Second Guessing an Insulation Upgrade
A homeowner has added a layer of rigid insulation to some interior walls, and now wonders if he’s made a big mistake
Is there anything worse than getting midway through a renovation and then suddenly wondering whether you've got some important detail all wrong?
That seems to be the predicament of William Lucrisia, who's in the midst of an insulation upgrade at his house north of Seattle.
"The house was heated by propane," he explains in a Q&A post at Green Building Advisor. It was a cost that was hard to get hold of, especially with some of the design [features] of the house (high ceiling)."
So Lucrisia set about making improvements, and his plan involved gutting interior walls and adding mineral wool insulation and then a layer of foil-faced polyisocyanurate insulation before applying new gypsum drywall.
"I am a bit 'OCD' now that the living room is for the most part done... I wonder if I am trapping moisture inside my walls, having used the foil-faced polyiso just behind the Sheetrock... Was it okay to do what I have done?"
That's the question for this Q&A Spotlight.
The walls are OK, but what about the ceiling?
The foil face of the polyiso insulation won't allow the passage of moisture, but Lucrisia should have no problems as long as the walls can dry to the exterior, says GBA senior editor Martin Holladay. And that, Lucrisia says, appears to be the case.
"I presume things will dry from the exterior," he writes. "It's typical sheathingMaterial, usually plywood or oriented strand board (OSB), but sometimes wooden boards, installed on the exterior of wall studs, rafters, or roof trusses; siding or roofing installed on the sheathing—sometimes over strapping to create a rainscreen. and siding on the exterior. It's just that my wooded area with the rain and cool air air scares me with some of the stuff I have been reading lately."
But a related issue concerns the ceiling. A second photo that Lucrisia posts with his question shows a ceiling finished with slats of wood, and Holladay wants to know whether there's a good air barrier behind the boards.
Lucrisia explains the wood ceiling consist of slats secured to 24-inch o.c. nailers. They are essentially a decorative detail, applied over an existing ceiling. "There is about one inch between the slat assemblies and the Sheetrock on the ceiling," he says. "I never disturbed the makeup of the ceiling. Drywall-[vapor barrier]-insulation."
Adding more insulation to the attic
In Lucrisia's staged approach to an energy retrofit, increasing attic insulation is still on the to-do list. When the time comes, he plans to blow in cellulose over the insulation that's already there.
Dana Dorsett suggests additional air sealing first. "You can leave the existing attic-floor insulation in place," Dorsett writes, "but air-seal all penetrations before adding more. Wrap R-15 rock wool around any flues or chimneys (tied in place with steel wire, or wire fencing) to keep cellulose from contacting them."
Will mold be an issue?
Richard Beyer believes Lucrisia will be fine with the polyiso he's installed, but he raises questions about another potential problem with the assembly.
"This installation is fine as long as you tape the seams and maintain the indoor RH (humidity)," Beyer writes. "If not, mold is inevitable in time. I visited two homes where this was the installation system. One with fiberglass and one with open cell foam. Both homes did not have controlled humidity and ventilation systems. Both ended with sickness and asthma-related issues.
"Fortunately for both homeowners the problem associated with their health was located inside their walls," Beyer adds. "Not everyone living with mold is as fortunate."
Writing from upstate New York, AJ Builder finds Beyer's suggestion of a potential mold hazard amounts to scare-mongering. "Millions of homes have no problems," AJ Builder says. "But what, no diabetes, no big blood pressure from worrying about the mold? Your posts are out of line with mainstream home ownership. The sky is not falling. Yours is. Most are not. Mine is not."
"I'm sorry you are offended by factual posts," Beyer replies. "Maybe you can explain why both of these homeowners became so sick? Maybe black mold is good? This is as real as it gets!
"It certainly blew my mind when we opened the wall and saw black mold. I'm pretty certain many homes with tight wall assemblies have some form of mold problems when moisture is not controlled. If it was not a problem, explain why there's so much focus on air exchange and dehumidification today, AJ. Are you one of those guys installing humidifiers on HVAC(Heating, ventilation, and air conditioning). Collectively, the mechanical systems that heat, ventilate, and cool a building. systems?"
Mold threat is overstated
Indoor relative humidity can get so high that mold growth results, Holladay says, but this is relatively rare. Most homeowners run their bathroom exhaust fans enough to prevent mold growth. "There is no reason to believe that an interior layer of polyisocyanurate on exterior walls will cause health problems for homeowners," Holladay writes.
Mold points to elevated moisture levels, he says, so if you see mold, try to determine why it's there, and then find a way to reduce moisture.
Holladay adds a quote from the Centers for Disease Control and Prevention web site: "There is always a little mold everywhere — in the air and on many surfaces. There are very few reports that toxigenic molds found inside homes can cause unique or rare health conditions such as pulmonary hemorrhage or memory loss. These case reports are rare, and a causal link between the presence of the toxigenic mold and these conditions has not been proven."
But Beyer is adamant. "I'm just the messenger and reporting what I witnessed," he says.
"Maybe mold is a hoax to rob people of their money?" he continues. "Maybe you have an answer as to why there's a mold exclusion in all of our insurance policies? I now wonder what all of those mold remediation companies do in their down time since mold is such a rare occurrence in homes?"
He also points to a statement from the American Lung Association, which suggests mold can trigger allergic reactions and asthma symptoms in some people.
And then there's the Corvette connection
As much as Lucrisia has profited from the discussion, he calls for a truce and points to his association with a forum for Corvette aficionados as a model. "We cautiously give advice to 'younger' members: the power of a Corvette can kill you as it is," he says. "But us old timers typically want to provide answers to questions (usually posed by newbies) to help them with their mechanical issues — and typically close with, 'Be careful.'"
And so it is with his post to GBA, only in this case it's Lucrisia who's the newbie. "To all of this," Lucrisia writes, "I saw no mold in my walls before my demo — I did what I did — I have elevated [humidity] levels in my living space and I am trying to rectify this condition through crawl space encapsulation.
"To all the other DIYers with thoughts of doing what I did? Well, if you own a Corvette and have issues send me a note. I will do the best to help you and tell ya to be careful."
Our expert weighs in
GBA technical director Peter Yost added these comments:
After a bit of additional information directly from William Lucrisia, here is how I would sum up this discussion:
Measuring relative humidity: William has assessed interior moisture using Acurite humidistats (such as the ones you can get from The Home Depot). I can’t find any specs on the accuracy of these humidistats, or compliance to any standard of +/- accuracy, but I have found inexpensive hygrometers of this sort to be of very questionable accuracy, and not in any linear way (that is, that they don’t tend to always read high, or low, or that they are off by the same amount over their measurement range. They tend to get the air temperature pretty well, but not the relative humidity.
Even “good” hygrometers, such as those in Onset HOBOs or in a tool like the Omega 4-in-1 meter, the stated accuracy is around +/- 3% on RH, and $10 or so hygrometers like the Acurite are far less accurate. So, even though I am unaware of any ASTMAmerican Society for Testing and Materials. Not-for-profit international standards organization that provides a forum for the development and publication of voluntary technical standards for materials, products, systems, and services. Originally the American Society for Testing and Materials. standard for assessing/reporting hygrometer accuracy, look for ones that at least publish their error bands (but click here for an interesting assessment of electronic hygrometer accuracy).
Interior RH of 68-70%. Having said the above, William is reporting mighty high interior wintertime RH, even for his climate. If you manage energy better, you have to manage moisture better. Part of managing moisture better is to identify interior sources (like the damp clay soil in William's crawl space). It’s pretty clear the exposed soil in the crawl space section of his home is one, or even the, likely problem, and William is right on that.
Assessing airtightness. On any energy retrofit, and particularly one like William’s that is fairly intensive and extensive, identifying and managing air leakage is critical. I strongly recommend that William’s work and other projects like it be guided by a complete building performance audit. To manage energy and moisture with equal intensity means going after air leakage first (because air leakage carries so much wetting potential with it). And if you can’t or won’t spring for a whole house performance audit to identify your specific air leakage, at least use the EPA Energy StarLabeling system sponsored by the Environmental Protection Agency and the US Department of Energy for labeling the most energy-efficient products on the market; applies to a wide range of products, from computers and office equipment to refrigerators and air conditioners. Thermal Bypass checklist as your guide.
- William Lucrisia
Dec 9, 2014 6:42 PM ET
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