Gregg Zuman’s house in Beacon, New York, was built near the start of the Civil War, and like most any building of that era it’s in need of a few repairs. At the moment, Zuman is stuck on what to do about the clapboard siding.
“It’s slathered with lead paint, of course,” Zuman writes in a Q&A post. “The issue is how to move ahead: figure out a way to remove the lead paint and apply a coat of 50-50 pine tar-raw linseed or cut losses, remove the old clapboard, replace with cedar clapboard, and apply 50-50 pine tar-raw linseed or suck it up, paint over the lead paint with decent lead-free paint, and embrace compromise.”
The cheapest option probably will be painting over the lead paint, but Zuman worries that would make the wall a vapor impermeable barrier — something he wants to avoid at all costs.
The house is balloon framed, with no space between the framing and the siding — meaning no sheathing. Zuman plans on using Airkrete insulation, and his overall objective is to “honor the history of the structure while updating the materials were needed with products free of fossil fuels.”
How does he proceed? That’s the issue for this Q&A Spotlight.
This wall needs a rainscreen
Lead is an obvious concern, says GBA senior editor Martin Holladay, and any prep work on the clapboards will need the help of a contractor who understands and follows lead-safe procedures. Even if the lead problem can be solved, however, Zuman will have a wall without an effective air barrier.
“If you leave the existing clapboard in place, you’ll have a wall without a rainscreen and without a decent exterior air barrier,” he says. “(Airkrete has a tendency to shrink away from the framing, so the Airkrete won’t be airtight).
“I advise you to install new sheathing (installed in an airtight manner), new furring strips to create a rainscreen gap, and the siding of your choice. You’ll have a much better wall if you follow this advice.”
Dana Dorsett also would like to see Zuman introduce a gap behind the siding.
“Leaded paint is a true vapor barrier,” Dorsett says. “If it’s clapboards nailed directly onto the balloon framing (no plank sheathing) insulating the cavities will almost certainly cause the paint to fail in short years due to the high moisture content of the clapboards, followed by the nails &/or the clapboard itself.
“It has survived until now due to the clapboards’ ability to dry quickly into the empty framing cavities,” Dorsett continues. “That rapid drying will no longer happen if the insulation is allowed in contact with the clapboards. Whether keeping the original clapboard or installing new ones, providing at least a 1/4-inch deep (1/2 inch would probably be easier and better) vent cavity between the clapboards and the insulation would provide significant mitigation against those issues.”
The paint will not be a vapor barrier
Zuman wants a vapor-permeable wall system, and one of his concerns is that the lead paint on the clapboards creates a vapor barrier. Should be be concerned?
Not really. Although, as Dorsett points out, lead paint is a true vapor barrier, as a practical matter that won’t be a concern here.
“While Dana is correct that a perfect coat of lead-based paint, adequately thick, is a vapor barrier, you aren’t legally allowed to have that,” Holladay says. “You’ll end up with old clapboards that have been scraped and prepped (using lead-safe practices) and coated with a modern lead-free paint.
“So if you keep the old clapboard and repaint it, you won’t have an exterior vapor barrier. You’ll have old clapboard with some flecks of older paint still clinging to it, but you won’t have 100% coverage of lead-based paint.”
The only real concern with lead paint is the toxicity of the lead, a particular risk for any children or pregnant women who may be living in the house.
Keeping the house fossil-fuel free
Zuman doesn’t want materials in the house that are made with fossil fuels, so he’s turning to alternatives such as Airkrete (an insulation whose principal ingredient is magnesium oxide), magnesium oxide board sheathing (MgO board), and (for the roof) Pavatex, a European wood fiber insulation.
“Basically all house builders until the end of WWI crafted homes using nontoxic materials,” Zuman writes. “Since my house is in New York, I’ve chosen to insulate the roof with a material that’s non-toxic and produced from a regenerative resource (cellulose has its own issues, though it was my first choice until I executed additional research). Sadly, the house building industry in the States, in my humble opinion, is stuck with sub-par options on so many levels.”
Holladay notes that because Pavatex must be shipped from Europe to the U.S., there’s a fair amount of fossil fuel consumption involved in transportation, even if the product itself isn’t made with a petroleum-based foam.
But Zuman argued the fuels used in the final delivery of a product aren’t significant in relation to the energy that went into developing and manufacturing.
“The embodied energy involved in producing the inputs and in producing the logistics related to production of the inputs of a final product typically so far outweighs final delivery mileage that I don’t even consider such miles as relevant,” he says. “That noted, shipping items between places is about 10 times more efficient on a fossil fuel basis than motor trucking items.”
Further, Zuman’s assertion that houses built before World War I are made with less toxic materials than houses today is just plain wrong, Holladay and others say.
Lead-based paint dates to colonial times, and asbestos was first mined for use in insulation in 1858, he says. Steve Knapp adds that asbestos shingles and siding were introduced to the U.S. in 1907, while lead solder, coal and wood fires, and open-flame lighting all were environmental and health hazards that were common before World War I.
Old houses have their challenges
As Zuman, a first-time homeowner, ponders the complexities of saving an old house, he wonders just what he’s got himself into.
“Tough choice here,” he writes, “as the more I remove from the structure, the more of a fool I feel —
what did I purchase again? I’ll be left with the balloon frame, the masonry, and the stone foundation including a stone lower floor wall that’s an insulation challenge all in itself.”
Installing new cedar siding would strip the house of some of its character and history, but whatever he does will not be cheap. His plan is now to work with a local contractor who will “scrub the siding and see how it goes.” The idea is to clean up the existing siding as well as possible before coating it with a mix of pine tar and raw linseed oil, or another vapor-permeable finish.
John Clark admits he’s not a huge fan of old wood houses, and says the real answer to Zuman’s problems may be a bolt of lightning.
“Yes, as in ‘burn it down’ (I’m joking, kind of),” Clark says. “I don’t put much weight in the historical value of old wooden homes. They’re usually drafty, have odd dimensions, short ceilings, have structural issues, and much of their ‘value’ is locked up on the lot itself.
“Conversely, you could always do a gut rehab and just get it fixed,” Clark continues. “Maybe look into a HomeStyle Renovation Mortgage where the cost to renovate is no more than 50% of the ‘as completed’ value of the home.”
Our expert’s opinion
Here’s what GBA technical director Peter Yost has to say:
One option may be to encapsulate the lead paint on your siding. And I say this because you may have to limit the investment in your exterior wall cladding since you have so many other bigger fish to fry. Many years ago here at the BuildingGreen offices in Brattleboro, Vermont, we used LeadLock. (Our offices are located in the former Estey Organ Factory, once the world’s largest manufacturer of parlor organs).
I agree that some sort of back-venting of your cladding is a good idea to maintain drying potential as you fill framing wall cavities with insulation. You should take a look at this GBA case study, where Jeff Medanich tried several different approaches to keeping existing siding in historic, originally unconditioned wood-framed cottages in Boulder, Colorado (admittedly, a drier climate than what you’re dealing with).
I have always had reservations about AirKrete Insulation. Whenever I have asked the company about how well AirKrete stays bonded to surfaces like wood framing and sheathing — which tend to move quite a bit over time — they have stated they can add a proprietary agent to increase the material’s flexibility and bonding capabilities. Add? Why not require it or include this material automatically? A check of the AirKrete website reveals nothing about the airtightness characteristics of the material or any installations. I reviewed the sample specification offered on the AirKrete website and it includes nothing on airtightness. It does contain some woefully outdated text on “Vapor/Weather Barriers.”
Then there is a photo in the AirKrete photo gallery. It shows AirKrete being injected into an existing brick wall assembly — presumably brick veneer — filling the dedicated free-drainage and capillary space between the veneer and the rest of the wall assembly! Not every space should be filled with insulation! Sometimes spaces have a reason for being.
And as luck would have it, there is a new retrofit installation of AirKrete just accomplished in the last several weeks in my neck of the woods. It’s an historic wood-framed meeting house in northeastern coastal Massachusetts, with AirKrete used as cavity insulation. The retrofit project has been set up with a series of HOBO data loggers to measure conditions in the building space as well as sensors in walls. I will be working with the consultants on this project to see how the walls perform over time, including infrared imaging when depressurized to assess airtightness — stay tuned!