How much rigid foam insulation (polyiso) can be installed on the exterior of a building and still be able to install siding such as Hardiplank?
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I am doing a whole house remodel/addition and am looking to maximize insulation without decreasing interior space, so would like to install as much as possible on the exterior and use spray foam in the 2×4 wall cavity.
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This may help. The REMOTE wall they use has 6" of XPS in it. http://www.cchrc.org/walls I think there is another question about this here, too. I've read so much lately I don't recall if it was here, on healthyheating, or where. 2" of XPS on the outside is pretty common here, and a friend installed wood siding over that 30 yrs ago; I'm sure he is not the only one.
I think you could go to 1 1/2" and still nail with 16d splitless nails. Hardie is usually blind nailed at the top of the panel, the nails being hidden by the next lap. I would consider blown insulation in the wall cavity.
However much you decide to install, I would advise against foil-faced polyisocyanurate. It will eliminate any potential for drying to the exterior. XPS has some minimal vapor permeability. Foil is the perfect vapor barrier, and can create as many problems as it's intended to prevent.
Joshua,
A lot of builders are using two layers of 2-in. polyiso (for a total of 4 inches of foam). See this video:
https://www.greenbuildingadvisor.com/video-leed-platinum-habitat-humanity-house-westford-mass
Here's a retrofit job with 4 inches of polyiso:
https://www.greenbuildingadvisor.com/homes/old-house-gets-superinsulation-retrofit
Martin,
I can almost understand how the new construction project that you referenced is a reasonable "managed risk".
The new projects seem to be airtight....As they should be... just look at the coaching and how much "gooey stuff" they use ;-)
I continue to be squeemish about the retrofit.
My understand is that even with the "A team" contractors and with "A team" coaching.... the retrofit is still not exactly airtight.
Warm and moist air is still passing thru the enclosure.
Just think what would happen if the "A team" was not involved!
Should kids be allowed to try this at home?
Is not the real reason behind the aggressive Passivhaus airtightness standard (0.6 ach50) because of durability concerns with high levels of insulation?
I still do not understand Robert Riversong's concerns about Negative Ion counts. :--)
But his concerns about less than perfect air barriers combined with high levels of insulation and a vapor barrier does make sense to me.
I realize that I tend to be an alarmist and a chicken little.
John,
I recently heard Paul Endrenkamp give a presentation about the riskiness of superinsulated assemblies. Paul points out the riskiness of doing nothing -- that is, allowing the global climate change phenomenon to roll over us as we boil like frogs in a warming pot.
Builders need to show leadership. In some cases that may mean making decisions on building assemblies using a calculated assessment of risk. Paul acknowledges that some questions remain unanswered; that doesn't mean we shouldn't act.
Personally, I would be willing to take the risk of installing 4 inches of exterior polyiso in New England. Here's my own challenge: let's point to the failures. I love failure stories. Anyone got a good thick-exterior-foam failure story? If not, let's all keep working together to come up with good retrofit solutions.
Martin,
Does this example in Lexington KY count?
How about Joe's Barn?
Stuff happens
http://www.buildingscience.com/documents/insights/bsi-036-complex-three-dimensional-air-flow-networks/?topic=/new-documents
John,
It's great to study examples like the two you provided. The take-away lessons:
1. Don't forget that every building needs an air barrier.
2. With exterior insulation, it's best to have at least two layers with staggered joints.
Good lessons. We're all learning. But I think that most of us know those lessons by now. By the way, Joe's barn is doing fine.
Martin,
Did you notice that all of the "failures" /embarrassments were compact VAULTED roof assemblies?
John,
Like you, I'm a fan of unconditioned attics. But it is possible to build an insulated sloped roof that performs well.
What is it that you don't understand? The myriad, scientifically and empirically proven physical, mental and emotional benefits of negative ions or the fact that plastics remove them from the interior environment and falling water and earth materials increase them?
Negative ions are odorless tasteless molecules that are breathed into our respiratory system. High concentrations of negative ions can be found in nature in mountain forests, waterfalls, and beaches where people feel energized and invigorated, which helps relieve stress, alleviate depression, boost energy.
Scientific studies have shown that atmospheres charged with negative ions relieve hay-fever and asthma symptoms, seasonal depression, fatigue and headaches. It's also been shown that negatively ionized atmospheres improve performance of voluntary movement, increase work capacity, sharpen mental functioning, and reduce error rates.
Studies at Columbia University and the New York State Psychiatric Institute have demonstrated that High Density Negative Ionizers appear to act as a specific antidepressant for patients with seasonal affective disorder (SAD).
Remarkable as it may seem, a room charged with negative ions was shown to stem bacteria growth and precipitate many airborne contaminants including pollen, dust and dust mites, viruses, second-hand cigarette smoke, animal dander, odors and toxic chemical fumes.