Insulation Upgrade on Cape House
I’ve been haunted by Martin’s cape roof advice for some time now.
When dealing with old, poorly insulated capes (1.5 story structure with kneewalls and tiny attic) Martin has suggested the following:
“Exterior rigid foam is by far the best solution to the problem [of a poorly insulated cape].”
“Is there any good solution to a poorly performing Cape? There is. The necessary roof insulation has to be installed above the roof sheathing. To learn about this type of fix, see How to Install Rigid Foam On Top of Roof Sheathing.”
Ok. It’s the best. But what does it mean to be ‘the best’ solution? Highest performing? Sure. But is it sensible from a resource allocation standpoint? Martin does admit there are lower cost alternatives. But then which approach– wholistically– is actually ‘the best’?
I ask as someone tasked with making this decision (it’s reroof time!) NOT on my own house and NOT with my money, but on behalf of a non-profit organization. I have to show the organization that does own this structure (their office) that it is actually ‘the best’ solution–if it is. ‘The best’ doesn’t need to be a pure monetary ROI– it can include things like environmental concerns (its an environmental organization), comfort (the upstairs does get very hot in summer), resilience, etc.– but they do need to be tangible things that a board of directors would understand and appreciate and see as being a wise (not emotional) investment. AND they need to be things that cannot be otherwise achieved for cheaper!!
Part of the big picture goal does include improving the shell so heat pumps can be used as a primary heat source. Basement has already been well insulated. But in line with the point above: could a cheaper set of work be done to accomplish this goal (even if end performance is not quite ‘the best’)?
What say you, would you ‘sell’ this fix or would you just crawl into the attics and do what you could with sealing/insulating the existing planes?
Happy to provide more info as needed.
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Replies
Tyler,
There's really only tradeoffs to be made for different situations. The cold vented roof accomplishes many things outlined in the article. It has a lot going on for it:
In order of what I would consider the benefits -
1. You're no longer limited (dimensionally) in the R value that can be added.
2. You often don't need to modify the interior attic space if it's being used.
3. You increase the dew point of the original sheathing, extending its life.
4. You add a primary, secondary, (and tertiary with 2x4's on the flat) drainage plane
5. You allow subsequent roof replacements with relative ease, without running the risk of intermittent leaks.
It has inherent drawbacks
1. Cost - rigid insulation is the most expensive available, compared to loose fill fiberglass.
2. Trim modifications
3. Long screws - adds up quicker than you'd expect
4. Long screw misses - Practice here takes a while too
5. Attic needs to be sealed - something that may be difficult to do well as a retrofit.
There really is no sell on whether it's the best. If it's for a non-profit without a lot of money, cheap labor goes far with inexpensive materials. If time and continuity of operations is a concern, exterior insulation may be ideal.
I've built one roof like this, and it wasn't difficult per se, just different and a little more time consuming. I could probably build it again with only a 50-60% increase in time compared to probably 200% that it took me on the first one.
Thanks for your thoughts Kyle.
Its true that there is not a 'right' answer (like with most anything) but, in a subjective sense, there is such a thing as senseless work and such a thing as sensible work. I would want to ensure that this work doesn't fall under the category of senseless. Its difficult to quantify the variables here and make even a subjective determination.
To some degree I am becoming more and more perplexed by what criteria is being used for some of the statements made by GBA authors over the years. It seems like many statements are based on performance as the sole metric, but frankly that's a bit useless. And where there is true wisdom (and I do believe that does exist here) it can be hard to know that you are on the receiving end of wisdom since it's all written word and very impersonal.
I do see a fair few voices offering qualifications to the performance metrics, but GBA (an amorphous entity I realize) sometimes feels like one giant contradiction. For the way my brain works, it leads to some serious pretzel brain and cognitive dissonance.
My local energy auditor seemed to balk at the idea of the project. Their job is trimming low hanging fruit of course.
"To some degree I am becoming more and more perplexed by what criteria is being used for some of the statements made by GBA authors over the years. It seems like many statements are based on performance as the sole metric, but frankly that's a bit useless. And where there is true wisdom (and I do believe that does exist here) it can be hard to know that you are on the receiving end of wisdom since it's all written word and very impersonal."
Often times performance *is* the sole metric, when discussing a new method or new product, as it is useful to know if it performs well or not regardless of the cost. It's certainly only one piece of the puzzle.
Otherwise, and I mean this in the most sincere way possible, I think you need to step back a bit and take it a little less seriously. Most of us are only giving what experience we have, and some combination of the research we've done, from authors that are reputable. There's countless studies available, dating back to the 1900's on building science as we know it. It's impossible for any of us to be an expert by experimentation, there's simply too many fields and not enough time or willing clients. You'll never really know if we're blowing smoke or giving good advice until you ponder on it for a while, see if it meshes well with other research or evidence, and decide that it's good or not good.
There's a lot of hype and marketing that exists everywhere. Products or methodologies get hyped for even long periods of time before it's discovered that it's no good. Take the Masonite, early LP siding, cardboard sheathing, EIFS, cinderblock (not cmu), and a longer list of products. People were told they were great. Some listened, some didn't, and there really wasn't any way to tell in the early phases.
FWIW, double stud walls, closed cell spray foam, strict adherence to "advanced framing", perforated house wrap, thick Zip R, and many other hot products are probably going to end up there as well one day. Physics is physics, and the rest is cost.
I'll admit that I've had the wool pulled over my eyes too - some products seem great, until you inspect their properties, and they're just OK except for one metric or another, at 2-5X the cost. It takes some time to be able to see through the fluff.
>"5. Attic needs to be sealed - something that may be difficult to do well as a retrofit."
Can you expand on what you mean by this? Like an access hatch you mean? How does the rigid foam over the roof change this situation?
If you choose to insulate the exterior of a structure, or part of a structure, you don't want the outdoor atmosphere to enter behind it. Meaning, that you could insulate the roof deck until the cows come home, but if you had any soffit vents in place, it wouldn't do a single thing. The roof needs to be 'encapsulated' so that air leakage is minimal, so that the insulation can do what it was designed to do, resist the flow of energy. A stream of air behind the insulation effectively shorts it to ground. In the roof deck scenario, you ideally wouldn't even want insulation on the attic floor any longer, and thus wouldn't need to worry about sealing any attic hatches, with a lot of caveats to that last statement.
thanks, I see what you mean now.
Perhaps another way to phrase this entire question is:
Should everyone with a leaky, poorly insulated cape in a cold climate seriously consider this work? Given access to the needed capital.
Or is it just for people who want to hit some benchmark for emotional reasons? (Which if you can't tell, I can be that latter person too easily, so I am trying to check myself as needed).
"Should everyone with a leaky, poorly insulated cape in a cold climate seriously consider this work? Given access to the needed capital."
I'll go off script here and try to address the two parts of this question as I see it. One is about the fundamental features/failures of capitalism, and the other is about improving existing structures. Given that it's time, money, and resource ahead to retrofit a structure where it can be done, of course we should fix up all those cape houses that are structurally fine, but energy nightmares. They're bad. Maybe charming, maybe cozy, but atrocious when we're talking about efficiency. That's something of the role of the government, to try and incentivize taking action where it can, for those who are near the edge on affording it. Efficiency directly translates into financial expenditures, and more often effects those who can't afford to do anything about it. (I'm talking middle class families here, with two working adults, not people living paycheck to paycheck. It's even worse for them).
The reduction inflation act went a long way in this - if you read what's available now, there's a 30% rebate on a *lot* of improvements that I think make it possible to retrofit where as before it would have been uneconomical. Insulation qualifies, doors, windows, tape, caulking, heat pumps, you name it. You could probably even fib a little, there's a lot of room for interpretation.
Obviously, if everyone had infinite cash, we'd fix them up, tear them down, and do it all over again. But if someone chooses to go above whats minimally required, I don't think it should be seen as being gluttonous. We're allowed to allocate our resources as we wish, and everyone has different priorities.
If someone chooses to insulate their rafters vs using blown in insulation, just for the sake of never having to walk through blown in fiberglass again, so be it. If someone wants to insulate their house with 6" of mineral wool, that's ok too. Both can be seen as excessive from a outsiders perspective, but such is life.
maine_tyler,
"Should everyone with a leaky, poorly insulated cape in a cold climate seriously consider this work? Given access to the needed capital."
No. They have to weigh the four factors and see if it makes sense in their particular situation. I think you outlined them in your first post, and I'm not sure it's any more complicated than that.
- Is there a realistic ROI?
- Does the work need to be done to preserve the structure, or prevent it from deteriorating?
- Do they feel the reduction in energy used vs the materials necessary are useful or meaningful from an environmental standpoint.
- Is there a significant increase in comfort?
Malcolm and Kyle,
I do really appreciate these thoughts and it has helped me. If I seem frustrated, its really only at myself, or perhaps the internet in general :). At the end of the day, I shouldn't ask too much of an online forum.
Malcolm, I like the 4 factors you mention. I suppose I would like to see studies / breakdowns of when an over-roof style retrofit is needed to hit those factors (to some quantified benchmark) vs lower cost alternatives. That's a big ask, but it's the kind of info I think we should generally seek to gather in terms of big picture green building questions.
I know a lot has been said about the low returns on deep energy retrofits, and this sort of falls into that category I suppose, but addressing all 4 (or so) factors would be interesting.
As much as part of me hates the way computer tech has entered our lives, I still dream of an algorithm that can make 'perfect' decisions using huge numbers of variables-- more than our brains are equipped to do most of the time. Could lead to utopia, or just as easily perhaps dystopia.