Insulating walk-up attic in 1910 duplex in mixed-humid Climate Zone 4a
I have read *many* of your articles and comments (Martin Halliday, Dana Dorsett and Allison Bailes) about insulation, but still am having a couple of problems preventing me from getting moving on a project.
We just bought a 1910 1268 sq ft stucco balloon framed duplex (side by side), moved in at end of January last year. Despite no wall insulation, very old storm windows and badly installed fiberglass batt at the unfinished basement ceiling, the first floor is pretty comfortable for us. We have upgraded most rooms’ storm windows (and added one where there was none), and got a programmable thermostat (keep it at 67 in evening when home, let it fall to 56 overnight/when out, have it at 63 during morning hours when getting ready to go out). We do not plan to insulate the walls, because we didn’t use any air conditioning/don’t have a bathroom fan/have a sometimes wet basement, so we want to trust the plaster/stucco assembly to move moisture out.
But here’s the problem. There is a walk-up attic (not behind a knee wall, the door is on the full second floor), with floor boards almost all the way to the edge. (One floor board near one edge was pried up; there is about seven inches of space from edge of floor to eave walls or slant of roof). There is NO insulation in the attic. And you can see the sky in a few places in the walls in the attic. And the upstairs is *noticeably* colder than downstairs, you feel the difference 3/4 way up the stairs.
We have a more than 25-year-old natural gas boiler and 24-year-old roof (still sound), so there are a lot of big $$ demands coming soon.
We hired one insulation contractor, and I don’t trust him at all. He wanted to do open cell foam against sheathing in between attic joists (some 2 by 6, some 2 by 4), leave it without any ignition or thermal barrier, was only promising R13 in the smaller joist spots, and wanted to do closed-cell foam against the pine-plank party wall. Claimed there would be no problem with either humidity from the house or spotting leaks in roof after installation. Also said we would have to air seal ourselves where you can see the sky with can foam. Ignored the fact this doesn’t come close to R-38.
Even this would cost about $3,000, which would be a more than 10-year payback at the temps we keep the house now, especially if we didn’t get that much reduction in heating cost b/c it would only be R-20 or R-13. (If we get foster kids, we will be required to keep it much warmer, so our bills would be far higher than what we had last year)
I do have a just-shy-of 9 inch space between the lath of the ceiling below and the top of the floor boards. Because the place is small, we do have quite a few containers/boxes in attic (and a cedar closet there too). We had an electrical upgrade in attic, so I think we’re safe on knob and tube; no can lights on second floor.
Does anyone know how to find a consultant in the Washington DC area that can give us advice of what to do without being biased toward that company’s insulation product?
Is there a way to create an insulated hatch that would cover the top of the entire staircase, if we sought to insulate under the floorboards instead of against the roof sheathing? It is something like 30 feet long by 29 inches wide, if memory serves.
Or do we need to just wait until we redo the roof and do rigid foam under new shingles combined with foam against roof sheathing, and then drywall? If so, what is the proper approach for the party wall?
Can send pictures if you like, or more accurate measurements, but would be happy to pay for a consultant if I knew how to find one. Asked the city environmental dept., and they were no help, and local utility doesn’t sponsor this kind of thing in our jurisdiction.
I want to do the right thing for the planet (see avoiding a/c even in this climate!) and improve our comfort, but also don’t want to spend so much that it will take decades to recover the cost in lower natural gas bills.
Mara
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Replies
Hi Mara,
There is a lot in your question and I hope that a GBA user will come by who can recommend a knowledgeable professional in your area for you to work with. There are some articles here on GBA that will be informative, and helpful as you speak with contractors. I recommend the articles below, for starters.
All About Attics
Air Sealing an Attic
How to Insulate an attic floor
Creating a Conditioned Attic
How to build an Insulated Cathedral Ceiling
>"We do not plan to insulate the walls, because we didn’t use any air conditioning/don’t have a bathroom fan/have a sometimes wet basement, so we want to trust the plaster/stucco assembly to move moisture out."
That's not necessarily the right strategy. Zone 4A is a heating dominated climate- the low R-value and air leakage of open stud bays is still an energy and moisture problem, even if you don't use AC. It may or may not be safe to insulate those walls, but some amount of air sealing would be low risk, with a high return on energy use and comfort.
Pictures might help answer some of this:
Are the basement walls air sealed/ insulated? Are the stud bays open to the basement?
Does the balloon framing have top plates, or are the stud bays open to the attic? (They're usually open)?
Do the partition walls have top plates, or are they open to the joist bays in the attic floor?
Is the stucco on wood lath that's attached directly to the studs, with no sheathing layer?
Does the attic have soffit to ridge venting? If not, are the roof lines simple enough to use that strategy? Does the attic have any other venting?
>"Even this would cost about $3,000, which would be a more than 10-year payback at the temps we keep the house now, especially if we didn’t get that much reduction in heating cost b/c it would only be R-20 or R-13."
R13 is HUGE compared to R3-R4, which is about where you are with empty balloon framed walls. Air sealing may have as-great or greater effect on the fuel use & comfort as mere R value.
Are you willing to do any of the weatherization stuff DIY?
>"Also said we would have to air seal ourselves where you can see the sky with can foam."
Can foam breaks down under UV light. If you can see the sky that could be an issue. Is where you can see the sky, also a bulk moisture leak?
Dear Brian,
yes, I had read all those articles before writing my question!
Dear Dana,
Thanks so much for your reply. I will take some pictures when I get home. Basement walls are not insulated, they are cinderblocks. Do not know about studbay barrier if any between first floor and basement. The way the home inspector described it is that there was an open space in the walls all the way up, so I would think not?
I will check on the top plates, but I think not?
Stucco has a metal framework inside it (kind of a mesh), but not sure beyond that. How could I investigate that?
Attic is not vented anywhere I have seen, but would be happy to check to be sure, can you advise? There are three smallish square windows.
I am willing to do weatherization DIY depending on how technical it is. I'm guessing that pulling up the floorboards would be more than we could do.
There is no bulk moisture leak in attic (there is at times in basement). The places where you can see the sky are pretty small, most are smaller than a pencil, but I think there are one or two that are a little larger. Can take picture s of that, too.
>"Stucco has a metal framework inside it (kind of a mesh), but not sure beyond that. How could I investigate that?"
With balloon framing the studs rest on the foundation sill, and the bays are often open to the basement, with a gap between the foundation sill and subfloor you can peer up into. Sometimes that is blocked partially or fully by blocking or subfloor, sometimes there is a plank firestop between the floor joists blocking the view. If you find a stud bay where you look up into it, if you see planks on the outer wall instead of metal mesh or ~1.5" wide lath it means there is a plank sheathing layer, usually with a layer (or two) of tar paper on the exterior side (which wont be visible from the basement view) before the stucco layer. If it has metal mesh it's usually an indication that the stucco was added later, and the original house was probably sided with wood shingles/clapboard/shiplap or some other type.
If the attic has windows rather than grilles it probably doesn't have a gable venting scheme. Do those attic windows also have storm windows? (If not, they should.)
https://photos.app.goo.gl/G9mTut7Syuv9qJpa8
Attic and basement windows do not have storms, but just added a storm on first floor where there was none, and bought six other new storms. Three 25 inch windows. I was planning to do interior shrink wrap this winter on them.
Let me know if the link to all the photos I shot do not work. Some are close up enough it may be hard to tell what they are; that is brick behind plaster on party wall in attic; one of the holes in the floor is in the attic; one of the holes in the floor is in the kitchen, over the basement, through the 'subfloor' that is exposed there after we pulled up the carpet that was in the kitchen (!). I could not find any place where I could see down/up through balloon framing, but perhaps I needed to move some insulation against basement ceiling to do so? As I said above, the basement insulation is very badly done. But we are not too cold on the first floor, so that is not a this-year project. The attic is quite tall, 9 foot ceilings in most of it, and higher above stairwell.
The area covered by flooring is 15 feet wide and 40 feet long. Between the edge of the floorboards and an eave wall is 17 inches; between floorboard and the slant of the roof on the North (front) side is 8 inches.
One pipe is vented into the attic.
All the cracks to the outside are even smaller than I remembered, though it's hard to tell how big the one is that the bird got through! There is wire in that area, and I could not reach that far to pull it away to see how big the opening might be.
The very close up picture of the stucco shows the metal I was talking about. I do not think it was ever anything but stucco. There are a lot of houses this age that are stucco in this neighborhood.
There definitely are no grilles visible anywhere on soffits or on eaves on the outside of the house.
What I was trying to say about open stud bays between plaster and stucco is that it allows the moisture that is naturally in the house because of high humidity days/water in basement/steamy showers to escape out of the house. We have no moisture problems in the living areas (well, a little rust on one radiator in the full bath. But otherwise, no)
The stairwell opening, if we were trying to fashion a cap for it after insulating in the almost 9-inch space between bottom of floorboards and lath, is 29 inches wide by 11 feet long.
Thanks so much for your interest!
>"What I was trying to say about open stud bays between plaster and stucco is that it allows the moisture that is naturally in the house because of high humidity days/water in basement/steamy showers to escape out of the house."
Your thinking is intuitive to the casual observer, but actually backward. Rather than letting the steamy-day humidity out, the stucco and air leakage is letting the steamy outdoor humidity in. The basement is generally the coolest place in the house in summer- cooler than the dew point of the outdoor air much of the time, which is what gives it the "musty basement smell". When stucco takes on rain or dew moisture, it stores up quite a bit, which then gets released in intense bursts when the sun hits it, raising the humidity inside the wall cavities.
The fact that the house is air leaky helps purge moisture in winter, but it brings it in in summer- it's really uncontrolled. Controlling the air leakage does a huge amount for bringing it back under control, while also reducing the heating bill.
The original roof deck appears to have been skip-sheathing planks for mounting cedar or slate shingles (or tile), which is inherently highly ventilated. At some point a layer of plywood decking was put down over the skip sheathing so that asphalt shingle roofing (?) could be used, which lowers the air leakage but it's probably still pretty leaky. In your climate it would be relatively safe to install 2" of closed cell foam to the skip sheathing & plywood, and then fill the rest of the rafter cavities with compressed batts. That would be far short of code-minimum (R49), but if at the same time the exterior walls in the attic were insulated with a 1" shot of closed cell ( or a full fill of open cell) the air leakage out of the top of the house should go down considerably, and the upper floor would be warmer in winter/cooler in summer and the stuff in the attic would be better protected.
As long as at least 30% of the total R-value is the spray foam the fiber insulation won't get soggy over the winter, and with 2" of closed cell foam (R13-ish) you'd be good for up to R30 of fiber insulaition, even though it looks like you'd only get another R10 or so unless extending the rafter depths. So what if it's only R20-R25? Right now it's an air leaky sieve with only ~R2 of roof deck & roofing between the attic and the "Great Outdoors". It's easier in this case to air seal the roof deck and attic walls that it is to air seal the attic floor (without ripping it up, that is), and with the roof deck sealed it doesn't matter as much if the balloon framing and partition walls have top plates.
The plank covered party wall can be insulated & air sealed with 1.5" foil faced polyiso rigid foam covered with half-inch wallboard through-screwed to the planks (for fire protection. This is DIY- able for handy people if it's easy enough to bring 4' x 8' sheets of insulation & wallboard up.
The first floor probably stays warm in winter due to the excessive standby and disribution losses of the steam boiler. The basement is probably pretty warm in winter too(?). Cinder block walls can usually be safely insulated with 2.5" of rigid EPS foam (R10), held in place with 1x4 furring through-screwed to the foundation with 1x4 furring, with wallboard nailed to the furring. It may or may not be cheaper to go with 2" of closed cell spray foam treated with intumescent paint (for fire protection). Insulating and air sealing the basement keeps the basement drier in summer, and warmer in winter, rather than letting half or more of the standby losses of the boiler go directly outside.
If both the attic and basement are air sealed & insulated the temperature differences between the first and second floors even-out, even if the stucco walls can't be safely insulated. I'd need a site visit to make that call, or a peek at the inside of the wall cavites.
Is there a place in a closet or something where a 3" inspection hole could be drilled with a hole saw (for ease of repair) to see if there is any sheathing under the stucco?
Thanks, you've given us a lot of really actionable advice, I appreciate it! The sheets of polyiso and wallboard would be not hard to get up there, but I don't know how we'd reach the heights of the peak that are over that staircase!
The basement is not especially warm in winter, but it's not as cold as the attic. You know, basement like. :)
I don't know that the first floor is warmer than you would expect for where we have the thermostat set, but it feels like it is about right for that temperature. I find hot water radiators often overshoot a little naturally.
Would we need any intumescent paint over the closed cell foam against the roof decking before putting the batts below them? When you say compressed batts, do you mean rockwool, or high density fiberglass batts, or just buying thicker batts than fit in the remaining 4 inches of rafter (or in some places, the remaining 2 inches of rafter)?
By the way, my wife told me that the inspector told her there was an open cavity from basement to attic, so even though I didn't see where to look for the top plates, apparently he did, and found them lacking.
What would you use for those little cracks in eaves (which are wood shingles on the outside; only first and second floor are stucco)?
We really appreciate all the time you've spent thinking about our fixer upper house!!
>"I don't know that the first floor is warmer than you would expect for where we have the thermostat set, but it feels like it is about right for that temperature. I find hot water radiators often overshoot a little naturally."
It looked like a steam radiator valve to me in the picture, not pumped hot water.
If you have the jacket losses oversized cast iron boiler in the basement (and they are ALWAYS oversized) to heat it and the basement isn't fairly warm on the colder days it's an indication of massive air leakage into the basement.
If it's a pumped hot water system, not steam, the efficiency of a right-sized modulating condensing gas boiler could cut the fuel use in half, and stop the temperature overshoots. The oversized radiators were often painted silver to reduce their heat emittance to help with the overshoot/ hot-flash, but painting them any non-metallic color is enough to restore their full capacity, which allows it to deliver the heat at a much lower water temperature, and much higher comfort when used with a condensing boiler. Most systems can work at temperatures low enough that standard indoor latex paint can be used. The lower the water temp, the higher the condensing efficiency, and big high-volume rads like yours are usually a good match.
With a modulating condensing boiler that varies it's output temperature in response to the outdoor temperature (a control strategy called "outdoor reset"), once it's properly adjusted the radiators will always be warm, but only as warm as needed, and never hot, overshooting the setpoint.
>"Would we need any intumescent paint over the closed cell foam against the roof decking before putting the batts below them? When you say compressed batts, do you mean rockwool, or high density fiberglass batts, or just buying thicker batts than fit in the remaining 4 inches of rafter (or in some places, the remaining 2 inches of rafter)?"
The batts need to be thicker than the depth of the available space to work well. Rock wool or fiberglass is fine. It's still pretty easy to compress an 5.5" thick R20-R23 batt into 4" of space. Just don't leave any gaps or voids.
With half inch gypsum board over it you don't need the intumescent paint for fire protection.
>"What would you use for those little cracks in eaves (which are wood shingles on the outside; only first and second floor are stucco)?"
Is there full plank sheathing behind the shingles, or is that skip sheathing too?
Definitely hot water radiators, not steam. Perhaps they were steam at one point, I don't know, but there are two pipes for every radiator, & home inspector also confirmed. Also, most of our radiators are painted white, not metallic, and are warm, not hot to the touch.
We have one of those little box-like McLain Weil boilers, not a big cast iron one. The HVAC service guy we had said we should replace it with a high-efficiency condensing boiler because this one has to have the pilot light set up too high to stay on, and is at least 25 years old... and because if we didn't get a high-efficiency condensing boiler, he said we would have to reline the chimney, and that would cost $1000. He said the new boiler would cost $10,000. Not in the budget this year, not sure if we should prioritize new roof (including solar??) or new boiler after that. I really don't know how to characterize the basement temperature. Surely there is heat just coming off the water heater tank and the boiler, since there is no radiator down there, and it is not cold like you need a jacket down there. But it's been hot so long here, I can't really remember exactly what it was like in March and February! :)
Behind the shingles, depends on location! Right in the front over/under the windows, there is full planking and a little tarpaper on the inside above window -- no cracks to sky there. On the side, it's just skip sheathing.
Have a great weekend!