Image Credit: Justin Brown The foundation is a mix of poured concrete and fieldstone, each with its own insulation challenges. Brown has covered the crawl space floor with a 6-mil plastic vapor barrier. Part of the foundation is made from fieldstone. Brown has insulated the poured concrete foundation walls with 3 inches of Dow Thermax insulation. The rim joist has been insulated with 2 inches of extruded polystyrene and spray foam. Kick-out flashing where the roof meets a sidewall would divert runoff away from the building.
In coastal Massachusetts, Justin Brown is looking for ways to upgrade the energy performance of his very old house. It sounds as if previous owners had taken some steps to tighten up the building envelope, but they didn’t go far enough with either air sealing or insulation. Now, Brown wants to complete the job.
One area of particular concern is the attic. It’s insulated with a mix of fiberglass and cellulose, he writes in a Q&A post, but a cold snap this winter produced some frost on the underside of the roof sheathing.
Completing the insulation of the foundation walls also is on Brown’s to-do list (see the floor plan and images below). The foundation is a mix of poured concrete and fieldstone, and while Brown has added 3 inches of rigid insulation to the concrete foundation walls, the fieldstone walls remain to be done.
“I spent hours digging through cellulose and air sealed some wall plates and open wall cavities that the previous homeowner’s air-sealing and insulation contractors clearly missed,” Brown writes. “There is one 30-foot exterior wall plate in the eaves I cannot reach to air seal from inside the attic.”
The 10 recessed lights in the attic floor have been upgraded with LED airtight retrofits, but are not covered with any insulation. In the basement, the rim joists have been insulated with 2-inch extruded polystyrene and spray foam. But the inside of the foundation walls, a mix of poured concrete and fieldstone, have not been insulated.
Brown has found an ally in his efforts to upgrade. Technicians from Mass Save, a utility energy efficiency program, have visited the house and are offering to remove the existing attic insulation, seal any air leaks that have been overlooked, and add insulation to bring the entire attic up to R-49. After a 75% rebate, Brown would pay $500.
“Is it worth pulling the exterior soffit/fascia board to seal that 30-foot exterior wall plate?” Brown asks. “I have a hard time quantifying how much air loss that will stop. Mass Save says they won’t do that; it would be up to me.
“I know quantifying [return on investment] is tough, but will I see substantial benefits going from R-30 to R-49 and really burying the recessed lights in cellulose?” he continues. “I was estimating about a 5-year payback.”
That’s the topic for this Q&A Spotlight.
Mass Save’s offer is a “bargain”
GBA editor Martin Holladay urges Brown to jump on the Mass Save offer for attic improvements.
“The air-sealing work being offered by Mass Save (for just $500) is absolutely worth the money,” he says, “and the upgrade from R-30 to R-49 is being thrown in for the same price. So do it! It’s a bargain.”
The case for pulling the soffit and fascia to allow access for more air-sealing work is less compelling. “There is no easy way to estimate the value of pulling the soffit and fascia to gain access to the area for air sealing,” Holladay writes. “Do it if you can afford the cost — skip it if you can’t.”
David Baerg suggests that sealing air leaks in the attic is crucial if Brown wants to avoid moisture problems in the future. “If you have enough air leakage to cause moisture problems in cold weather, insulating without air sealing will make the problem worse,” he says. “The attic will be colder and, therefore more condensation will occur.”
Brown now uses about 450 gallons of fuel oil a year for heat and hot water. Baerg doubts that Brown will see a five-year payback by increasing attic insulation from R-30 to R-49.
“That upgrade is marginally worth it where I work (northern Ontario — much colder with higher fuel prices),” he says. “Do it to make your house more comfortable and reduce ice dams, and expect a 3%-5% reduction in your oil bills.”
Are the can lights a problem?
Recessed lights are a well-known source of air leaks, Baerg adds, and even the sealed LED fixtures Brown mentions may not be as tight as they seem.
“Did you have a blower door test done?” he asks. “Did your advisor find significant leakage at the recessed fixtures? Even if they are ‘airtight’ they can still be improved. There is likely leakage through the wire channel — caulk this from the attic. And the seams in the can likely leak a bit — seal them with aluminum foil duct tape. And, of course, put a bead of caulking between the can and the ceiling from below.”
The recessed light retrofits are gasketed, Brown replies, and seem tight to the ceiling. But he wonders whether it would be a good idea to build airtight boxes out of 1-inch rigid insulation and cap the fixtures in the attic before any additional cellulose is blown in.
“Installing LED retrofit kits with gaskets cuts down on air flow through a recessed can, but doesn’t stop the air flow completely,” Holladay says. “If I were making the decision, I would retrofit some type of airtight cap over each recessed can.
“But it’s fussy work,” he continues, “and the decision depends in part on how many recessed cans you have to address, how easy or difficult the access is, and who’s doing the work (and at what cost).”
Holladay suggests using foil-faced polyisocyanurate because it’s easy to tape.
Work in the basement
The basement insulation question boils down to this: Will Brown be wasting his money if he adds rigid insulation to 70% of the walls while leaving the remaining 30% uninsulated? That’s what the technicians from Mass Save tell him, but Baerg is among those who disagree.
Go ahead and insulate the poured concrete foundation walls, he advises, and Dana Dorsett is quick to agree.
“Heat loss is a U-factor times area type of thing,” he says. “It’s definitely not a waste of time to fix 70% of the total area.
“Only 2 inches of polyiso won’t get you to Massachusetts code minimum (= R-15 continuous insulation),” Dorsett adds, “but it’s still way better than nothing. Depending on how much above-grade exposure you have on the foundation, the basement losses (even at cooler basement temperatures) can be 20% or more of the heat loss. Fixing 70% of that with even R-12 (2 inches of polyiso) would result in more than a 10% reduction in overall fuel use, even if the 30% of the basement that’s fieldstone is left uninsulated.”
And if he does go ahead with insulating the fieldstone foundation walls, Holladay adds, closed-cell spray polyurethane foam would be the best route. “Not cheap,” he says, “but effective.”
For the fieldstone portion of the foundation, Dorsett suggests 1 inch of closed-cell foam followed by blown insulation in a 2×3 stud wall. That, he says, would get Brown to the code-minimum requirement for basement insulation in a Climate Zone 5A location. But using cellulose in that application could be risky, he says, because in the event of even a minor flood the cellulose would draw up any bulk water “like a sponge and take forever to dry.” Blown-in fiberglass wouldn’t have that problem.
One last note, Dorsett says: Adding between 2 1/2 inches and 3 inches of polyiso on the concrete portion of the foundation rather than the 2 inches Brown has in mind would help him meet code code requirements. Green Insulation Group might be a good source of reclaimed insulation, Dorsett says.
Insulation and moisture control
There is one wrinkle in the insulation picture in Brown’s basement. He writes that the outside of the basement walls are insulated with what appears to be 2 inches of polystyrene (either extruded or expanded), leaving 2 or 3 feet of foundation above grade.
How does this affect the ability of the concrete to shed moisture, especially in light of his plans to add additional insulation on the interior?
Dorsett offers this assessment: “If the exterior polystyrene insulation is only below grade, it has only minimal affect on the drying capacity of the foundation, but it does limit the rate that ground moisture can reach the walls, and raises the temperature of the concrete, helping it dry toward the interior.”
Brown plans to end the interior insulation 1 foot above the basement floor to make absolutely sure that it doesn’t wick up any moisture. If he does that, Dorsett says, moisture wicking up from the footing will be able to dry reasonably well to the interior.
But a 1-foot gap is too much, Holladay tells him. “If you are worried that moisture might wick up the polyiso, you can stop the polyiso 1 inch off the floor,” he says. “But 1 foot is too much -— it just means that your wall isn’t fully insulated.”
Our expert’s opinion
Peter Yost, GBA’s technical director, added these thoughts:
We often follow up with folks whose posts lead to these Q&A Spotlights. We’re looking for additional information about their projects so we can make the response at the end of the blog as helpful as possible. But boy, did we hit gold with Justin Brown!
Justin not only provided a ton of useful photos (see photo gallery), but he also drew up a foundation plan to orient us and has responded in detail to a host of follow-up questions that I posed.
Here is what we have learned, and then suggested:
Blower door test: Justin did have a blower door test done early on in his work on the house, but it was more a part of a sales pitch than a bona-fide test. He is certainly open to having one done now. A blower door test would help with two concerns: how much air leakage is taking place at the eaves; and how airtight is the 6-mil polyethylene installed in the highly irregular areas of his fieldstone crawlspace. So when this test is done, it’s important that the test be used to quantify airtightness but also to identify locations of air leakage. It would be great to get it done soon with good indoor-outdoor delta T and add in infrared imaging during the blower door test.
Ice dams: I asked Justin about ice dams because if heat loss (conductive and convective) at the eaves is resulting in ice damming, then dealing with the eaves becomes more important. Justin let us know that while the previous owners reported some problems, he has not noted any but agreed that keeping his eye on this is important as he finalizes his work plan on the house.
Complete the gutters: It’s particularly important to move the roof runoff away from the fieldstone foundation, and it looks as though on the front of the house the gutter and downspout does just that. A gutter on the front porch, particularly on the end adjacent to the fieldstone foundation, is important to add.
Install kick-out flashings: There appears to be more than one shed-roof-meets-sidewall location where kick-out flashings are needed, particularly at the left hand end of the front porch adjacent to the fieldstone foundation section.
Radon testing: Justin has used more than one radon kit (probably the alpha-tracker type, the most reliable), conducted in late summer and early spring, which showed 8 pCi/L in the basement and 0 on the first floor. But he has also purchased a continuous electronic monitoring unit (a Safety Siren Pro Series 3), which showed 6 pCi/L in the basement this past winter.
I have been running two Safety Siren Pro Series 3 units in my home off and on for more than 10 years, twice checking them against state of Vermont provided alpha tracker test kits run for at least three months in the winter. It’s important to check the electronic units over time because they can go wonky. I have found that levels correlate to cold weather and stack effect in my house: levels rise to 4 and above in the winter in my basement and move up and down with outdoor temperature (which I manage with an HRV dedicated to radon mitigation in the basement) until the spring, when levels move down to the 2 – 3 pCi/L range.
We don’t understand very well how airtightness correlates to radon levels, so it’s a good idea to keep your eye on radon levels as you make any space tighter, but particularly below-grade areas. And understand that any data you have on radon levels become part of the performance record of your home that must be disclosed if or when you sell your home.
Pin-type moisture content testing: I checked in with Justin on this because whenever you have wood framing in direct contact with masonry, it’s important to know how the moisture content of framing members in contact with masonry compares to the moisture content of framing that is not in contact. If temperature and relative humidity levels in your basement are stable, you can use an equivalent moisture content calculator like this one to get a sense of capillary action, or the lack thereof, where framing members have no capillary break with the foundation.
Capillary break: Does Justin need to jack up house to get a capillary break under his sill beams? If the beams are sound and the moisture content by weight is similar to other framing in the basement, probably not. However, as Justin changes the hygrothermal balance of the sill beams by air sealing and insulating around them, things can change. Insulating at the sill beams from the interior will make them colder and more sensitive to wetting. So, Justin should make every effort to keep them dry by managing surface water around his fieldstone foundation and consider insulating his above-grade foundation and sill beam from the exterior, using a water table detail to deal with the planar difference between the new exterior of that section of the wall and the clapboarded wall above. I recommend this because this approach warms the sill beam and leaves it open to inspection over time.
It’s just very cool that Justin has clearly been completely bitten and smitten by the building science bug, learning a ton — with quite a bit of that learning coming from GBA.