The Lambertville house needs literally everything. One of those needs is insulation. With demo done, we have a house down to the studs that is, more-or-less, an open slate. Putting it back together is an interesting and challenging exercise in design, both functional and aesthetic. Behind our old plaster and drywall walls were old balloon framing and some old-school insulation: bricks, straw, some fiberglass batt insulation from a previous owner’s partial renovation, a baseball card and a bra.
Now that the bricks are stacked outside for a currently unknown future use (any ideas?), the baseball card (Ed Charles’ rookie) valued at $3.25, and first estimates gathered for insulation options, the evaluation of insulation options can begin. Among those options are: closed cell soy-based spray foam, open cell soy-based spray foam, and eco-touch (or similar non-toxic batt insulation. For budget reasons we could do a combination of two options, too (closed cell on the ceiling / open cell on the walls, closed cell on the ceiling, batt on the walls; etc.).
I know a little about this stuff, but to better understand the options I am working with a mechanical engineer, Joe (I met Joe through the @digsau softball team a few years ago). To better evaluate HVAC options, insulation, and windows, Joe modeled energy performance with a variety of combinations of insulation, windows, and HVAC systems.
While there is a good deal to evaluate - everything from R-values to cost to toxicity - the following chart from Joe’s report summarizes the various r-value qualities of some of the options:
Because r-value is measured by inch of insulation, the depth of a wall or rafter has a large impact on the overall r-value of the section. In our house, filling the roof rafters with closed cell would result in a total r-value of around 48. Compared to the r-19 gained by using typical batt insulation, that is a significant difference. In the walls, using closed cell will result in R-19, where open cell would lead to R-11 and batt insulation R-7.5. From a sheer r-value perspective, closed cell is the best option. It also is inhabitable to mold and bacteria and adds structural strength to the house.
On the surface, this is a great solution. Digging a little deeper though, how much does it matter? Joe further quantified the differences here:
The thing that jumps out at me, and that I’m following up with Joe on, is that I am surprised that the roof insulation upgrade does not result in a more tangible improvement. I am not yet sure why this is. Obviously heat rises, and my assumption has always been that improvements to the ceiling r-values have a big bang for your buck. In this case, that does not seem to be so clear. There is significantly more wall volume than roof, so my thinking is that must be what drives it, but I’m just not sure yet. Overall, spending the additional money on all options would result in operating costs of +/-$1,200 / yr. compared to about $2,000 annually with the base case assumptions, according to the model. While I don’t know yet how much we’re talking about, there is also an environmental benefit in reduced carbon emissions from lower loads in the heating and cooling system.
So, what is the true cost/benefit of the upgrades? At this point I have incomplete estimates for various aspects of the base case vs. the upgrade options that were modeled. In reality I may never know exactly, and I am okay with that. The goal isn’t to split every hair, but to make a good decision based on tangible evidence, and not just what salesmen suggest or whatever is in sale at the supplier.
That said, I know enough from previous projects and from the estimates I do have for various upgrade options to have a sense. Assuming you were to do every option detailed, and that you did, in fact, save $800 per year, what is that actually worth?
Using some rough numbers and admittedly incomplete analysis, if you wanted a 5% per year return on your capital improvement investment, the improvements would need to cost $16,000 more than a base case scenario (you have to spend something - the house needs all new systems). The systems in question are insulation, HVAC, and windows. I do think the upgrades would cost around $16,000 more than the base scenario, and that the return, roughly speaking, is 5%. If you were to invest $16,000 and get a 5% return that would commonly be pretty acceptable, especially now, but what about in this case? When the time comes to sell the home, can we get that money back? Would someone pay more for the savings compared to other homes that they could buy? Some people will, for sure; but many will never care.
Though this exercise isn’t just about money (I knew coming in that closed cell insulation and better windows would cost more), it is, obviously, a factor. As with everything in this process, there is a constant give-and-take between function, budget, and aesthetics. The answers aren’t always obvious, but I am committed to making decisions, and not just following the crowd in development.
