Evaluating claims of spray foam efficiency and diminishing returns.
Leaving aside issues of thermal bridging and external continuous insulation being superior, how does one address the claims of spray foam installers regarding the diminishing returns?
For example you can find the claims (attached) that at at about 2 inches of closed cell foam you are getting 86% efficacy and by 4 inches you are at 92%.
Yet I can see people here like Martin Holladay make the point that R-value is R-value and double the amount will insulate twice as well. https://www.greenbuildingadvisor.com/green-basics/spray-foam-insulation-open-and-closed-cell#comment-39743
Are these tests wrong? Are they simply misleading? What is the disconnect here?
Climate 7A for reference.
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I'll be interested to read people's responses to this as well. I'd like to see it with reference to the table but with one small change. Instead of the left column referring to inches of spray foam, I'd like to see it in simple terms of R-value. So if spray foam has an R-value of 7 per inch we would start with a hypothetical wall of R-0. We would add R-7 to that. What's the reduction in the rate of heat loss? And if the wall is R-14? R-21? R-28? etc.
Perhaps it would be more helpful to look at in terms of U-value? I don't know. Either why, I'd like to see the results. I'd be working on the question right now, but it's way past my bedtime. So I'll check back in tomorrow.
And yes, it would also be interesting to simply compare to a baseline such as code minimum. But I'd like to see the entire progression from R-0 on up.
Given that the cost per R is so high with spray foam I would not be surprised if the return on investment did not happen about 4 inches or R28. Given that most people will move before year seven R 4 may not ROI.
I seem to recall that the instructions do not allow much more than 4 inches to be applied per day. Any thicker and the heat generated by curing cannot escape and it may not cure correctly. Doubling the install labor.
Because fluffy insulation is so much less expensive the 20 year ROI comes about R60.
Walta
From what I was told, even after 2" the install needs to be sure their formulation is correct to get to 3 or 4 inches. After that I believe you need to come back an do a second pass.
We need to ditch the idea of ROI in terms of how long you're personally going to live in the house, especially on a green building website. We should all be making decisions like this as if we're going to live there for 50 years, because someone likely will be. If we all did that, then the house you move into would be as good as the house you left. Instead we're trying to saddle the next occupants with our selfish, penny pinching, shortsightedness.
CDN Reno,
Starting with a wall of R-5 and using the rule that doubling the amount of insulation halves the heat loss:
To halve the heat loss you would need to add an additional R-5
To halve it again, you would need to add an additional R-10
To halve it again you would need to add an additional R-20
To halve it again you would need to add an additional R-40
And so on.
At the same time, let's say your heating expense was $1000 a month.
The first additional R-5 saves you $500
The next R-10 saves you $250
The next R-20 saves you $125
The next R-40 saves you $75
An so on.
So yes there is a diminishing return on more insulation of any type, and definitely a sweet spot in terms of ROI.
Yep.
Alternately, for the first R-5 you get $100 per R
For the next R-10 you get $25 per R
For the next R20 you get $6.25 per R
For the next R40 you get $1.75 per R
And so on.
That's what diminishing returns is all about.
Seems like the idea is someone is saying it's exponential, someone is saying it's one-to-one...but in reality it's logarithmic. Growth is super fast at the start, but much slower as it advances logarithmically.
That has to be the correct answer because the final point is set in that at R200 in the real world would change not at all vs R a billion. It seems improbably that someone with R75 is half as great real world use case as the house over with R150. But the person with R10 is significantly better off than the house none.
So we know it can't be one-to-one.
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But log flattens the exponential by removing power.
Seems that "more than 2 is a waste" is claiming exponential growth to RIO.
One-to-one RIO simply can't be the case because it's a real world application where there is a point where more can't equal better at a finite point.
The undefined claim by someone in spray that 2 is it for RIO, it's already a complicated statement. RIO for money? for material? for what.
Most certainly insulation is logrethmic growth. Best at the lowest level, but a natural decrease with added insulation to flattened where it cannot be one-to-one with "more."
Either way, the graph of performance has a definite cut off when the measure is energy loss or human psychical comfort. No one is advocating for R100. So is R49 bad? Heck no. Is R19 at too thick compressed (R18?) vs the right sized R21 truly 17% and cost wise better? Does it really matter much? Probably not right?
Logarithmic returns aside, in case it's not clear, the same issue is true for all types of insulation; spray foam installers are the only ones who routinely try to convince people to use less of it. That's not all bad, as spray foam--even newer formulations--have higher levels of up-front carbon emissions than most of the other options, but it's not a reason to use spray foam instead of another type of insulation.
And the corollary is that the more expensive your insulation, the sooner you meet the point of diminishing returns.
Spray foam salesmen are in the position of saying essentially, since our product is so expensive you should use less of it, and using less of it makes it less expensive.
I don't disagree with the sentiment exactly, but at the same time when you're willing to pay more and they say it's not worth it, it does say something about them as sales people.
If a customer is willing to pay a third more and they counter it's not necessary for 2% more there's a level of honesty there.
You could look at it that way. In my experience, 100% of the time they say it's not worth it because it's spray foam, not because all insulation has diminishing returns.
One of the issues with spray foam is that there is a maximum spray thickness. Beyond that, you have to come back after it hardens and do a second pass. A lot of the cost of foam is the labor, so basically anything thicker than a single pass costs double.
So there is no "a third more." It's X, or twice X. So the sales pitch is that X is good enough, because twice X is too much and too expensive.
I looked at a couple of newer spray foams that have lifts of up to 7” if I’m not mistaken. If that is right it changes cost a bit.
There are major diminishing returns to spray foam, but it’s true for all insulation as well. Insulating is buying future energy today - you’re wagering that energy will get more expensive or at least not decrease in cost much, and that you’ll need the same or more energy in the future. Another way of making the same bet is buying some Exxon stock, which can be resold much easier than insulation can.
Yeah, but Exxon stock doesn't make your home more comfortable and quieter.
Can you tell the difference between R-60 and R-70? R-20 and R-30?
A good article by Allison on the topic: https://www.energyvanguard.com/blog/the-diminishing-returns-of-adding-more-insulation/
I think the problem is that there are too many variables. Since spray foam is not just insulation, it is also air sealing and vapor barrier, some will argue it is better to compare u-values or even k-values of competition. If you consider that the "total" package, then the bar graph from energymodelingagency.com does indeed point at closed cell diminishing returns being at about three inches. However, with modern building products like Zip, tapes, exterior insulations, etc things get muddied. I really think insulation type and thicknesses come down to a case by case basis. I'm currently building a barndominium in which I'm using spray foam on the living section, and blown in for garage attic and I feel comfortable that it is the right choice for my context, since I did not opt to spend the money on the zip system or exterior insulation. It is also 1.5 story so space is limited in the house part of the building. If I was building a traditional house I would do 1.5in rockwool exterior insulation, and either of 2x6 or even a 2x8 wall filled with rockwool which I think would be around R40 and airtight with Zip, which would probably be better.
Everything in construction is subject to diminishing returns.
Including happiness.
A more absolute perspective can help here. Depending on temperature extremes, the "super-insulated" threshold is crossed at a composite R-value of between 40 and 50 (YMMV). At that point and beyond, heat flow becomes insignificant.
So a good approach would be to compare performance/cost against that target, or perhaps a lesser one with higher annual energy costs, Ex. spend $50/yr more ongoing to save $500 on the project now.