# Could Poor Attic Ventilation be a cause of HIGH INDOOR Humidity?



## Windows on Wash (Aug 30, 2011)

If the air outside has a bunch of moisture dissolved in it, that will show in the interior. 

Run the AC for a few hours and it should dehumidify the air a bit if you are concerned. 

The humidity doesn't typically work from the top down in this situation. That being said, the attic floor should be as air sealed and insulated as you can get to. If you do that, you can help eliminate as much communication with the exterior and interior spaces.


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## Glanz (Mar 26, 2016)

Run the A/C in winter?


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## Bud9051 (Nov 11, 2015)

"Run the A/C in winter?" LOL, although it sounds crazy the ac is a great dehumidifier and should quickly bring the humidity level down.

@ Glanz, "but is this possible that poor attic ventilation would cause high INDOOR RH?" Not really. When ac is running and house is colder than the outside you will get a minimal air flow from attic to house, but not in the winter.

RH is a function of temperature and moisture content so you need both numbers to compare one location to another. Here is a calculator to help.
http://andrew.rsmas.miami.edu/bmcnoldy/Humidity.html

Also see post #21 this thread: http://www.diychatroom.com/f9/extremely-high-moisture-levels-attic-449226/index2/#post3741410

Sounds like you are doing all of the normal things to hold down the humidity. Read that other thread and play with the calculator to see if anything strikes a note.

Bud


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## Glanz (Mar 26, 2016)

What about running the heater vs air conditioner? Won't the heater dry the air and reduce indoor humidity? The house is cold... so to run the A/C would freeze us out.
When I tested the humidity around the house, all rooms were almost the same temp and same humidity 63Degrees and 64%Relative Humidity in the evening at 10pm at night. We did not have the heater running all day as we haven't started to use it yet but will if it will help with the indoor humidity. I noticed some gaps above the siding under the eaves so maybe air leakage is the cause of the high indoor humidity? So you don't believe that blocked attic soffit vents could cause indoor RA to be high? (i'm not saying the soffits are blocked because i haven't checked, i just need to know who to call out to help me figure this out, before indoor mold starts growing). Should I call a roofer? A siding person? A energy performance assessment contractor? A crawlspace person? btw crawlspace has fiberglass bats under subfloor, the crawlspace is 3feet big and easy to crawl around and i don't see any dampness on the soil, maybe a little bit in one small area (only about 3 inches of dampness next to foundation, no standing water anywhere).


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## Bud9051 (Nov 11, 2015)

Adding heat will change the number, but it will not remove any moisture. That is what an air conditioner or dehumidifier will do.

During the cooler season the indoor air leaks out the upper leaks and in the lower leaks, called stack effect and the amount of air exchange is typically huge, especially in a 1952 home vs a 2012 home. Back then energy was cheap so few air sealing measures were cost effective, even if they knew how important they are. Your home is, on average, replacing ALL of its inside air with outside air every 2 to 3 hours. That's 8 to 12 complete air changes every day. So, essentially, whatever moisture level is outside your home is what you will have inside, plus what the family activities and the crawlspace are adding.

Use the calculator to estimate the RH of your outside air once it enters your home and is warmed up to the house temperature. You said rainy season so sounds wet.

Bud


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## Glanz (Mar 26, 2016)

Okay, i'm beginning to understand but what can i do to reduce the outside moisture from coming inside? what type of contractor would i call? i don't want to have mold forming on my carpets or clothes (no mold yet) but the house was just flipped before we bought it (new laminate flooring, kitchen, bathrooms, painted etc) so i have no idea if the previous owner(s) had problems with mold forming with 65% indoor humidity and i don't want to find out for myself, i want to reduce the indoor humidity before mold happens. I'm doing all i can with using bathroom and kitchen fans, but would like to know who to call to stop the outside air from getting inside.


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## SeniorSitizen (Sep 10, 2012)

Quote:
*Could Poor Attic Ventilation be a cause of HIGH INDOOR Humidity?*

***************************************************************
Historically, that is not the root cause of high indoor humidity. The problem lies elsewhere.


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## Bud9051 (Nov 11, 2015)

Using exhaust fans works when the outside air is better than the inside. For every cubic foot of air you blow out a similar volume HAS TO come back in and it does so through any and all leaks it can find. The recommendations for using those fans doesn't apply to all homes in all climates at all times.

I suspect that a dehumidifier is going to become a permanent fixture in your home and that is just part of your climate. How much it has to run will vary with your air exchange and the outside weather. if you tackle the air sealing process you will reduce the amount of air you need to process. In the summer your ac will do the dehumidifying for you. Here's that link on air sealing. Start with the larger land easier to access leaks first.
https://www.energystar.gov/ia/partners/bldrs_lenders_raters/downloads/TBC_Guide_062507.pdf

Bud


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## carpdad (Oct 11, 2010)

Is around 64% bad? I do have a humidity meter and some days in summer went way above it. I'm in NJ so can't even guess what CA is like but as far as I know the only thing bad about humidity is it can promote mold and such and a short term highs don't matter very much - my guess. If the house smells musty, get a dehumifier. May need a several around the house. I run a cheap window fan all summer in bsmt and it helps but it's been relatively dry past few years.


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