How can I stop in stop the infiltration of musty, humid air without tearing apart the wall of my historic home?
I live in a 100 year old house in New Jersey. Most of the time, the indoor air quality is fine, but on hot, humid summer days, especially after a rainstorm, the interior of the home is immediately overtaken by a musty, moldy –sometimes downright acrid–odor, and the humidity level jumps to about 80%. This come on very suddenly, and it vanishes just as quickly when the humidity level outside drops. I turn on my dehumidifier right away, which pulls gallons of water out of the air in several hours. This helps a bit, but is it not a real solution.
Some additional info: the house is clad in the original cedar clapboards, which are painted. The paint is peeling in many spots and a new paint job is planned. There is presumably no vapor barrier in the walls. In the late 70s, a previous owner pumped urea formaldehyde insulation into the walls. Where I have done extensive renovations (kitchen and baths), I have removed this stuff, which had settled and was crumbly/powdery, and reinsulated with closed cell spray foam. The windows are original — single glazed, beautiful but very leaky. I have also insulated the attic walls and underside of the roof deck with closed cell foam. It is now conditioned living space. We keep the interior of the house fairly cool in the summer–about 72 degrees. The humidity level and odor seem to be worst in the attic. I run a dehumidifier continuously in the basement, and it is always dry.
Any thoughts about what’s happening here? And what can be done — short of tearing apart my historic home and building a modern building envelope? I have considered insulating the walls that are not yet foamed with cellulose or injection foam, but I’m reluctant to do something that may worsen the situation.
Thanks in advance for your help!
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Apologies for the bad typing job!
Doug,
When it comes to musty odors, the first suspect is usually the basement. You didn't tell us much about your basement.
You should describe your home's foundation, and whether your foundation has any moisture problems.
Martin. Doug did say "I run a dehumidifier continuously in the basement, and it is always dry." I would want to know about the roof overhangs and gutters though. I would assume large overhangs on a house of that age.
Gentlemen,
Thank you for your replies. The house is a colonial revival "box" with a gable roof with 2 ft wide overhangs on all sides. There are 5" k-gutters at the eaves with leaf guards that go not catch all of the water in a major rainstorm. The downspouts and sump pump are piped directly to the street, though I'm sure the ground around the foundation is saturated much of the time due to the occasional gutter overflow. Excavating the foundation to waterproof it and install drain board and footing drains is not being considered because of the cost. I accept that the water & water vapor are coming in, and I try to deal with it on the inside. The sump pump does not actually run that often, and it smells pretty dry down there.
I neglected to mention that the walls are poured concrete and there is a French drain system at the perimeter.
Even though I'm a little worried about the basement, the location of the smell and highest humidity being in the attic seems like a good indication we should understand that better. It sounds like you have made the attic into a finished space with ccSPF between the new sloped ceiling and the roof deck, and you have also put ccSPF in new kneewalls. I assume there is an unfinished space between those new kneewalls and the eaves. Is the floor of that space insulated? What is the humidity and smell like in there?
What is the material and condition of the roofing?
Some possibilities include moisture getting in a roof leak, or moisture from the outside humidity coming in attic air leaks. So air sealing is a concern, between the finished attic conditioned space and the unconditioned attic space, as well as between the finished space and the outdoors.
Charlie,
The roof deck, gable end walls are insulated with ccSPF, as are the dormer walls and their roofs. The ceilings are vaulted (i.e. the ceiling is the roof in all areas). The kneewalls are not insulated, as they are inside the conditioned space. The attic floor, however, contains unfaced fiberglass (an attempt to minimize sound transmission between the attic and second floor rooms). I have considered the possibility that the roof could have a leak. I see no evidence of that, but I understand that ccSPF can make leaks hard to find. I shy away from that theory because the odor is fairly strong enough on the 1st and 2nd floors.
I have long suspected that poor air sealing is more the problem: that there is a big difference in vapor pressure between the cool, fairly dry inside and the hot, humid exterior causes vapor diffusion inward, and that the wall assembly has no ability to resist that. Once the moist air is inside, the ccSPF may trap it in the attic. (Does vapor-laden air tend to rise?) As for the odor, I wonder if the old urea-formaldehyde insulation is the source, or if mold has grown on the back side of the plaster & lath, which is cold in the summer and leads to condensation. Either way, couldn't water vapor passing through that environment pick up and carry the contaminants with it?
What do you think?
Thanks for the additional details. Re-reading your initial question, it seems like there's more of a correlation to outdoor heat and humidity than to rain. Is that clearly true, or can it be triggered by either? If it's outdoor heat and humidity, looking at outdoor dew point data would be the most relevant parameter. I see it's been peaking around 80 F in some parts of NJ recently.
I'm still unsure about whether to suspect the attic or just the walls in general, although you are convincing me to suspect the walls more strongly. A clue might be how the humidity and smell is in the spaces behind the knee walls.
If water vapor is getting through the walls, there are two ways it can travel. One is air leakage, and the other is vapor diffusion. Those are different mechanisms, both quite plausible. Urea foam does have higher vapor permeability than most types of foam, and there are also likely to be air leaks through it.
If the dew point outside is 75 F and the temperature inside is 72, any incoming air leaks will deposit condensation on the way in or soon thereafter. The resulting 100% humidity air will mix with your inside air and result in high humidity. Until the outdoor dew point drops substantially, e.g. below 60, the only way that moisture leaves is by condensing in your A/C coils. The spray foam in the attic doesn't trap it--the vapor drive is in the other direction across that foam anyway.
There's a grain of truth to the idea that water vapor, being lighter than air, rises, but my understanding is that that effect is pretty negligible compared to the diffusion and convection mixing inside a house.
So if your attic air is more humid than the air in other places, that's an indication that there are air leaks somewhere that allow outside air to get into the attic. The stack effect works in reverse in the summer--the inside air is heavy compared to the hotter outside air, and in falls from the attic to the basement where it oozes out cracks, bringing new humid outside air into crack near the top of the house.
As for how to find the problem more specifically, one possibility is a blower door test that would locate any air leaks, and allow you to consider ways of sealing them, as well as taking things apart near a few of them to look for mold. One challenge may be that the leaking air could take a convoluted path, and if might flow across the hidden side of the plaster before it gets to a hole where it leaks into the interior, and so it might drop its moisture somewhere ahead of where you would find the leak. A thermal camera might help you find spots where that warm outside air is blowing on the hidden surface of the plaster, by showing them as warm when that's happening, and perhaps as cold later as the water is evaporating. You could hire a professional with a blower door and a thermal camera, or you could rent or buy a thermal camera to do some sleuthing yourself.
But even if you don't actually find the spots where the mold is growing, if you stop the air leakage, you'll stop the supply of damp outside air to those mold colonies and they won't grow nearly as fast.
Charlie,
Thanks very much for your valuable input. I will certainly do what you recommend--thermal camera and blower door testing. Please tell me if you think these other moves make sense:
1) Dense pack the walls with cellulose, which would provide much-needed insulation but would perhaps also reduce the flow of damp outside air. (I understand that cellulose is not an air barrier.) The outside air might reach the dew point in the middle of the insulation, where it can do less harm (?) than it currently does, rather than at the back side of the plaster & lath. And maybe it would starve the existing mold of the moisture it needs.
2) Repaint the house. The house received a very good scrape-and-paint job 10 years ago, but the paint has since popped off is may spots, I'm guessing because of interior moisture diffusion to the exterior during the winter, esp. on the second floor where showers and sleeping people are generating water vapor. I'm thinking that a good paint job, while no vapor barrier, could be an impediment to moist outside air that wants to come in.
I'm eager to hear your thoughts. Thanks in advance!
It's possible that the dense pack cellulose would result in a better situation, because it would slightly retard air leakage and the fire retardant in it tends to regard mold growth, but there are likely other things you can do that would be more effective and at least as easy or perhaps easier.
The fresh paint would likely help retard inward vapor flux, but again, there are likely to be better options.
Charlie,
Thanks again for your insights. Please let me know if you have any other suggestions.
Doug,
The situation you describe is a head-scratcher -- a hard one to diagnose over the internet. Solving the puzzle will require diagnostic work on site.
Here's part of the puzzle: In hot, humid weather, it isn't unusual for humidity to find its way indoors. That happens in a lot of old houses. What's unusual in your case is the moldy, musty odor. The source of that odor needs to be pinpointed to solve this mystery.
Martin,
Thanks for your opinion. I've been puzzling over this one for a few years, so I'm glad to know I haven't missed something obvious. I'll be doing some forensic work with a thermal camera and moisture meter and will let you know if I find some answers. Thanks again!
RE dense pack cellulose in an old house, shortly ago Martin suggested to me to just 'live with' the shortcomings of an old house. We are zone 4a. My architect tells me not having a rainscreen is going to cause us problems. His suggestion is an Owens Corning product called rafter mate split in half and inserted against the house sheathing between the full 2x4s. Seems ingenious but I can find nothing regarding its effectiveness were dense pack cellulose to be applied against it. Comments welcome.
Sacie,
If you want to create an air gap in your stud bays -- presumably on the interior side of siding that is nailed to the studs without any sheathing -- and you are working from the interior, then you should read this article: Insulating Walls in an Old House With No Sheathing. The article suggests several ways to proceed.
Raft-R-Mate is an Owens Corning ventilation baffle intended for roofs. It is made of flimsy polystyrene, and will not be able to resist the pressures exerted by dense-packed cellulose.