Frost in Attic


Hi,
I have what may or may not be an issue with frost in my attic.
First a little background....
I have a bungalo built in the 50's that has a gable style roof. The home has plasterboard walls with what appears to be kraft paper for a vapor barrier. Original insulation is in the rafters (sawdust) as well as fiberglass bats on top (R12). 2 x 4 construction, as well as 2 x 4 for the rafters. The roof has 10 inch by 30 inch vents on the gables, as well as a few vents about 2 feet from the peak. The peak vents appear to be added at a later date. All vents have screening on them to keep out bugs and critters.
I'm currently doing a bathroom reno, gutted to the studs, replaced the sawdust with R12 fiberglass, installed vapor barrier with acoustic sealant around the top plates of the walls.
Three walls are drywalled as well as the roof. The bathroom vent has rigid metal pipe, insulated and sealed with tuck tape. The vent housing was also sealed with tuck tape and gaps around the housing have been sealed with expanding foam.
The lone wall without drywall is the tub alcove. That will be covered with durock, but I had to install the tub before I could do that.
Here is where my problem begins....
I was installing the supply pipes for the tub and I noticed a wet spot between the studs on the open wall. At first, I thought a pipe may be leaking, but on further inspection, I saw a leak working it's way through the acoustic sealant where the vapor barrier was starting to lift.
I thought to myself, holy crap, my roof is leaking.... So I went to where my attic hatch is (not in the bathroom), popped it open and noticed that the underside of the roof had a light layer of frost which was melting and falling onto the insulation.
The weather has warmed up here considerably for January and recently rose from a -25 C high to around 0 C. There was no wind on the day that this happened and the leak has now dried up on it's own. The time frame for all of this was about 5 days.
I checked the attic last night and there is still frost on the underside of the roof, but the melting has stopped, and no new frost has formed.
I suspect that this may be normal for this type of house and I probably wouldn't have a leak if the wall covering was in place, and I don't see any signs of roof leakage anywhere else in the home. I've been in the house for 9 years.
I'm thinking I may need to upgrade the venting in the attic. The front of the house has a oversize eave that is stucco'd. This is common on all the houses of my style in this neighborhood. This eave does not have venting and I suspect the gable vents and newer roof aren't doing the job.
Any opinions on how to handle this? Perhaps I'm being paranoid and I should just leave things for now.
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It sounds as though there is moisture bulding up in the attic and that it is not adequately vented to the outside. Is there a vapor barrier under the insulation in the attic to keep the moisture from the house from getting into the attic? If not, some sort of moisture barrier paint (someone else may know if this exists) on all the ceilings may reduce moisture getting into the attic. Otherwise, you will need to increase the ventilation in the attic. By the way, what you call Tuck tape is commonly called DUCT Tape as it is used (supposedly) to seal seams in heating/cooling air ducts. You sound as though you are located somewhat north of the Mason-Dixon line, maybe in Canada. If you don't do anything, htere is a chance that mold will form, altho if that hasn't happened in 50 years, you may be just fine.
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wrote:

Sounds like my parent's home. Solution was to replace the plywood soffit with perforated vynil and adding a ridge vent.
JImmie
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hr(bob) snipped-for-privacy@att.net wrote:

Where I live, standard "Duct Tape" is NOT approved for ducts. It just doesn't last.
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wrote:

TUCK tape - red tape used to seal holes, etc in vapour barrier, etc. Feels like packing tape... very thin plastic.
DUCT tape - this is FOIL tape, made of METAL that is used on ducts to seal leaks and joints.
DUCK tape - grey cloth tape, used in wet applications like sealing a hole in a tarp.
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wrote:

It sounds as though there is moisture bulding up in the attic and that it is not adequately vented to the outside. Is there a vapor barrier under the insulation in the attic to keep the moisture from the house from getting into the attic? If not, some sort of moisture barrier paint (someone else may know if this exists) on all the ceilings may reduce moisture getting into the attic. Otherwise, you will need to increase the ventilation in the attic. By the way, what you call Tuck tape is commonly called DUCT Tape as it is used (supposedly) to seal seams in heating/cooling air ducts. You sound as though you are located somewhat north of the Mason-Dixon line, maybe in Canada. If you don't do anything, htere is a chance that mold will form, altho if that hasn't happened in 50 years, you may be just fine.
The DUCT tape you refer to is not what I'm using.
It is referred to as building wrap tape. It uses the brand names such as "Tuck" tape or "Tyvek"
See example with this link...
http://www.can-save.ca/Building-Envelopes/tuck-tape.html
And yes, I am north of the 49th parallel. Winnipeg, Manitoba. Unusually warm for January this year.
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On Wed, 20 Jan 2010 15:22:16 -0600, Iowna Uass wrote:

In super insulated homes you do NOT put a vapor barrier in the ceiling. The moisture needs an outlet and that is through the ceiling. If you do put a vapor barrier in the ceiling you will get moldy ceilings. You need to increase the ventilation in the attic.
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Michael Dobony wrote:

I thought they used air-air heat exchangers for this.
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That sounded incorrect for today's construction. So found this explanation.
In the old days, in severe cold climates, when attics were poorly insulated it was okay to omit a ceiling plastic vapor barrier. The heat loss from the house warmed the attic sufficiently to allow attic ventilation to remove moisture from the attic. Cold outside air was brought into the attic and warmed up by the escaping heat loss giving this air the capacity to pick up moisture. Moisture in the attic was then picked up and vented to the exterior. The approach worked great until we added large quantities of attic insulation. With the added insulation the attic stayed cold and the ventilating outside air stayed cold unable to effectively remove attic moisture. Hence the need to reduce moisture flow into the attic and the need for a vapor barrier.
Noticing that several operative words are; 'old days', 'omit vapour barrier', 'vented to the exterior' and 'reduce moisture flow into the attic and the need for a vapor barrier'.
Reading sources such as 'Canadian Frame House Construction' etc. (even my old one covers vapour barriers and attic venting), possibly available at library should also illustrate. .
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Iowna Uass wrote:

Yup. Insufficient attic ventilation would be my guess.
Rule of thumb: You can't have too much soffit venting.
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Minimum attic venting for our climate here, which sounds similar, is 0.3 percent of the floor area arranged to provide cross ventilation.
In other words a minimum of 3 sq feet of ventilation per 1000 sq feet of attic floor area. We added much more than that and check at least a couple of times annually.
Frost, melting and the consequent dampness could be serious. Rotten roofing, damp ineffective insulation, possible mould.
Franky we would consider such a problem affecting the basic house structure and possibly the healthiness of the air within the structure, more important than refurbishing the bathroom!
Suggest you temporarily add some power ventilation ASAP. Then investigate permanent solution; also why and where is the moisture that is causing the frost coming from. Sounds serious! And new roofs are expensive.
BTW some houses have a continuous ventilation strip along each soffit, also if necessary end gable vents and/or ridge vents. We've added extra vents along our soffits and also have gable end vents. That 'kraft paper' vapour barrier doesn't sound too effective either! Have read that at a pinch the use of impermeable 'oil paint' on the ceilings can provide something of a vapour barrier.
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IT IS A BIG ISSUE. MOLD. ROT. DETERIORATION OF THE LOAD BEARING MEMBERS.

stuff snipped ......

I'd say vent the eaves. And have a pro come and look at it and give you a free estimate and pick his brain to see if it is a DIY thing or a major job. This is not a small item that I would personally leave to molder.
Steve
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Iowna Uass wrote:

Are the eaves not accessible from the attic? If they are, it should not be a big job to add vents. I just cut retangular holes into my eaves and snapped metal vents into them.
If eave vents are not possible, adding additional end vents as low down in the corners as you can will help get the convection airflow moving.
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On Wed, 20 Jan 2010 12:27:35 -0800, Steve B wrote:

Great answer.
Let me recap.
Screem at the person about something you don't know what your talking about.
Snip the part that confuses you.
Finish with, pick the brain of a professional.
In total, Another dipshit that doesn't have a clue.
There are too many here like you already.
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What is happening has been happening awhile so before panicking look at the color and condition of all the wood, if venting is bad it will be black and even areas of mold and maybe rot, if its brown venting is probably fine since it goes black fast with inadequate venting. Frost can happen it certain weather conditions, its normal. Maybe venting is fine but somewhere alot of warm air is escaping into the attic. How thick it total insulation, do you have R12 on top of 4" so its maybe R27 total? R 40 would be a minimum. Fiberglass batts loose effectiveness as its get real cold and the R12 you put in is compressing to less, measure what you have now total and figure R 3.75" for what you have and add more unfaced insulation, the vapor barrier should only be above the ceiling on the attic floor.
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I had a friend who's a contractor look at the situation, and he informed me that it is common for some frosting to occur in this climate, especially when the temperature rises from -25 C to +2 C in a day. The situation could be improved by some vents along the lower part of the gable to increase the amount of attic area with ventilation. He said not to panic and I would've never noticed the alleged problem if I wasn't currently renovating the bathroom. He also recommended that I add an extra layer of R12 to the exsiting layer of insulation, add u-channels to the rafters where the insulation meets the roof on the side of the house that has soffit vents to keep the insulation away from the roof and allow breathing.\
He also said to take some pictures of the the attic and poke my head up every few weeks and take some more. Compare the pictures to see variations in frosting (if any).
Thanks to all who replied.
Thanks
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I had a leak last week on my ceiling, went up into the attic and discovered little piles of snow on top of the insulation under each air vent. This was after a rare (where I live) blizzard. This is the first time this happened since we moved in 15 years ago.

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news wrote:

Hang a yard sale cooking pot under each vent?
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Got Attic Mold? Lets Talk Energy Conservation! By Mark D. Tyrol, P.E., Battic Door Energy Conservation Products
It happens to countless homeowners around the end of the year you make the annual visit to your attic to collect the holiday decorations and what do you find? Spots and blotches covering the bottom of the roof sheathing. Worse yet it turns out to be attic mold!
What does energy conservation have to do with mold in the attic? Well if you take a step back and consider how the house behaves as system, they are often directly related.
Building science experts have long been using the house as a system approach to diagnose the cause and origin of building defects.
For example, ice dams. These are often caused by warm air seeping into the attic which causes the snow and ice on the roof to melt. The water drains to the edge of the roof (which is colder than the rest of the roof because it is an overhang and not warmed by the attic), freezes and creates an ice dam. As this process is repeated daily, the ice dam grows larger. Eventually water is forced under a shingle where it can seep into the house.
Understanding how the house behaves as a system and the various causes and effects is necessary to diagnose most building related problems.
But how about that attic mold? How did it get there?
Mold requires chronic moisture to form and to thrive, so source(s) of moisture must be present. Possibly the moisture came from outdoors. The roof is newer and a quick check of the roof shows no obvious damage or leaks.
Possibly the moisture came from indoors. During the heating season, the interior of the house frequently has high moisture levels, especially bathrooms and kitchens. A quick check shows that all bathroom fans, kitchen vents, etc. are properly ducted completely outdoors and not into the attic. The amount of insulation looks good and the attic is well ventilated.
Dont give up you are almost there! Remember the house as a system? You know that warm, moist air is in the house, but how is it getting into the attic?
By air leaks! Air leaks are the leading source of energy loss in most houses, and a frequent source of chronic moisture that can cause attic mold. Most homeowners are well aware of air leaks around windows and doors (especially old ones), but many overlook the numerous gaps leading directly into the attic!
Have a look around the attic and you may find large gaps around recessed lights and fans, holes where wires or pipes are installed, even large gaps around the chimney. And dont overlook the whole house fan and especially the folding attic stair - a big, uninsulated hole in your ceiling that is often overlooked!
These gaps can add up to a large hole that allows warm, moist air from the house to flow right into the cold attic. The warm moist air condenses on the cold roof sheathing, creating chronically damp conditions that can lead to attic mold growth. And the energy loss it can be like leaving a window open all winter long!
Seal these air leaks and you stop a significant moisture source. And just think of all the energy you can save and the cold drafts you can stop!
Mark D. Tyrol is a Professional Engineer specializing in cause and origin of construction defects. He developed several residential energy conservation products including an attic stair cover and a fireplace draftstopper. To learn more visit www.batticdoor.com
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