Attic humidity and mold

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Old 12-10-16, 08:58 AM
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Attic humidity and mold

So, we bought a 110 year old house about three years ago. The roof is about 8 years old now. It's about 1600 sqft with three peaks. It has a large Ridge vent on small peak and a small Ridge vent on largest peak. It has 4 gable windows and around 12 soffit vents in all. When we had out inspection the inspector didn't say anything bad about our attic.

About a month ago I went into the attic and noticed white mold growing throughout different points in the attic. I was Floored as I thought the attic is something I dint have to worry about. Upon reviewing it I noticed the bathroom fan had a 25 ft exuast hose that filled with water and ripped off the outlet. In otherwords it was blowing directly into the sttic. I've removed the vent and sealed the hole with foam board and spray foam. I'm planning on adding a vent in the wall but for now we use a window fan and dehumidifier while taking showers.

Since then I bought a hygrometer and have been watching it. It seemed fine until it got cold now it stays above 80% humidity and I get frost on the roofing nails.

I've also sealed around a gap in the furnace chimney. I've sealed shut one of the access doors with spray and fiberglass and I've built a box around the other one. I've also sealed up a few light fixtures I had access too. The problem is that there is old wood flooring throughout most of the attic as it use to be a two story house. They cut pieces and use blown in insulation.

Ive also added box fans to the gable windows blowing in and out. We run a dehumidifier in the living area and it stays around 40% there.

I know that the flooring will need to be ripped out and a vapor barrier and new insulation will need to be laid. Unfortunately, we do not have much money. My question is what can be done to help us in the short term? Will it just take awhile for the wood to dry out from the venting issue? Will adding a powervent to the gable vent help? Will adding fiberglass above the flooring help me?

Thanks for any response as I'm very worried about our roof as we do not have funds to get a new one.
 
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Old 12-10-16, 09:21 AM
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80% at what temperature? RH will seesaw with the temperature so when cold the RH will read higher.
The attic has no source of moisture of its own so the humidity up there is coming from outside or the house. Sealing off air leakage from the house is a first step, including all the way from the basement.

Use your hygrometer and take RH and temp readings at different locations plus the outside. Then use the calculator below to compare the dew point at each location, the lower the dew point the better. But the areas with high dew points are the likely source of the moisture in the attic.
Temperature, Dewpoint, and Relative Humidity Calculator

Then we will need to review your ventilation. Each vent will have a net free area rating (NFA) and the size of your attic floor will guide us as to how much and where that vent area needs to be.

Give us your location as well.
Once we get some RH readings we can advise where you need to take action.

Bud
 
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Old 12-10-16, 09:22 AM
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The humidity is likely coming from all over the house. Any air leakage from the home brings humid air into the colder attic. Take your 40% RH at 70F and introduce it into a cold attic that is 0F and the RH in the attic will shoot up to what you are seeing... 80% or more... it is like wringing out a sponge.

So the number one thing you can do is air seal everything. You have no vapor barrier on the ceiling so moisture can eventually migrate up... that's normal. To air seal, you could remove floor boards and look for more penetrations that are letting warm air in. Or maybe get an inspector to bring an IR detector so you can see the areas with the most heat loss, the concentrate your efforts there. Ventilation is good, bringing in fresh dry air will help keep the humidity down... but it will also speed heat loss, so it's a double edged sword. No adding fiberglass is not the answer.
 
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Old 12-10-16, 10:20 AM
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Thanks for responses. We live in mass. Just checked the readings and it's showing 75% RH in the attic at 32 degrees and 48% at 27 degrees outside. Currently 47% at 64 degrees in my kitchen. I'll take some other readings and post them.
 
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Old 12-10-16, 10:54 AM
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You can get a lot of information out of that calculator. Here's what I do.
Your outside air is 27 at 48% RH, that gives you a dew point of 9.9 rather dry.
Your inside air is at 47 at 64% RH that gives you a dew point of 43.
The attic is at 32 at 75% RH with a dew point of 25.

Since the dew points are a bit confusing to compare I use each with the new temp in the attic to see what that air would look like at the different temp.
Outside DP of 9.9 and attic temp of 32= 39% RH, much lower than what you have.
Inside DP of 43 at the attic temp of 32 = 154% RH, much higher than the attic and probably the primary source of your attic humidity. Of course an actual RH reading can't go above 100 but it is telling us that the inside air is very wet.

Of course some of the attic moisture could be from the past fan venting into that space but that should be drying out so continue taking readings.

Bud
 
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Old 12-10-16, 03:38 PM
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Your inside air is at 47 at 64% RH
I think you have those turned around.
 
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Old 12-10-16, 06:32 PM
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Thanks X. But I got the dew point correct so the conclusion remains the same. I sure need to work on how to easily explain the seesaw between temp and RH, even I get confused by what I say.

Bud
 
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Old 12-11-16, 07:40 AM
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So, the temperature dropped to 8 degrees overnight and now I have frost on my roof! 😩 the attic is 15 degrees with rh61% dp 3.96 . Outside is 8 44rh dp -9.44. Inside 64 degrees rh41 dp39.83. So, obviously the moisture is coming from inside the house.

My question is a vapor bsrrier usually necessary for use with blowing in insulation? Or should I just be looking for air leaks? Could I use a plastic vapor barrier over the top to get me through the winter. if I'm planning on replacing it all in the spring? I know your not supposed to but we have no money right now. What other options do I have?
 
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Old 12-11-16, 08:04 AM
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I think you could put a vapor barrier down as long as you cover it with a sufficient amount of cellulose. Generally vapor barriers are omitted on ceilings, at least in my area.

I would not obsess too much about the frost. As long as you have adequate ventilation in the attic , that frost will melt or sublimate and dry every day when the sun comes out and the attic warms up. Remember that your car gets frost on the windshield too, it's simply part of the nature of things when the temperature drops rapidly at night and crosses the dewpoint in your attic.
 
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Old 12-11-16, 09:55 AM
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As X said, a vapor barrier on top of the insulation would need more insulation added above it than there is below it to keep it warm. The easiest solution might be a powered exhaust fan in the attic pointed at one of the gable vents. It doesn't need a hole cut or fancy installation as any spill around the sides would help to circulate the air up there. But, being pointed at a gable vent would increase the ventilation and as you now know that outside air is very dry.

I hesitate to suggest a box fan as leaving one running in an attic may not be a safe option. Check out attic exhaust fans and get the smallest they offer. You could of course do a better install and really move a lot of air, but I think a limited amount is all you'll need and it will have less effect in terms of pulling more house air into the attic.

Bud

Note, also keep working on the inside humidity to get it as low as possible.
 

Last edited by Bud9051; 12-11-16 at 09:56 AM. Reason: addition
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Old 01-02-17, 08:01 AM
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Your vapor barrier should be on the insulation side facing down toward your second floor. If you simply have insulation blown in between the rafters so that the insulation material is touching the sheet rock of the second floor ceiling, that is a no-no and must be corrected. The vapor barrier stops water vapor from entering and passing through insulation. In other words, it stops warm air from meeting cold air which is what produces moisture. In the attic, it sounds like you have a situation. 1) get hyrogen peroxide and mix it with water in a spray bottle and spray the white stuff and see if it dissolves. You do not want anything growing. 2)Get a few boards up and see what is under the insulation as in a plastic sheet or paper, or aluminum backing of some kind If only the insulation is touching the ceiling sheetrock, correct that asap. Get a home energy audit to seal leaks. You do not want mold in the attic.
 
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