Frost in Attic What to do?

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Old 12-15-10, 11:26 AM
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Frost in Attic What to do?

Hi can someone help me figure out how to find a problem in my Attic? I have frost built up inside the attic roof plywood. I know its something to do with heat lost or getting up there. I wasn't sure untill now that it may be a leak. I have lots of vents, I also put two new vents on the peak of the house to create more air flow. The temp. in the attic is the same as the outside temp. So my question is how can I find out Where the problem is happening so I can correct it. Thanks
 
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Old 12-15-10, 12:31 PM
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A water leak is less likely to look like frost over an area. Possible, but less likely. I would look for an air leak somewhere under the area in question. Drop ceilings, recessed lights, plumbing channels, hot air ducts in the attic or inside walls below, attic hatch or side attic doors, any source of warm air from inside your home.

The problem is the air leaking out of your house carries with it a lot of moisture which condenses on the cold surfaces up there. Do you know what the relative humidity in your house is? Are you running a humidifier? The need to add humidity is another indication of overall air leakage. A tight home will exchange 1/3 of its air every hour. A leaky home will exchange it all every hour. That's a lot of moisture and energy.

Here is a great link on air sealing that might give you some hints. It opens slow, but worth the wait.
http://www.efficiencyvermont.com/ste...ide_062507.pdf

Bud
 
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Old 12-15-10, 12:45 PM
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I have know heat ducts in the attic. I do have an HRV at 50% and Humidfier on running at 40% with frost protection, only because I have hardwood floors in the house to keep my hardwood from cracking etc. If I don't have this humidity goes down to lik 29% which is dry. I have new windows and doors so the house is sealing up more and more which why I put the hrv in as well. But its only frosting up in the upper level attic Northside of the house...so has to be with something on that side of the house that is leaking I assume anyways I check that site out thanks. Please respond if you have any ideas
 
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Old 12-15-10, 02:49 PM
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Bud knows way more than me about insulation but my 1st thought was you need to add more insulation in the attic. The roof would be colder on the north side causing the frost from warm air escaping thru the ceiling.
 
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Old 12-15-10, 04:40 PM
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Sweating, ice, frost are always a ventilation or rh issue sounds like u have good ventilation try lowering the rh.
 
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Old 12-15-10, 05:09 PM
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If I lower the humidity any lower my house is going to be dry and my hardwood floors will crack so that can't happen plus my humidity is only between 38 and 40 percent. I am thinking of getting the blown insulation taken out and spray foam the top of the attic where the ceilings and vapour barrier meet but not sure how much that would cost but I am sure it will solve lots of problems..... what you think or maybe a cheaper answer
 
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Old 12-15-10, 08:41 PM
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If the outside temp is lower than around 40 then 40 percent is two high. Your floors won't crack at 30 %
 
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Old 12-16-10, 10:48 AM
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The key question to answer is, where is the moisture coming from? The likely source is that warm humid air from inside your home is leaking into the attic.

Are your bath fans vented to the outside? Have you checked to be sure they are not leaking? If the house was tight, you would not need to run the humidifier. Because so much air is leaking out, your furnace has to replace the heat and your humidifier has to replace the moisture. Stop/slow the air leakage and you heating costs will go down and your rh will go up without the humidifier.

If you read over the efficiency Vermont link above it will go in detail through the many places where air is leaking out AND where outside air is leaking in to replace it. Is there a bathroom below the problem area? Check the basement and look for holes in the floor above. Below tubs and showers, around chimneys, vent pipes, electrical and so on. A can of spray foam, some sheet metal can do a lot. Plus, if you add insulation, you may have to move it out of the way to air seal later. Air seal first.

Bud
 
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Old 12-16-10, 12:48 PM
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Ok Bud thanks. I don't have any bath underneath or basements. I have a split level so 4 levels. I don't have any fans running thru that attic .....The winter hear is cold......so humidity is really low outside right now. My hands and inside the house was dry and cracking so I know I didn't have enought humidity. My lower level is ok its just the upper attic so if my whole house was not seal correctly then I assume the lower and upper level would be frosted as well. So I am thinking its my thin vapour barrier they used in the 1970's that is not stopping the heat humidity . What you think Bud?

Thanks again
 
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Old 12-16-10, 05:37 PM
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Vapor transport is primarily associated with air leakage. The quantity of moisture that can move through sheetrock, wood, and other somewhat permeable material is minimal. If you have any amount of ventilation in the attic the small amount of moisture migrating through would be easily carried away.

Let's get specific.
1. Do you Have forced hot air heat?
2. Do your bathrooms, kitchen, and dryer have vents to the outside? Check to be sure they are working? Do you use them? And try to imagine where those vent pipes run.
3. Under your kitchen sink, bath vanity, tub, shower, there are numerous pipes going into the wall or floor cavities. Those locations are notorious for providing strange pathways up and into the attic.

Since the condensation and resulting frost will damage that plywood, if you are unable to locate the source of the moisture, check into having an energy auditor come in and run a pressure test. Along with an Infrared camera, they are typically well equipped to find your problem.

If you currently have fiberglass insulation in the walls and ceiling, note it does not stop air flow, thus holes drilled for wires and plumbing make your home look like swiss cheese.

Bud
 
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Old 12-17-10, 02:47 AM
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Ok bud understand. I have consider all of those possiablities. Neither of the vents go thru that attic. Only thing it can be I thinking or guessing is the light fixtures or the outside walls. but I will do some more investigating and see. I keep in touch Bud thanks again for you advice appreciate it.
 
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Old 12-17-10, 08:18 AM
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Just to note, an outside light fixture leaking air into the house or walls will not be carrying moisture with it. In fact, outside air is what dries out a moisture problem, at least during the winter.

Bud
 
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Old 12-17-10, 01:35 PM
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It sounds to me like you have a air movement problem. Check to see if your sofit vents are covered with your blown-in insulation. The reason you are getting frost is because the moist air is not escaping through your roof vents. The outside air is supposed to enter the attic through the sofit vents and circulate the moist air that rises to the attic from the house.

There are special baffels that are supposed be be placed between the rafters before the insulation is blown in. This keeps the vents from being covered when the insulation is blown in.
 
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Old 12-17-10, 03:54 PM
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I live in Southern Canada and to reiterate what airman said. 40% is too high if it is cold outside (ie. Northern Canada in December) even in a well sealed house (there is no way to perfectly seal a house). The humidifier manual will say as much. Wood will not crack at 30% as airman said. Certainly the localized nature of the problem suggests that there is a specific leak, but as I said, you will never totally eliminate all leaks and even a little air from a small leak at 40% humidity hitting minus 20C wood covered with shingles will form frost.
 
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Old 12-17-10, 08:01 PM
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As Bud said, air seal is #1, ventilation #2. Sounds like you have more exhaust vents now, than intake?
"Adding more attic ventilation is not the right solution. Additional roof vents allow more air to escape from the attic and that pulls more warm moist air from the house into the attic."
From: Energy Savers & Air Quality Services - Frost - Moisture

Gary
 
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Old 12-18-10, 09:12 AM
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ok everyone thanks for your advice. I am going to look into it now. I sure leaving my house between 35% 40% humidity is not going to hurt. Reason is when I keep it any lower depends on the temp. I do have frost protection hook up with this HVAC system as well which calculates the temp outside and inside which balances the HVAC and humidity inside. But have said this I agree that I have a leak up in the attic that can be sealed. Either thru spray foam or if I decide to Vapour Barrier up in the Attic this spring or more close to fall. I just have to decide which way I am going to go. I feel there also is enough ventilation, Reason is its suppose to be the same temperature as outside in your attic. Last year it wasn't like that it was warmer. This year I have to say that its perfect.As Bob was saying about leaks and stuff that I have to find them and reduce it. Then I won't have frost anymore to a certain point. So thanks for your advice everyone it was helpful and I know what I have to do. I will keep in touch what I decided to do and give you the results as I finish either this winter or coming summer. Thanks everyone again.

Craig
 

Last edited by Lats2008; 12-18-10 at 09:31 AM.
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Old 12-18-10, 04:18 PM
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Anxiously waiting to see the cause of Lats2008 attic frost. I am experiencing the same problem. Thought it was a ventilation problem but took care of that and still experiencing the same problem. I have duct work running thru my attic. Having an energy audit done on Monday to see if we can find leaks that could be causing the endless supply of moisture and where the source of the moisture is. It has been suggested that the source could be my basement foundation. Concrete block and the holes in block are not capped or covered. I don't have moisture seeping thru the floors or walls of the basement but when I monitor moisture with a hygrometer at the top of the foundation wall it measures 70 to 86% RH. I run a dehumidifier in my basement and it never turns off even in the dead of winter. I will post my results from energy audit but am looking for any ideas regarding the basement.
 
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Old 12-18-10, 06:03 PM
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Dehumidifiers are not for use in winter! High rh in winter is a lack of ventilation. You can seal every hole in the atic. But the moisture will still migrate through the wall and ceiling! Air sealing is going to make this worse because your house is all ready to tight
 
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Old 12-18-10, 07:00 PM
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The automatic humidistats I've seen have an adjustable set point, set to the high end they might call for 40% humidity at an 10F outside temperature, at the low end they might call for 10%, and you have to adjust (once) them to produce the desired humidity for your situation.
 
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Old 12-18-10, 08:46 PM
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Its not m basement. I did my wheeping tile, blue skine the outside, insulated it outside, and used a drainage board as well which solve and mositure thru my walls. Second i couldn't bass my concrete floor up cause my house was built on the water table and I thought putting in a sub pit would just run every hour plus my neighbours don't have one so I would be pumping them out as well. So since I never had leakage in my basement or flood I used Delta Floor on the concrete floor and level it and I have high ceilings so I use insulation 1inch and then OSB locking plywood 7x8 and it keeps the rest of the basement warm, and of coarse my walls are insulation with Roxos insulation and drywall. Maybe this help you when your planning.
 
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Old 12-18-10, 08:49 PM
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Also I plan to redue the attic with spray foam and battts insulation as or new vapour barrier as soon as I find the cause or where the problem is then fix it.
 
  #22  
Old 12-19-10, 05:01 AM
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Originally Posted by HRT60 View Post
Anxiously waiting to see the cause of Lats2008 attic frost. I am experiencing the same problem. Thought it was a ventilation problem but took care of that and still experiencing the same problem. I have duct work running thru my attic. Having an energy audit done on Monday to see if we can find leaks that could be causing the endless supply of moisture and where the source of the moisture is. It has been suggested that the source could be my basement foundation. Concrete block and the holes in block are not capped or covered. I don't have moisture seeping thru the floors or walls of the basement but when I monitor moisture with a hygrometer at the top of the foundation wall it measures 70 to 86% RH. I run a dehumidifier in my basement and it never turns off even in the dead of winter. I will post my results from energy audit but am looking for any ideas regarding the basement.
Even small imperfections in the air seal at the attic floor can admit large amounts of moisture, the openings around the perimeter of this attic access hatch were less than 1/64" wide:



Air infiltration into attics due to poor air sealing can cause condensation, sheathing damage and mold growth– Paragon Home Inspections Chicago/Northbrook/Buffalo Grove

you can also see condensed water vapor (frost) lower on the roof near the eaves.

With this in mind, it's easy to see how rising heated air in concrete masonry block walls with uninterrupted vertical cores can conduct large amounts of air into attics.
 
  #23  
Old 01-05-11, 05:06 PM
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Hrt60

As a follow up to my frost in attic condition. Had an energy audit. Found leaky ducts allowing warm air to escape into the attic causing the condensation. Had the ducts repaired and auditor coming back to perform duct blast test. Apparently the HVAC people who installed my system did a very poor job.
 
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Old 01-05-11, 07:35 PM
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Because minimum insulation on the ducts was R-7? This is close to your heat source, I can't understand why such insufficient R-values are required on the duct work.....

If using fiberglass, read this on the "biggest loser'; “How To” Buy/choose Fiberglass Insulation. - DIY Chatroom - DIY Home Improvement Forum

Gary
 
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