did have to do the up-front vs. monthly/lifetime cost calculation when I was figuring the costs of insulation. I figured that we could DIY bats or blown-in insulation if we framed in all of my brick walls. This would preclude insulating the stairwell wall, of course, because we couldn't give up that space without rebuilding the stairs. The cost of that is ~100 square feet of floor space (and elbow room), and probably $2500 in materials, perhaps quite a bit more. Plus our time, which was short. The efficacy of 3.5" of bat insulation against the brick walls is debatable (some say R-11), but it's got problems in our application. The stair wells are going to be major heat sinks, for one and that means that the office and living room would be cold. Further, if insulation gets moist or if there's a gap allowing air to get in there, the true R-value drops significantly. There's a chance of both in our old brick house. I've seen a lot of water find a way into our walls over the past year. It could happen again on smaller scale. So, we're not going to be able to make the place fully insulated with pink stuff regardless, and if we did, there's a good chance we'd get less than the hoped for result.
Now, a lot of folks in these 150 year old houses don't insulate the walls, and just leave them plaster on brick with an air gap and more brick. They save the floor space in these narrow homes at the expense of comfort and gas and electric. With good attic insulation and storms and plastic it's bearable and almost affordable.
If we did spray foam, we'd get far superior performance for the life of the home (never any settling, never get wet, never allow a draft through, and provide R7 per inch (that's R-11 on the walls) AND eliminate the need for venting in the attic), and save ~100 square feet of needed floor space/elbow room. Most importantly, we could insulate the stair wells, making a huge comfort difference. I figured that I could fur the walls out 1.5" and get "real world" equivalence of bats in between studs without ever having to worry about the normal failure of bats in our application. In the rafters of the attic living space, I'm confident that the 7-8" of foam that we sprayed is going to outperform any other insulation. Forever.
Now, the total cost of the foam was less than $6k and we didn't have to do any of the labor nor take any of the risks (foam is fairly expensive if you screw up the application). That's perhaps $1.5k more than DIY foam (assuming no screw-ups), $2.5k more than DIY bats and $4.5k more than leaving the walls and just insulating the attic. I know that I'll save at LEAST $100 per month over the no wall insulation application and probably $50/month over the bat solution. Plus I'll keep that elbow room. We'll also get into the house sooner, saving on rent.
I figure that the cost differential alone is conservatively made up in less (perhaps a lot less) than 5 years, assuming utility rates stay where they are. That's a pretty short pay back and it makes good sense when I get to wait for it in total comfort. By comfort, I do mean serious comfort. In real life, when we set the furnace at 60 degrees, it's about as comfortable as our current place set at 70 degrees. When we turn it down, the third floor stays toasty for hours and hours. That's the outcome I was looking for and the savings justify the cost, irrespective of the luxurious comfort.