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Discussion Starter · #1 ·
First time poster, had a question about reducing humidity levels in my attic.

About 3 years ago, I had my attic and basement rim joists air sealed, and cellulose insulation blown into my attic to R49. Fast forward to now, and recently I noticed a 1-2 sq/ft area of my roof caving in. Went into the attic to inspect, and it doesn’t appear that the affected area is leaking (no water spots, insulation underneath area feels dry). Called roofer for estimate to repair, and the guy explained that excessive moisture in the attic could cause the sheathing to bow.

Went into the attic some days later to inspect the damaged sheathing for water leakage after a snow storm, and noticed light frost on the sheathing and nails. So, I put a weather meter in the attic to measure temperature and humidity levels. For the most part, temps/humidity match outside weather conditions +/- a couple degrees and humidity percentage. Inspected the bathroom fan (vented out of roof) and reinforced the insulated ductwork with foil tape around the connection point to the roof exhaust box.

My attic has gable, ridge, and power fan venting, but NO soffit venting.

There doesn’t appear to be widespread mold that I can observe; just a few dime size spots of white mold here and there.

Which finally brings me to my question: how can I reduce the humidity levels in my attic to acceptable levels? And, since the attic is supposedly air sealed, how much of an influence will the outside temp/humidity have on the attic space?

Right now, adding soffit vents isn’t an option. So, what can I do? Currently, I have a box fan running up there just to keep air flow moving.

Having an energy audit tomorrow, in the hopes that the blower door test may be able to identify spots in the attic floor that may have been missed during air sealing.
 

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Take a straw and put your finger over one end a suck on the other end, how's what working out for you.
No air in, no air out.
Unlikely that fan is going to do anything for you.
 
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It would be helpful for those willing to offer advice if you could describe the location or climate where you live.

I interpret what you’ve written as the attic floor is insulated and the roof sheathing is not, so this is a “cold” attic where the intent is for the temperature there to be similar to that outdoors. The typical setup in an attic like that is when the sun heats the air in the attic it rises and leaves the attic through ridge, gable or roof vents, to be replaced by colder air coming into the attic at the soffits. That natural flow of air from the bottom of the attic to the top takes any humidity that has been introduced into the attic from the living space with it. Without soffit vents you’re not getting an exchange of air in the attic, so excess humidity can become an issue. So if my interpretation of your situation is correct, then the standard solution to reducing humidity is the thing that you’ve said “isn’t an option”. I suppose that a big fan at one end of the attic pushing air out of the attic with (only) an inlet vent at the other end might produce the air exchange required. Would need to seal up all the other roof vents, though.

About 3 years ago, I had my attic and basement rim joists air sealed, and cellulose insulation blown into my attic to R49. <snip>
And, since the attic is supposedly air sealed, how much of an influence will the outside temp/humidity have on the attic space?
Maybe I’m just misinterpreting what you’ve asked here. When an attic is air sealed, leaks that allow living space air to get into the attic are sealed up. It has nothing to do with sealing the attic from the outdoors.

Chris
 

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Hi Grave and welcome to the forum. It's late so I'll jump right to a few questions.

What is controlling that fan, temp, RH, a switch?
Somewhere I saw the roofing industries guidance on high venting only and basically they just doubled the total NFA, which is a lot of vent area. IMO, not a recommended ventilation method.

Back to the fan. When running it is depressurizing the entire attic increasing the air leakage from house to attic and that could be your source of moisture.

What are the temp and RH readings inside your home and in your basement?

I assume the energy audit will include a blower door test and an infrared camera, best way to find air leakage.

Do you have forced air heating? Any ducts running through the attic or panned returns that create an air path into the attic.

Did they do any air sealing in the basement?

Enough for now.

Bud
 

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Discussion Starter · #5 ·
It would be helpful for those willing to offer advice if you could describe the location or climate where you live.
Pennsylvania. House is 1-story ranch, built in the early 60s.

I interpret what you’ve written as the attic floor is insulated and the roof sheathing is not, so this is a “cold” attic where the intent is for the temperature there to be similar to that outdoors.
That is correct.

So if my interpretation of your situation is correct, then the standard solution to reducing humidity is the thing that you’ve said “isn’t an option”.
Right now, soffit vents aren't really an option due to cost. I have vented, aluminum soffits installed on the house; problem is they appear as if they were installed over the original, solid soffit. If I understand the process correctly, it would require removing the gutters, fascia, metal soffit, cutting holes in, or removing, the original soffit, and then removing insulation around the soffit area and installing rafter baffles.

What I'm hoping to achieve is finding a (more) effective way to get air flowing through the attic with the existing systems I have in place.

I suppose that a big fan at one end of the attic pushing air out of the attic with (only) an inlet vent at the other end might produce the air exchange required. Would need to seal up all the other roof vents, though.
The box fan I placed upstairs is in front of the gable that typically allows air to flow into the attic due to wind direction. My thought process behind that was if I'm forcing air into the attic, it has to escape somewhere else, creating at current. Might not be optimal, but I imagine it's better than stagnant air at the very least.

Maybe I’m just misinterpreting what you’ve asked here. When an attic is air sealed, leaks that allow living space air to get into the attic are sealed up. It has nothing to do with sealing the attic from the outdoors.
When I had the cellulose installed, I had the insulators air seal the floor of the attic floor prior to blowing in the insulation. They also built a raised deck and access hatch and door made of green foam.

What is controlling that fan, temp, RH, a switch?
Attic fan is temp controlled only. I also placed a standard box fan upstairs to help keep the air circulating.

What are the temp and RH readings inside your home and in your basement?
Current temperatures at time of writing is:

Outside: 29°F / 87% humidity
Basement: 63°F / 54% humidity
Living Space: 68°F / 48% humidity
Attic: 32°F / 80% humidity

Do you have forced air heating? Any ducts running through the attic or panned returns that create an air path into the attic.
I have central heating/cooling, all ducts run through the basement. Besides that, there is a flex duct for the bathroom fan running out through the roof, a flue pipe for the water heater (which was sealed around), and what I think is a copper plumbing vent.

Did they do any air sealing in the basement?
The insulators used closed-cell poly foam to seal the rim joists.
 

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If I needed to improve air flow into such an attic I would install a couple of gable fans. If my roof didn't have a ridge vent I'd install them so one fan was an intake and the other an exhaust. Not sure since you do have a ridge vent, but it might be worth installing them both as intake. Maybe one of the pros can chime in on that.
 

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Can you post a picture of the soffit area?
As Bud mentioned by having a fan blowing out with no make up air coming in is going to create negative pressure in the attic which can suck air from inside the home.
Sounds like you have a general idea on what really needs to be done to correct this, just trying to figure out why you think the fachia would need to come off.
https://dciproducts.com/smartvent-attic-ventilation/
 
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I would suggest you monitor attic conditions for a longer period of time. On the one measurement set you provided, I don't see an issue --- attic conditions are effectively the same as outdoor.
 

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A lot of the air that ends up in the attic originates in the basement and IF unfinished there is often easy access to many of those leakage areas. If ceiling down there is covered with drywall, not so easy.

Using temperature to control the exhaust fan almost eliminates its exhaust function during cooler weather.

Off to play with your RH and temp readings.

Bud
 

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Disclaimer: I am neither a roofer nor a builder.

Right now, soffit vents aren't really an option due to cost. I have vented, aluminum soffits installed on the house; problem is they appear as if they were installed over the original, solid soffit. If I understand the process correctly, it would require removing the gutters, fascia, metal soffit, cutting holes in, or removing, the original soffit, and then removing insulation around the soffit area and installing rafter baffles.
That's quite possibly true. I know when I tried to get a piece of our vinyl soffit out that's what it looked like it would take.

What I'm hoping to achieve is finding a (more) effective way to get air flowing through the attic with the existing systems I have in place.
I don't think that's gonna happen.

Let me share with you a story about how I learned of the futility of trying to fight thermodynamics. I wanted my computer fan to blow air in, rather than out, so I could filter it. Problem was: Power supply was low and fan was high. The computer would run for a while, then shut down. I put a thermometer by the air exhaust and saw something that made no sense: The temperature would rise, then start falling, then the computer would shut down. It finally dawned on me that, despite the fact the new fan I'd put in was twice as powerful as the one it replaced, it could not overcome the force of the hot air from that PSU wanting to rise. Sure enough: As the computer ran, airflow out the bottom would steadily slow, then stop.

What's happening in your attic is the warmer air is rising to the cooler underside of the roof. Being cooler, and colder air being less able to hold moisture than warmer air, the moisture is condensing out of the air, onto the underside of your sheathing. Even if you manage to move some of it sideways by placing fans in both gables, one pushing and one pulling, it's still going to rise and there will still be warm, moist air cooling and the moisture condensing on the underside of your sheathing.

Never mind the electric bill from running fans like that essentially full time.

If you're seeing frost on the underside of the sheathing: It's wet. Really wet. When it gets wet it delaminates. When it delaminates it ends up with the structural integrity of cardboard. That's why it's sagging. (Btw: If it's sagging it already needs to be replaced. It's done.)

Oh yeah: And wetness in the attic can lead to mold. With all the stories that have been in the "news" I shouldn't have to tell you what that can mean.

When I bought our home the inspector I hired noted the previous owner had stuffed the soffits with insulation. The roof sheathing had mold and was beginning to delaminate. The very first thing I did, after we moved in, was get up there and spend hours painstakingly low-crawling into the corners and edges, pulling that stuff out. Still, when we had our roof redone three years ago they had to replace seven sections of sheathing--some so badly-rotted it would literally crumble in your hand.

In my inexpert opinion you're going to have to bite the bullet and fix your soffits. You should probably also get that sagging sheathing replaced before a heavy snowfall or somebody walking on the roof turns it into an emergency.
 

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For the most part, temps/humidity match outside weather conditions +/- a couple degrees and humidity percentage.temp/humidity have on the attic space?
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Of all the reading I've done on attic venting, the goal is to match outdoor conditions as closely as possible and you've done that by having gable and ridge venting as seen in your quote above. I'll stay tuned for all the interesting solutions.
 

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Discussion Starter · #12 · (Edited)
Can you post a picture of the soffit area?
As Bud mentioned by having a fan blowing out with no make up air coming in is going to create negative pressure in the attic which can suck air from inside the home.
Sounds like you have a general idea on what really needs to be done to correct this, just trying to figure out why you think the fachia would need to come off.
https://dciproducts.com/smartvent-attic-ventilation/
I've attached a picture of the soffit/fascia/gutter area. The whole construction is aluminum, and the lip at the bottom of the fascia folds over the edge of the soffit, which appears to hold it in place. Gutters are attached over the fascia. So, what it looks like to me is the gutters need to come off, then the fascia removed, then you can slide the soffit out.

I don't have a fan blowing out at the moment; but, what I do have is a regular box fan positioned in front of the west-facing gable (which gets wind blowing directly into it). My thought on doing this is to get more air into the attic (positive pressure). Since the air has to escape somewhere else, it has to travel across the attic to the ridge vent, attic fan, and/or gable vent on the east-facing wall.

This only a temporary solution, until I can resolve the elevated humidity issues.

A lot of the air that ends up in the attic originates in the basement and IF unfinished there is often easy access to many of those leakage areas. If ceiling down there is covered with drywall, not so easy.
The basement is unfinished, and I have easy access to everything down here (vents, wiring, joists, etc). Rim joist around the perimeter of the house has been sealed with close-cell poly.

When I bought our home the inspector I hired noted the previous owner had stuffed the soffits with insulation. The roof sheathing had mold and was beginning to delaminate. The very first thing I did, after we moved in, was get up there and spend hours painstakingly low-crawling into the corners and edges, pulling that stuff out. Still, when we had our roof redone three years ago they had to replace seven sections of sheathing--some so badly-rotted it would literally crumble in your hand.

In my inexpert opinion you're going to have to bite the bullet and fix your soffits. You should probably also get that sagging sheathing replaced before a heavy snowfall or somebody walking on the roof turns it into an emergency.
I have a pretty low-angle roof; getting to the soffit area (at least for me) is near impossible. But, I've only attempted it once. I may have to bite the bullet on the soffit if there is absolutely no other alternative. If so, then I only hope by cutting ventilation into the solid, original soffit of the house would give easier access to clean out the insulation and go from there.
 

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I have a pretty low-angle roof; getting to the soffit area (at least for me) is near impossible. But, I've only attempted it once. I may have to bite the bullet on the soffit if there is absolutely no other alternative. If so, then I only hope by cutting ventilation into the solid, original soffit of the house would give easier access to clean out the insulation and go from there.
We have a very low-angled roof, as well. To make it worse: It's a hip roof. That means there are corners that are impossible to reach from the inside. It is so low I have to be careful not to snag the back of my pants on the rafter ties going down the middle.

Nonetheless: It had to be done. I got up there with a couple small boards to move around and lay on, a small garden rake and a hockey stick. I pulled all the insulation stuffed into the soffits I could reach. Three years ago, when a new roof was put on, the roofing contractors removed some more when they replaced some of the sheathing.

That fall, when it cooled off, I got up there again, found that with a bit more effort I could reach more, and pulled some more out. Then I added 6-1/2 inches of fiberglass batt insulation across the entire area. Once again I found hockey sticks useful for allowing me to position it all the way into the edges--shy of the soffits, and the corners. I spent probably sixteen hours over three days up there doing that.

Doing these things is not a job for the faint of heart or for anybody not in top physical condition.

You have to have free airflow throughout the attic crawl space. It's the only way.
 

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Take a look at your plumbing, vent pipe, shower drain, and any other area where they removed wood to install the plumbing. Furnace exhaust as well. Use a smoke stick or other source of smoke and release it neat those openings to see where the smoke goes. Any electrical penetrations can be tested as well.

Normally we just seal everything, but testing gives you an idea as to their contribution.

From your numbers there is some moisture (not a lot) coming from the house into the attic.

The highest moisture level is the main house and at 48% RH it could go a little lower. Do you run a bathroom exhaust fan and keep it running for 15 – 20 minutes after showers? Do you do a lot of cooking and is there an exhaust fan in the kitchen?

Bud
 

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Discussion Starter · #17 · (Edited)
Doing these things is not a job for the faint of heart or for anybody not in top physical condition.

You have to have free airflow throughout the attic crawl space. It's the only way.
Everything I've been researching, and most who've I've consulted with, seem to agree. How to get it done will come down to either (my) time or (my) money.

It looks to me the soffit is vented similar to many aluminum soffits although paint may be obscuring air flow some.
They're vented soffits, but the don't vent anywhere. The original, solid soffit the house was built with is located about an inch or two above those aluminum soffits, so no intake air is reaching the attic that way.

The highest moisture level is the main house and at 48% RH it could go a little lower. Do you run a bathroom exhaust fan and keep it running for 15 – 20 minutes after showers? Do you do a lot of cooking and is there an exhaust fan in the kitchen?
Fan runs after showers. Maybe not that long; 5-10 minutes, maybe. Oven range doesn't vent to the outside; it just recirculates in the kitchen. Moisture in the living space doesn't seem too extreme; the RH may be at the max recommended level, but I never see condensation on window sills or anything of the such.

I should hear back about the energy audit next week. The auditor seems optimistic, but until I see the actual data, I won't know for certain.

I'm not understanding why he would need to question a pro sealing job that's 3 years old.
My initial concern was/is that some spots may have been missed during the air sealing process, and contributing to the moisture levels in the attic.
 

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They're vented soffits, but the don't vent anywhere. The original, solid soffit the house was built with is located about an inch or two above those aluminum soffits, so no intake air is reaching the attic that way.
So those vented soffits should be removed and replaced after the solid material is removed at least in part
 

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They're vented soffits, but the don't vent anywhere. The original, solid soffit the house was built with is located about an inch or two above those aluminum soffits, so no intake air is reaching the attic that way.
This I do not understand. Why would they have built it that way?

I'm wondering if they aren't vented, after all, like this



and, when they put the aluminum siding up, they were just careless as to where they put the vented soffit siding?

If you search on "soffit vents," you'll find solutions that may allow you to install them from the outside, w/o removing the aluminum. But, if the soffits are packed with insulation, you'd still have to clear that out.
 

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In houses like yours with no soffit vents, or with soffit vents clogged with insulation, I have been known to install typical roof vents, the ones that go near the ridge, on the bottom of the roof, just above the insulation line. It takes 15 minutes to install each one, they don't leak, and they get the job done.
 
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