# Attic moisture



## Carstonio (Jan 3, 2009)

We have problems with moisture on the inside of our attic every winter. I use weatherstrip tape to seal the cracks around the attic door and this doesn't seem to help. It's strange that the moisture collects on only the underside of the north-facing slope, while the south-facing slope remains dry. When our house was built, the builder laid roll insulation that appears to cover the soffits, so I'm concerned about adequate ventilation between the soffits and the ridge roof vent. At about three or four places in the house, mildew collects on the ceiling next to the outside wall, exactly the width of the joists. Some time ago I tried pulling the insulation away from the soffits, but I don't know if this mildew means there is still insulation there or if I pulled the insulation back too far -- the roof angle is so shallow that I cannot really see what I'm doing. I'm really out of my depth here and I would appreciate any suggestions.


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## Slyfox (Jun 13, 2008)

The southern side gets the winter sunshine and melts faster than the northern sections,
it could be and air flow problem, you need to make sure there is enough intake vents, which will be located in your eaves, check to make sure baffles where installed in between each rafter and make sure you have enough exhaust vents, which will be located up high near the ridge of the roof.

If this wetness occurs every winter than it's probably occurring in the summer months as well and you just have not noticed it,
this situation will progress and get worse as the years go by,
causing mildew, dry rot and possibly insects if not repaired.

If you can take some pictures both the interior of the attic and exterior of the roof it would make it easier to give suggestions.


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## Nestor_Kelebay (Jun 17, 2008)

I agree with everything Slyfox said, except the part about it being likely you'd have the same condensation on your roof in summer. And, of course, the statement that this situation will get worse with time.

What's happening is that warm, moist air from inside your house is rising up into your attic. It gets there through holes in the top plates of your interior walls that were drilled to run wires through to ceiling mounted light fixtures and ceiling fans. Also, even electrical wires running to switches and electrical outlets can be run through the ceiling, and that necessitates drilling holes in the top plates of interior walls to run those wires through.

Anyhow, the point here is that when warm air rises into a cold space (like your attic, then the moisture in that warm air condenses on the coldest surfaces in that attic.

And, to solve the problem, you need more attic VENTILATION. You should be able to provide more by pulling the insulation over the roof overhang on your house back so that air can get in the vents on the underside of the overhang.

The idea here is: Cold air comes in those vents on the underside of the overhang and warms up as a result of heat loss through your house's ceiling insulation. As that cold air warms up, it "sublimates" (similar to "evaporates" but it's solid ice that's evaporating, not a liquid) the frost in your attic. That warming air continues to rise until it ends up leaving your attic through the roof ridge vent. And, the escaping of that air results in new, cold, dry air being drawn in at the vents below the roof overhang.

That process continues 24/7 in the winter. Cold, dry outdoor air is warmed by heat loss through the ceiling insulation, and absorbs moisture as it warms. The resulting warmer wetter air escapes through the ridge vent, causing new cold air to be drawn in at the eves. That "convective air current" in the attic keeps the attic dry all winter.

I'd move the insulation in the attic so that it extended no further than the plane of the exterior surface of your outside walls. Having insulation in the overhang part of the roof does no good at all (cuz it just gets cold from both sides), and prevents that "convective air current" in your attic from developing.

What you should do is take the insulation off the overhang so that cold air can get in at the eves and can rise and escape through the ridge vent. If you see that the underside of the roof on the north side of the house dries up, then you've got sufficient ventilation in your attic.

The other way that moving the insulation will allow for better ventilation of the attic will be on windy days and nights. The notion that air will be drawn in at the eves and rise (due to warming) to the ridge vents and escape is kinda idealistic. Winter days and nights have as much wind as summer days and nights. By moving the insulation out of the over hangs, then on a windy day, the wind can blow through the attic, coming in along the eve on one side of the house and leaving through the eves on the opposite side of the house. This is ALSO effective attic ventilation.

Me thinks the problem is that the insulation in your overhangs is preventing proper ventilation of your attic space. You need to move that insulation to allow air flow through the vents on the undersides of the roof overhangs.

And, if doing that is not enough to prevent moisture from accumulating in the attic on the coldest nights of the year, you have to add more ventilation, perhaps by gable vents on attic end walls.

Think of it this way; once the warm moist air escapes through your ceiling, it's of no further use to you. Getting rid of it is better than trying to retain it cuz the moisture in it can cause condensation on the coldest surfaces in your attic. So, in my opinion, the more holes in your attic, the better. (That's cuz, the better the ventilation of your attic.)

PS:
Slyfox: Could you please explain why such moisture problems would occur in summer (when the underside of the roof is warmer than the interior of the house) and why the moisture problem would be expected to get worse if nothing is done to correct it. I agree with your diagnosis that the problem here is due to inadequate attic ventilation, but I cannot for the life of me understand why moisture problems would exist in summer, or why this problem would get worse in the winter if it's not addressed. Perhaps you can explain your reasoning for us?


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## Slyfox (Jun 13, 2008)

The temps in the attic will be higher than the exterior temps when there's poor ventilation, if it's a summer day and 80 degrees out side and a quick cloud cover/rain shower comes through, the exterior temps will drop numerous degrees in minutes, the interior will not change as quickly, thus condensation reaction occurs.

The difference in the attics interior temps and the exterior temps are not as great in the summer as in the winter, so the problem usually 'in some cases it is' is not as severe in the summer months, but it doe's still occur.

I have gone into attics before 'in the summer' and literally seen drizzling rain 'condensation built up' falling, of course that was an issue in which there was -0- ventilation, thus it doe's not apply to this situation, because this home owner has at least some ventilation.

Why will it get worse.
Take a piece of lumber and wet it, than let it dry out on it's own,
than repeat that process a few dozen times and watch the dis-coloring than deterioration process begin, apply that process to drywall and the problems occur even faster.

Setting moisture of any kind is bad, the more times it re-occurs the worse it is.


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## the roofing god (Aug 2, 2007)

check to see that you don`t have a gable vent close to a heat flue pipe,cold exterior air blowing against the pipe will cause condensation to form in that area,
unblock the soffit vents,
make sure your bathroom vents are vented to the exterior,and not dumping moisture in the attic

insulation prevents heat from getting above it,if that`s not working block any openings(from pipes,etc.)(if you are covering high hats/lights-make sure they are the insulated model(stamped IS),and add ,more UNFACED insulation to get above your recommended R-value
Ventilation removes the excess heat that gets past the insulation,which keeps it from meeting the cold roof sheathing ,and creating condensation,so having full ridge vent,and soffit vents is very important


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## crank.bait (Jan 24, 2009)

I just looked in my attic and have frost on North roof underside, entirely covered, not patches. I have small vents in West and East gable ends of attic, like maybe only 1'x1', but just have some small slits through outside siding. I have no overhang of roof, so there is no option to ventilate there. I have two pipes going through attic and out roof, one is water heater exhaust, the other is the plumbing vent. I have no ceiling lights, but ran coax cable through my air return ducts into attic, so there are a few holes there from interior of house, but I'd think that would pull air from attic into house not let house air go into attic. Any idea on what I should do? We run a whole house humidifier. I have no bathroom exhaust fan, as I found this frost because I went up there to look into adding a bathroom exhaust fan, as the bathroom currently doesn't have one. The roof does appear to have a ridge vent.


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## the roofing god (Aug 2, 2007)

I have no bathroom exhaust fan, as I found this frost because I went up there to look into adding a bathroom exhaust fan, as the bathroom currently doesn't have one.-crank bait

That is very likely your problem crank bait,the bathroom fan dumps warm moist air into the attic,and it`s freezing against the plywood----as far as the holes at attic floor,cold air can drop into the house,but heat rises-right into the attic-You should stuff insulation into any openings,and build an insulated cover for your attic opening also


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## crank.bait (Jan 24, 2009)

My quote says I have *NO* bathroom exhaust fan. So there is no fan putting moisture in the attic.


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## [email protected] (Nov 17, 2008)

For both crankbait and carstonio;

You need to check for both proper insulation and ventilation. 

I just worked on a house that had soffit vents installed but they were blocked by insulation. Causing both ice dams and attic condensation.

I don't have the time to type out all the info so here is a couple links to more.

http://roofingcontractorreview.com/Soffit-Vents-and-Attic-Ventilation.html

http://roofingcontractorreview.com/Roof-and-Attic-Ventilation.html


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## crank.bait (Jan 24, 2009)

My soffits only over hang by like 2", and I see no way there is any venting there. Aren't vents on the soffits on the underside like little slits in the soffit?


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## [email protected] (Nov 17, 2008)

"My soffits only over hang by like 2", and I see no way there is any venting there. Aren't vents on the soffits on the underside like little slits in the soffit? "


Yes. There are venting products to address that. Look up "smart vent" or "eave vent" .

Ed the Roofer has had success with the smart vent product. But I am a little hesitant about using that in a major ice dam area.


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## gma2rjc (Nov 21, 2008)

> At about three or four places in the house, mildew collects on the ceiling next to the outside wall, exactly the width of the joists.


Can you find out if the mildew goes all the way through the drywall in those areas? You may need to have those areas of drywall replaced if it does. One way to check if it's a live mold is to dip the end of a Q-tip in bleach. Touch the Q-tip to one area of the mildew/mold. If it changes colors, it's a live mold and needs to be taken care of.


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## Ed the Roofer (Jan 27, 2007)

[email protected] said:


> "My soffits only over hang by like 2", and I see no way there is any venting there. Aren't vents on the soffits on the underside like little slits in the soffit? "
> 
> 
> Yes. There are venting products to address that. Look up "smart vent" or "eave vent" .
> ...


I am not concerned about Ice Dams and their after affects, since the additional intake ventilation provided by the newly installed Smart Vent Product will cool down the attic and create a continuous airflow from eave to the ridge vents typically installed.

So far, since 2001 using the Smart Vent product on quite a few homes per year, there has not been one instance that I regretted it, especially regarding Ice Dams.

Ed


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## [email protected] (Nov 17, 2008)

"since the additional intake ventilation provided by the newly installed Smart Vent Product will cool down the attic and create a continuous airflow from eave to the ridge vents typically installed.
"

Makes sense to me.


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## Grumpy (Dec 12, 2003)

Carstonio said:


> We have problems with moisture on the inside of our attic every winter. I use weatherstrip tape to seal the cracks around the attic door and this doesn't seem to help. It's strange that the moisture collects on only the underside of the north-facing slope, while the south-facing slope remains dry. When our house was built, the builder laid roll insulation that appears to cover the soffits, so I'm concerned about adequate ventilation between the soffits and the ridge roof vent. At about three or four places in the house, mildew collects on the ceiling next to the outside wall, exactly the width of the joists. Some time ago I tried pulling the insulation away from the soffits, but I don't know if this mildew means there is still insulation there or if I pulled the insulation back too far -- the roof angle is so shallow that I cannot really see what I'm doing. I'm really out of my depth here and I would appreciate any suggestions.


Moisture in your attic is usually a result of an under ventilated and/or under insulated attic space. What is happening is that hot air holds moisture, when there is a lack of proper insulation the moisture migrates easily into the attic space. When there is a lack of proper ventilation there is nowhere for that warm moist air to go, therefore it condenses ont he framing, insulation and sheathing in the attic space. Once condensed, it will freeze due to the temprature.

The cure is usually pretty simple. Lowering of your humidifier(s) is the first step, although just a band aid, it is a major contributor. The average human family puts out 3-4 gallons of moisture in the air just by all around average daily life (cooking, bathing, prespiring, etc...). Next you need to assess your attic insulation. I know for my area the new construction code is R38. I also know most homes in my area built before the very recent code changes are about an R8 or 9, assuming the existing insulation still retains it's original R value. And finally you need a roofer/ventilation professional to assess your attic ventilation and make changes/improvements to allow the maximum amount of air to escape the attic.

Even though you do not have an overhang, an intake of fresh air can still be created, and would be ideal in any attic ventilation situation. 


As you say you are out of your depth, contact a licensed (if required by law) and certified roofing contractor who preferrably has experience in insulation as well. A good qualified roofer will understand the aspects of attic ventilation. If there isn't much attic space, blown in insulation is probably best and can be done from the outside if you don't mind the roofer putting a hole in it, or from the inside if no new holes need be added.


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