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  1. #1
    Tino Volpe's Avatar
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    Default High attic humidity

    Hi everyone I'm a newbie here. Looks like a great site. Seen some posts about this subject and I have a similar issue with high humidity in my attic that is driving me crazy. A couple of years ago had a new roof put on. The roof has 3 passive vents on the back of the house and the roofer added ridge vents. It's a HIP roof. I put in soffit vents all around. There was a little mold on the sheathing but I didn't think much of it. The bathroom fans were vented through the soffit. Well the mold situation exploded all over the attic. I had insurance coverage for it so had the mold removed, all the sheathing sealed, all the old insulation removed, then the attic was air sealed from the rest of the house. The bathroom fans were vented through the roof. Had a box put around the attic drop down stairs. New insulation blown in. I put a humidity/Temperature meter up there to monitor and installed an attic fan in one of the passive vents with humidity and temperature control. Well, the fan runs all the time because my other meter is showing the humidity at 90%! On cold dry days the humidity outside is registering at 30% and on the second floor in the bathroom at 45% yet the attic is registering 90% Where can this moisture be coming from. The fan doesn't seem to be doing anything. Then it runs the humidity doesn't decrease at all. I have to shut it down at the breaker cause it's costing me a fortune in electricity and not doing anything. So my questions are:
    1. Where can this moisture be coming from
    2. Is having ridge vents, soffit vents, passive vents and a fan somehow short circuiting the ventilation pattern. Should I block off the two passive vents to allow the fan to pull air through the soffits.

    One other thing I should add. The roofer, who I thought was a bit of a let's say not on the up and up, says he put it soffit ventilation that goes under the first row of shingles all the way around. When I look up there it looks like a 1 inch thick porus fiberglass that I suppose is letting air in around the edge of the roof. If that is true then wouldn't it pull moist air off the top of the gutters? Is that even possible? But I'm getting high humidity levels even on very dry days so I am totally stumped.

    Thanks for any help you can offer.

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  2. #2
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    Default Re: High attic humidity

    Impossible for me to determine from here. Sort of like trying to give you a haircut over the phone. You should hire a competent, experienced, highly rated home inspector to preform an evaluation for you in person.

    Joe Funderburk, CBO, CMI
    Alpha & Omega Home Inspections, LLC
    Serving SC & NC

  3. #3
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    Default Re: High attic humidity

    1. How is the house heated?
    2. Is there a vapour barrier installed in the attic floor?
    3. Could be a faulty meter/humidistat.
    4. Are you seeing any frost or moisture droplets on underside of roof sheathing?
    5. Is there a kitchen exhaust vent? If so where is it venting to?
    6. Are you sure bathroom exhausts are actually venting to exterior.
    7. Ideally exhausts in soffit can allow expelled moist air to be pulled back up into attic.
    8. Attic powered exhaust may be pulling warm air up into attic because it removing to much air.
    9. Ensure soffit vents are actually installed and functional.


  4. #4
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    Default Re: High attic humidity

    How old is the house? Is there a crawspace?

    If a man empties his purse into his head no one can take it away from him. An investment in knowledge always pays the best interest
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  5. #5
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    Default Re: High attic humidity

    Sounds like you have venting in the fascia not the soffit.
    From the attic interior you should see baffling at the bottom of the roof line.
    If no baffling then the new insulation may be blocking the ventilation.
    You might want to throw in some pictures.


  6. #6
    Tino Volpe's Avatar
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    Default Re: High attic humidity

    To answer some of your questions.

    House built in 1993
    No crawlspace, full basement.
    Oil baseboard heat
    Don't think there is a vapor barrier but have to confirm.
    Last time I went up there with the high reading did not see or feel any noticeable moisture.
    no kitchen exhaust
    Put in the soffits myself and their are not blocked.
    I'll try to grab some pictures to post

    Thanks


  7. #7
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    Default Re: High attic humidity

    Tino

    One thing it might behoove you to try is shutting off the powered attic exhaust fan and see what develops with the humidity reading of the attic area.

    Last edited by Raymond Wand; 01-31-2013 at 02:59 PM.

  8. #8
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    Default Re: High attic humidity

    Check that ALL plumbing vents are properly connected and exterior vented.

    Darren www.aboutthehouseinspections.com
    'Whizzing & pasting & pooting through the day (Ronnie helping Kenny helping burn his poots away!) (FZ)

  9. #9
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    Default Re: High attic humidity

    ok new roof i saw a post from previous that some one had a house with major frost in attic. turns out the furnace was suspose to be vented thru the roof but roofers had not brought it thru. do you have something venting into the attic and not all the way thru? this is something to consider too. also check where the power vent is and what kind of air is coming out dry wet or what? mositure is coming in somehow and staying where is it comeing in? attics them selves do not attract tons of mositure it is being vented from somewhere best to start checking for hidden vents or get someone with a infared camera and see what shows up


  10. #10
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    Default Re: High attic humidity

    Some good comments here.

    You say the house is sealed fro the attic. Was any pressure testing performed to confirm this?

    When people say they've done a thing, but don't test to prove its been done right, how do they know? They don't.

    With a blower door you can test how connected the house is to the attic.


  11. #11
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    Default Re: High attic humidity

    I have seen only one attic like this. We found the felt under shingles was put down starting at the peak. Mold was everywhere. When I looked it wasn't raining, and it was not perfectly obvious where the moisture was coming from.


  12. #12
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    Default Re: High attic humidity

    Thanks everyone. lots of good reponses. I'll try to answer everyone's questions.
    Furnace is brand new, has fresh air make up and vents through a old fashioned brick and clay liner chimmney.
    No plumbing in the attic other than the air handler for the central AC which has been shut off since September. Before they reinsulated the attic I went up there and made sure that all the ducts for the registers were tightly attached so no air could leak out from the AC system.
    When we did the roof and they peeled off the old shingles the original roof didn't even have felt underneath. I'll tell you this houose was built on the cheap!!
    The hmuidity doesn't change whether the powered roof fan is on or off. That is what's so puzzling. I would think it would make some difference!
    A pressure test was done before and after sealing and it passed.
    The plumbing vents were all working fine and properly connected unless the contractors broke one when they put in the bathroom venting through the roof. I'd have to dig through the blown in insulation to check that out.
    I wasn't home when they did the roof. I just assumed the felt was properly installed, as well as the rubber membrane for the ice dam.


  13. #13
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    Default Re: High attic humidity

    Quote Originally Posted by Tino Volpe View Post
    Thanks everyone. lots of good reponses. I'll try to answer everyone's questions.
    Furnace is brand new, has fresh air make up and vents through a old fashioned brick and clay liner chimmney.
    No plumbing in the attic other than the air handler for the central AC which has been shut off since September. Before they reinsulated the attic I went up there and made sure that all the ducts for the registers were tightly attached so no air could leak out from the AC system.


    A pressure test was done before and after sealing and it passed.
    The plumbing vents were all working fine and properly connected unless the contractors broke one when they put in the bathroom venting through the roof. I'd have to dig through the blown in insulation to check that out.
    I wasn't home when they did the roof. I just assumed the felt was properly installed, as well as the rubber membrane for the ice dam.
    AIR HANDLER IN THE ATTIC! That's probably the biggest issue. If the duct's aren't leaky you measured leakage? What was the duct leakage number? Friction fit duct? I bet it leaks faster than Grant took Richmond.

    What does "Passed" pressure test mean? How to express my confusion... If I asked for your height and weight and you told me "passing" does it make sense that's confusing? It is really frustrating when a subjective is disguised as a measurement, it avoids the question.

    You need a cfm50 number. That a measurement.


  14. #14
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    Default Re: High attic humidity

    Quote Originally Posted by Tino Volpe View Post
    To answer some of your questions.

    House built in 1993
    No crawlspace, full basement.
    Oil baseboard heat
    Don't think there is a vapor barrier but have to confirm.
    Last time I went up there with the high reading did not see or feel any noticeable moisture.
    no kitchen exhaust
    Put in the soffits myself and their are not blocked.
    I'll try to grab some pictures to post

    Thanks
    It is possible that your basement is leaking, the moisture evaporates and condenses in your attic.
    Where is your roof water discharging? How is your exterior grading? Have you camera scoped your perimeter draintile lately? Any visible suspect cracks in your foundation?


  15. #15
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    Default Re: High attic humidity

    The flexible ducts were just slip fit over the metal sleeves I used tie wraps and metallic seal tape to make sure they are on securely. I could try to seal all the registers below and see if that changes anything. But like I said how can the humidity in the house be 40% outside be 30% and the attic be 90%?
    What I meant by passed is that the insurance company and MASS save (in concert with National grid who handled this whole project) was happy with the results and said we were good to go and everyone was paid. I can look for the report (hope I have it) to get an actual number.


  16. #16
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    Default Re: High attic humidity

    I see part of your confusion. It's mistaking relative humidity for actual moisture. Makes it seem like moisture is magically growing.

    A little study of PSYCHROMETRIC curves should help you understand.


  17. #17
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    Default Re: High attic humidity

    Have you shut off the exhaust fan in the attic as suggested for 48-72 hours to see what the humidity level reads?


  18. #18
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    Default Re: High attic humidity

    It was mentioned that the attic was reinsulated. I would have a couple of questions about it. Is there good afir from the soffic to the attic. Are there chutes between every set of rafters and insulation did not get blown into the soffitt.

    Also there are to many different venting strategeties going on, soffit, fascia, ridge, turtle and powered vents.

    Is air actually going in the bottom and coming out the top. Is it being properly distributed. ITs like the sprinkler with all the little holes, are the holes plugged or short circuted.

    I think people make attic venting seem so complicated. It is realy very simple but it does start with the attic floor. The house needs to sealed and seperated from the attic and the attic floor needs to be well insulated. When this is done properly the house is no longer adding negative influences (moisutre, air pressure) and interfere with venting.

    When the house is sealed and insulated there is no need for a power vent. Unless the house is 100% sealed from the attic air is being pulled from the house. If there are air ducts or HVAC equipment there will be even more air exchange.

    The purpose of the venting is to expell excessive heat and moisture. Any moisture should be limited to outdoor humidity that is influenced by attic temps. It doesnt take much air flow to keep the humidity levels at a safe level.

    The myth is that attic venting is used to keep the attic air temp cool. Attic venting reduce exessive attic temps. It takes a whole lot of air flow to reduce the attic air temps close to outdoor air temps. I know most people think that the hot attic is causing the home to be hot but there are other factors that are the real cause. Most of the heat from the roof is radiated down to the insulation where is can penetrate the fiblerglass insulation thus heating the house. Also when the ac is running the air in the home is being cooled and pulling hot air in from the attic.

    Keep attic venting simple at 1sf of clear vent space per 300 SF of attic floor. Venting should be eveninly split between high and low. I rarely see vent chutes installed between all of the rafters. I think it is important and is recommended by BSC.


  19. #19
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    Default Re: High attic humidity

    From what I have experienced over the years is that ventilation in an attic space can be misleading. It may appear to have adequate venting but actually be vented wrong. There is one thing to take into consideration. Take for instance what happens when you experience a down draft in your furnace flue. This usually occurs when the stack is improperly installed as far as height is concerned. It very well may have to do with the position/location of the structure. Topography does play a role in venting. If the structure is located in a valley or hilly area, in a particular position, it may experience a consistant down flow of air that would restrict natural air flow out of the ridge vent. Air in, air out, it is as simple as that. Just something to consider. Good luck!


  20. #20

    Default Re: High attic humidity

    Tino

    you say the attic floor was air sealed.
    How was it air sealed.

    what are you using to read the humidity in various places? is it the same instrument? Make and model?
    What are the temps and RH for each of the locations.

    Pictures would go along way in helping to understand; the more the better.

    Mark Parlee
    The Building Consultant www.thebuildingconsultant.com
    “Real Solutions for Real Problems” EDI EIFS and Building Envelope

  21. #21
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    Default Re: High attic humidity

    Frankly I'd be looking at the clay lined masonry chimney, when if ever, have you had a Level II inspection of same? Any other fuel burning appliances, stoves, fireplaces, etc. besides the oil fired boiler? When was the boiler last serviced? What is the arrangement for domestic hot water?


  22. #22
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    Default Re: High attic humidity

    The chimney doesn't cut through the attic and the furnace is brand new, a Burhnam MPO with indirect hot water tank
    Found the inspection report, the blower door tests was 2100 before sealing and 1600 after.
    This mornming I saw forst on the roof sheathing in the attic
    When they sealed the attic they went and plugged every hole and crevice. I know it's bettyer because before they did that I had a definite updraft in the house. I could open the basement door a crack and feel a wind blowing on my face up from the basement. Now I get none of that. They also weatherstripped all the exterior doors and the sill on top of the foundation in the basement. This morning I went and covered all the AC registers with stretch and seal to see if that helps.
    Attached some pics of attic and temp/ humidity sensor showing reading in attic and on the second floor below the attic entrance. Hope this helps

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  23. #23
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    Default Re: High attic humidity

    Tino

    For the 3 rd time have you tried shutting off the attic exhaust fan? Its apparent its pulling warm moist air from somewhere. If you have frost then there is an air leak into the attic.


  24. #24

    Default Re: High attic humidity

    Quote Originally Posted by Mark Parlee View Post
    Tino


    what are you using to read the humidity in various places? is it the same instrument? Make and model?
    What are the temps and RH for each of the locations.
    What was the temp and RH outside?

    Mark Parlee
    The Building Consultant www.thebuildingconsultant.com
    “Real Solutions for Real Problems” EDI EIFS and Building Envelope

  25. #25
    Rod Corwin's Avatar
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    Default Re: High attic humidity

    Seeing as the chimney does not pass through the attic that rules that out but that still should have a stainless liner. If you are venting the bath vents via the soffit my guess is that the soffit vents are sucking bath exhaust right back into attic. Run those via flex duct to an end wall if possible.


  26. #26
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    Default Re: High attic humidity

    If the joints in the ductwork are not sealed at all joints there can be a significant amount of moisture entering the attic. At cold temperatures it does not take much moisture to reach 90% RH.


  27. #27
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    Default Re: High attic humidity

    My 1917 2 storey, wood frame has a hip roof with too short a ridge to even bother installing a vent. I do have a 10 inch diameter passive vent as close to the ridge as possible and a dormer whose window I close in winter (Boston). The large soffits have plenty of room to cut vents on all sides but I have yet to do it. Thin, original, 3 ply plywood ceilings are all that separates the 2nd level living space from the attic. No Plastic retarder and just foil faced fiberglass that is not everywhere and not tightly fit between the randomly spaced floor/ceiling joists. No vents in my bathrooms. Gas cooking and my wife and I cook and bathe a lot. Nice concrete floor in the unfinished basement. 3 rubble stone foundation walls and a brick wall at the walk-out rear. We have a Hermidifier brand humidifier at full throttle and still we have low humidity (29%rh now in basement). Also, we are on a small city lot with lots of trees and plants and shrubs next to and touching the foundation. And I can't stop my stubborn wife from watering almost every day. SO GO FIGURE.
    I DON'T HAVE OPTIMUM CONDITIONS but I will smell some mold, ONLY IN THE BASEMENT, in the summer if I don't have the BASEMENT dehumidifier running.
    Just 2 small window ac's that we only run about 10 days max in our very humid summer days.

    BOTTOM LINE: Some houses have mysterious lives. I have been in some unfinished, uninsulated attics in hot summer afternoons that were amazingly cool, and experienced other puzzling anomalies during inspections. But people don't believe how much water vapor can pass thru what seems to be barriers and retarders.

    Home & Condo Inspections in the Boston MA area by Certified & Licensed ASHI Inspector


  28. #28

    Default Re: High attic humidity

    I recently had a customer who was experiencing something very similar. They called due to water stains on the ceilings of their home thinking it was a roof leak. Turns out it was a very lint clogged dryer vent. The vent was disconnected behind the dryer in the laundry room wall. They never realized it, but there was hot humid air blowing up the cavity of wall and into the attic.


  29. #29
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    Default Re: High attic humidity

    Hi Tino

    You can't ventilate moisture problems out of your attic in the winter. In fact using ventilation enhancers like fans can actually make the problem worse.

    First, a few points so we are on the same page.

    The real number you need to look at is the absolute humidity and not the relative humidity. The capacity of air to "hold" water vapor is very dependent on temperature. The ability of air to hold "moisture" drops like a stone as we cool it. That 70 degree air at 40% RH in your living room will become 100% RH by cooling when you inject it into your attic and any cold surface it hits will get wet or frosted.

    Now you are thinking with all that ventilation going on why can't we get that wet or frosted timber to dry off. Simple. That cold air you are drawing in can't carry moisture worth s__t. It's COLD and already at a high RH.

    So the real answer to eliminating that moisture/frost problem in your attic is keeping all that nice warm moist air from your conditioned space from getting up there.

    Google "stack effect" to see why it's getting there and start tracking down all the little ways your nice living space air is going where you don't want it. Like all those holes the electrician drilled in the top plates of you walls and never used. Or them fancy pot lights you installed in the living room to highlight you fireplace mantle. Check every where the ceiling or walls are penetrated. Even from the basement where that pluming stack goes up through one of your interior walls. You got leakage.

    Also consider if you are inadvertently pressurizing your house; improperly set up HRV or outside air intake to the cold air return near the furnace or air distribution handler.

    Take that attic fan to the dump.

    Good luck

    Here's a neat table for you. In particular note how the relationship between the actual amount of "moisture" differs with temperature for any given RH. My apologies for it being in Celsius but that's the way we do things up here in Canukistan. I'm sure you can Google something similar up in Fahrenheit.

    Climate/humidity table

    Steve


  30. #30
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    Default Re: High attic humidity

    The Burnham MPO is a boiler line not a furnace. The description is not specific to know if mod or not, condensing options, etc. You made no mention of hving had clay lined masonary chimney inspected, relined, etc. and you indicate is in use for same. Frankly, I'd still be concerned at getting that Level II inspection and reviewing sizing, lining, integrity, etc. that set up regarding moisture migration source, and possible flue liner deterioration, etc. Esp since apparently wasn't relined or sizing checked when you had the newer boiler of unknown options, specifications, etc. installed recently (year or so ago IIRC).


  31. #31

    Default Re: High attic humidity

    The chimney effect of attics will literally suck up warm air from the house inside the attic from a poorly sealed and/or insulated hatch. The rest is as explained in this thread.


  32. #32
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    Default Re: High attic humidity

    There is no attic "chimney effect." An attic is just another leakage path, where carried moisture might cool to the dew point and condense. This repeats silly fear-mongering about attic ladders. An attic ladder should be just like any other exterior door, insulated and leak tight. Even better in tightness, because passed moisture is still at risk of condensation. Just buy a good one and install it air-tight about the ladder frame too. I am in the business of such ladders, but no one benefits from irrationality about driving pressures.

    My Insulation Math includes an early exercise in considering importance of leakage about an attic ladder.

    Irrational actions with stupid, bad ladders, all you find in stores, is discussed here:

    I have appealed to respected southface.org, to fix this horribly-misleading article:
    http://www.southface.org/factsheets/9atticaccess.pdf
    Path air flow is over-stated by times-ten, involving some miracle of physics.

    What is it about big organizations that make them unable to fix their messes, leaving messes as real embarrassments? Any web page can be edited. Links can be redirected. Documents can be fixed.

    There is this at US Department of Energy.

    I got to talk with a real person at Bonneville Power Administration in Vanvouver, WA, about this awful advice. Some supervisor huffed it would be fixed in some imminent new web contribution. I have little hope.

    Last edited by Phillip Norman; 02-10-2013 at 11:42 AM.

  33. #33

    Default Re: High attic humidity

    The movement of light warm air up thru a space and out a vent creates a vacuum which forces air up from low level eaves vents. When eaves vents are blocked with insulation or when not enough air comes in through the eaves, that creates an underpressure zone which tends to equalize itself by sucking air up from poorly sealed openings such as attic hatches, light fixtures etc. This is the chimney effect. I can't provide calculation to back this up though, I'm not that smart.


  34. #34
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    Default Re: High attic humidity

    Quote Originally Posted by Phillip Norman View Post
    There is no attic "chimney effect." An attic is just another leakage path, where carried moisture might cool to the dew point and condense. This repeats silly fear-mongering about attic ladders. An attic ladder should be just like any other exterior door, insulated and leak tight. Even better in tightness, because passed moisture is still at risk of condensation. Just buy a good one and install it air-tight about the ladder frame too. I am in the business of such ladders, but no one benefits from irrationality about driving pressures.

    My Insulation Math includes an early exercise in considering importance of leakage about an attic ladder.

    Irrational actions with stupid, bad ladders, all you find in stores, is discussed here:

    I have appealed to respected southface.org, to fix this horribly-misleading article:
    http://www.southface.org/factsheets/9atticaccess.pdf
    Path air flow is over-stated by times-ten, involving some miracle of physics.

    What is it about big organizations that make them unable to fix their messes, leaving messes as real embarrassments? Any web page can be edited. Links can be redirected. Documents can be fixed.

    There is this at US Department of Energy.

    I got to talk with a real person at Bonneville Power Administration in Vanvouver, WA, about this awful advice. Some supervisor huffed it would be fixed in some imminent new web contribution. I have little hope.
    I assume that Portland generally does not get very cold in the winter. I took a very brief look at you Insulation Math. From an insulation standpoint an attic stairway is not a very large heating loss. However, from a leakage standpoint most are very leaky, which significantly increases their inefficiency. Living in a relatively cold winter climate I can clearly see a correlation between attic moisture problems and attic stairways. I'm not sure why you do not think that an attic does not contribute to the chimney effect. It certainly does.


  35. #35
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    Default Re: High attic humidity

    Everyone is guessing, and getting you to run around in circles. WHY? Call a pro like these guys and get a test done. Bend Energy Efficiency Experts | Portland Energy Experts | Energy Savings Portland - Home Energy Audits - Greensavers USA


  36. #36
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    Default Re: High attic humidity

    Quote Originally Posted by Mark Reinmiller View Post
    I assume that Portland generally does not get very cold in the winter. I took a very brief look at you Insulation Math. From an insulation standpoint an attic stairway is not a very large heating loss. However, from a leakage standpoint most are very leaky, which significantly increases their inefficiency. Living in a relatively cold winter climate I can clearly see a correlation between attic moisture problems and attic stairways. I'm not sure why you do not think that an attic does not contribute to the chimney effect. It certainly does.
    I still say there is not a chimney effect at the attic floor. A heated column rises where surround is cooler. There is no column below the floor at elevated temperature, except in a real chimney with driven heat. There is nothing driving flow through gaps anywhere in the attic floor, but ordinary differential pressure. Roof high vents will suck more happily from a wind-driven soffit vent, than from moderated pressure inside the house.

    The solution is the same, however the problem is seen. Get stupid ladders out of our stores, selling anywhere only smart ladders that are gasketed and insulated. Seal all attic floor penetrations with care.


  37. #37
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    Default Re: High attic humidity

    Quote Originally Posted by Phillip Norman View Post
    I still say there is not a chimney effect at the attic floor. A heated column rises where surround is cooler. There is no column below the floor at elevated temperature, except in a real chimney with driven heat. There is nothing driving flow through gaps anywhere in the attic floor, but ordinary differential pressure. Roof high vents will suck more happily from a wind-driven soffit vent, than from moderated pressure inside the house.

    Maybe its a matter of wording. Air escaping through the ceiling will cause infiltration elsewhere. I do believe that wind and even thermal differences in an attic in window will increase exfiltration/infiltration.

    The solution is the same, however the problem is seen. Get stupid ladders out of our stores, selling anywhere only smart ladders that are gasketed and insulated. Seal all attic floor penetrations with care.
    I completely agree with you on this.


  38. #38
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    Default Re: High attic humidity

    Many good replies on the topic. You should be able to correct the issues with the comments posted. Although I didnt read every post, A couple questions I want to ask that may contribute to the moisture is... How many people in the household including animals? This also can lead to high levels of humidity. Are there a lot of pot lights throughout the home? Every ceiling penetration lets moist air into the attic if its not sealed properly. Make sure all duct work in the attic space is well insulated. Plumbing stack needs to be insulated. Get rid of powered vents. Vapor barrier is a must and it needs to be installed correctly. Put weather stripping on the attic hatch. Make sure the bathroom ducts are well insulated, not just buried under insulation. Homes normally have 3 types of venting they are... Soffit vents and ridge vent, or soffit vents and gable vents, or old school gable vents with a couple roof vents near the top. Take your pick, these options have proven effective as long as all the items have been dealt with. Frost on the underside of the roof is not a major issue, although some will say that it is. If it were the case every home in a northern climate would have moldy attics and they do not. The number one issue that I am finding right know is that with the large amounts of snow accumulation, attic vents have been blocked by snow. This is causing the frost to accumulte on the underside of roofs. Sound like your short circuiting your bathroom soffit vents with the power vent. Even without the power vent, the moist air being exhausted out the soffit is being pulled right back in.


  39. #39
    Join Date
    Apr 2014
    Location
    Connecticut
    Posts
    2

    Question Re: High attic humidity

    If you have no baffles than surly your soffit vents are blocked by the blown in insulation. Have you noticed any new mold growth?

    Even if you could stick a camera through the attic opening and just blind snap a few photos for us it may make all the difference in the world.

    - - - Updated - - -

    If you have no baffles than surly your soffit vents are blocked by the blown in insulation. Have you noticed any new mold growth?

    Even if you could stick a camera through the attic opening and just blind snap a few photos for us it may make all the difference in the world.


  40. #40
    Join Date
    Aug 2009
    Location
    rockport texas
    Posts
    132

    Default Re: High attic humidity

    Your ventilation is not working to many exhaust vents.You should only have one type of exhaust vent. The exhaust vents are "Short Circuited". Shut off the power vent, shut off the louvered vents, confirm the intake vents (soffit vents) are open and the problem will be solved.


  41. #41
    Andy Korovesis's Avatar
    Andy Korovesis Guest

    Default Re: High attic humidity

    Quote Originally Posted by Steve Zabarylo View Post
    Hi Tino

    You can't ventilate moisture problems out of your attic in the winter. In fact using ventilation enhancers like fans can actually make the problem worse.
    ...
    Now you are thinking with all that ventilation going on why can't we get that wet or frosted timber to dry off. Simple. That cold air you are drawing in can't carry moisture worth s__t. It's COLD and already at a high RH.

    So the real answer to eliminating that moisture/frost problem in your attic is keeping all that nice warm moist air from your conditioned space from getting up there.
    ...
    Take that attic fan to the dump.
    ...
    Steve

    Thanks, Steve! I live in the Chicago northwest suburbs, and with the very recent severe drops in temps here, my attic fan has been running through the night from about 9pm to about 8am for the last 3 days. This March I had my attic remediated due to mold problems, and since my fan doesn't kick in until RH is over 80%, I began to panic. The new insulation, R49, seemed to be all the way to the eves, with long baffles in every 2' space stapled to the roof decking.
    I went into the attic and pulled each bat under the blown in insulation back about a foot, in case soffit vents were blocked, and set the humidistat control on the fan to about 70% -- MISTAKE?? It ran all night again, but with the RH reaching only 73% (backing out the bats seemed to open up air flow).
    Your note about the fan just sucking in cold air and high RH from the outside woke me up!
    Should I just turn off the humidistat on the fan controller, and just let the fan work summers for high temps?

    Thanks!
    Andy


  42. #42
    Join Date
    Mar 2007
    Location
    Ormond Beach, Florida
    Posts
    26,245

    Default Re: High attic humidity

    Andy,

    The best solution is to permanently disconnect the powered attic fan (mounted on the roof and sucks attic air out to the outside - right?).

    Even during summer.

    During summer that fan is doing the same thing it is now -ssucking conditioned air from the living space, through the attic, to the outside ... which means that outside air is being sucked into the living space and you now have to pay to condition that air ... just to have that newly conditioned air sucked into the attic and back outside ... meaning new outside air is being sucked into the living space and you get to start all over again paying to condition that air so it can be sucked into the attic ...

    Unblock the attic vents and let the attic vent itself (with that fan left 'off').

    Jerry Peck, Construction / Litigation Consultant
    Construction Litigation Consultants, LLC ( www.ConstructionLitigationConsultants.com )
    www.AskCodeMan.com

  43. #43
    Andy Korovesis's Avatar
    Andy Korovesis Guest

    Default Re: High attic humidity

    Thanks, Jerry! I set the humidistat to OFF a few days ago and have been watching the weather station I have set up for the attic watch. Currently, it shows the attic temp is 47 degrees and humidity is 71%. Outside it's currently very sunny at 25 degrees with 71% humidity with a dew point of 17 degrees. Do I have a humidity problem based on these numbers, and is the attic in danger of mold again? I don't want to go thru another remediation process up there, after going thru it in April. This thing makes me jumpy and sick to my stomach with worry.
    Thanks again!
    Andy


  44. #44
    Andy Korovesis's Avatar
    Andy Korovesis Guest

    Default Re: High attic humidity

    Hi again, Jerry. I forgot to mention that I also went into the attic, and pulled all the bats back from the soffit areas about a foot. I can see light showing up thru the soffit vents now. With the bats and blown in insulation (Rr49), it seemed that the soffits may have been blocked, even with baffles installed by the insulation guys between every joist!
    Andy


  45. #45
    Matt Scicchitano's Avatar
    Matt Scicchitano Guest

    Default Re: High attic humidity

    Quote Originally Posted by Tino Volpe View Post
    Hi everyone I'm a newbie here. Looks like a great site. Seen some posts about this subject and I have a similar issue with high humidity in my attic that is driving me crazy. A couple of years ago had a new roof put on. The roof has 3 passive vents on the back of the house and the roofer added ridge vents. It's a HIP roof. I put in soffit vents all around. There was a little mold on the sheathing but I didn't think much of it. The bathroom fans were vented through the soffit. Well the mold situation exploded all over the attic. I had insurance coverage for it so had the mold removed, all the sheathing sealed, all the old insulation removed, then the attic was air sealed from the rest of the house. The bathroom fans were vented through the roof. Had a box put around the attic drop down stairs. New insulation blown in. I put a humidity/Temperature meter up there to monitor and installed an attic fan in one of the passive vents with humidity and temperature control. Well, the fan runs all the time because my other meter is showing the humidity at 90%! On cold dry days the humidity outside is registering at 30% and on the second floor in the bathroom at 45% yet the attic is registering 90% Where can this moisture be coming from. The fan doesn't seem to be doing anything. Then it runs the humidity doesn't decrease at all. I have to shut it down at the breaker cause it's costing me a fortune in electricity and not doing anything. So my questions are:
    1. Where can this moisture be coming from
    2. Is having ridge vents, soffit vents, passive vents and a fan somehow short circuiting the ventilation pattern. Should I block off the two passive vents to allow the fan to pull air through the soffits.

    One other thing I should add. The roofer, who I thought was a bit of a let's say not on the up and up, says he put it soffit ventilation that goes under the first row of shingles all the way around. When I look up there it looks like a 1 inch thick porus fiberglass that I suppose is letting air in around the edge of the roof. If that is true then wouldn't it pull moist air off the top of the gutters? Is that even possible? But I'm getting high humidity levels even on very dry days so I am totally stumped.

    Thanks for any help you can offer.
    I am having very similar issues as described in the thread. I'm curious as to whether it was ever determined by Tino what the cause was and what action was taken to cur the issue. I have started an additional post on this site to discuss my own attic.


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