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Old 01-05-2009, 10:56 AM   #1
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Recently Topped Up Attic with Blown Insulation...Now I have Frost/Condensation


Hi everyone,

I recently had moisture issues in my attic that seemed to be caused by warm air escaping from my home into the attic and not being vented out properly.

I have recently gotten my attic toped up with blown-in insulation (6 inches) which now gives me an R-value of about 50.

Problem now is that there is some frost build-up on the attic roof and the nails look like little snowballs.

It seems that the problem with my attic now is not enough intake ventilation from the soffit vents since the frost in the attic is most prominent at the ends of the roof. It looks like the plywood simply goes to the end of the soffit, therefore, there are no holes to vent from. I have gable ends, but these do not seem to be enough to vent any warm air that may be escaping from my home into the attic.


I may need to get a ridge vent installed on the peak of my roof for now because I can't do much about the soffit vents at the moment... in the spring I'm going to drill small holes in the plywood beneath the soffit vents (not too many to weaken the wood but enough to get some good aitflow going).


So it seems like I fixed one problem, but created another, or, the issue with the moisture was ventilation all along and not lack of insulation (though the extra insulation can't hurt I suppose).

The insulation is a big improvement, but probably what happened was that the initial moisture I had in there was being caused by warm air coming into the attic from the kitchen and bathroom upstairs, and because the soffit vents were not ventilating properly, this caused a temperature differential in the attic, which caused the condensation... so adding the insulation is keeping the warm air out more, but at the same time, the warm air that IS getting in is being trapped more, so when it hits the underside of the roof, which is much colder, it turns to frost..

frost is better than water, but still needs to be fixed.

Also, I have an air exchanger up there that currently does not work. I have bought a new one but it is too large to fit in the attic hatch

So ayways, I'm thinking the air exchanger vents may be contributing to the problem (small air leaks from these vents. I have some loose material that I could just stuff into the vents (similar to synthetic pillow stuffing), but not in the actual ducts. Also, should I seal off the intake/exhaust vents outside going to the air exchanger?

I'm looking for some opinions on this issue and what would be the best course of action to take at this point. I'm thinking the ridge vent is a good idea, but I have no idea how much something like this usually costs $$$.

Thanks in advance...

Eric.
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Old 01-05-2009, 12:07 PM   #2
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Recently Topped Up Attic with Blown Insulation...Now I have Frost/Condensation


Want to put an intake fan in a gable vent for the time being? Of course you will need adequate square inches of vent at the other end of the house to let warmer air out.

Also seal up any holes letting warm inside air up into the attic, including gaps in heating and air conditioning ducts as quickly as you can.

Nothing should exhaust directly into the attic. Outside exhaust ducts should not be near soffit vents or other attic vents where the exhaust air could find its way in.

If frost accumulates to look like balls, it will melt and drip all over the place even on a winter day when the sun is out and there is no snow on the roof.

Last edited by AllanJ; 01-05-2009 at 12:20 PM.
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Old 01-05-2009, 08:21 PM   #3
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Recently Topped Up Attic with Blown Insulation...Now I have Frost/Condensation


It seems like you have a decent understanding of the forces at work. The new insulation is helping keep the house warmer and the attic colder, but there's still moisture getting up there and not enough ventilation. It sounds like you have soffit vents and gable end vents. This condition typically doesn't work, especially on larger homes. You need soffit vents AND a ridge vent. When wind blows across your roof, a slight pressure differential causes air to be pulled out from the ridge vent which is replaced by air coming in from the soffit vents. Without both, the system doesn't work. Adding a ridge vent shouldn't cost much, I recently replaced a 40' long one for $500.
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Old 01-06-2009, 05:33 AM   #4
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Recently Topped Up Attic with Blown Insulation...Now I have Frost/Condensation


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Originally Posted by mpepin View Post
It seems like you have a decent understanding of the forces at work. The new insulation is helping keep the house warmer and the attic colder, but there's still moisture getting up there and not enough ventilation. It sounds like you have soffit vents and gable end vents. This condition typically doesn't work, especially on larger homes. You need soffit vents AND a ridge vent. When wind blows across your roof, a slight pressure differential causes air to be pulled out from the ridge vent which is replaced by air coming in from the soffit vents. Without both, the system doesn't work. Adding a ridge vent shouldn't cost much, I recently replaced a 40' long one for $500.
Yes, I do have soffit vents and gable ends. I don't think the soffit vents are doing much since when the contractor came over to add the insulation he noticed that they may be covered by the plywood from the roof and therefore not effeciently taking care of the ventilation. He suggested I remove the soffit vents, drill small holes into the plywood, then put the soffit vents back on.
My home is not very large. It is a 1300Sqft 4-level split. Problem is I have 2 roofs so I would need a ridge vent on both.

Do you think, the drill holes, on top of adding the ridge vent, is a good idea?

Thanks for the reply.
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Old 01-06-2009, 05:39 AM   #5
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Recently Topped Up Attic with Blown Insulation...Now I have Frost/Condensation


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Want to put an intake fan in a gable vent for the time being? Of course you will need adequate square inches of vent at the other end of the house to let warmer air out.

Also seal up any holes letting warm inside air up into the attic, including gaps in heating and air conditioning ducts as quickly as you can.

Nothing should exhaust directly into the attic. Outside exhaust ducts should not be near soffit vents or other attic vents where the exhaust air could find its way in.

If frost accumulates to look like balls, it will melt and drip all over the place even on a winter day when the sun is out and there is no snow on the roof.
Where can I get an intake fan? Like a local hardware store?
What can I use to seal these holes? I'm thinking, as I stated earlier, that a large amount of the moisture is most likely coming from a few places.

1. My 2 attic hatches are nothing more than slabs of fiberboard sitting on the hatch frame.

2.The bathroom fan (My wife, who just got home from the hospital with my new son was taking a bath when she heard dripping) I came directly home from work to realize that the dripping was caused by frost that had built-up on the metal casing of the fan and the steam from her bath caused it to melt. This is what lead me to investigate the attic when that's when I noticed the frost. The exhaust for this fan was initally blowing into my attic so we attached the hose to the gable end so that it vents directly outside now. My second bathroom on the third level's fan vents directly outside and does not go into the attic.

3. These Air Exchanger vents, which are not currently being used may be allowing warm air so seap through the openings in the ceiling. As I said, I do have some pillow stuffing type material that may help short-term...

What do you think about the idea of blocking the exchanger vents with this material?

Thanks for the reply.
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Old 01-06-2009, 07:56 AM   #6
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Recently Topped Up Attic with Blown Insulation...Now I have Frost/Condensation


I personally would not consider the powered vent an option at this point. Before you do that, you need to properly ventilate the roof. Drilling little holes near the soffit vents isn't adequate either, you need the full benefit of each vent you have. Even a powered fan needs excellent soffit ventilation in order to be effective.

As mentioned, cross-ventilation is critical. Soffit vents alone or ridge/rooftop/acorn vents alone are generally worthless...Both must be there and unobstructed to work effectively in conjunction with each other.

There are lots of ways to vent a roof. Here, you rarely see ridge vents. Instead, a number of square roof vents or spinning acorns are installed.
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Old 01-06-2009, 09:04 AM   #7
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Recently Topped Up Attic with Blown Insulation...Now I have Frost/Condensation


Hint: For an intake fan you might have an exhaust fan mounted backwards.

Unlike an exhaust fan, an intake fan does not have the tendency under some conditions to draw more warm humid air from the living space up into the attic.

The hose from the bathroom fan to the outside, should it run through the attic, should be insulated.

Anything, duct tape, etc. is better than nothing for sealing cracks where warm humid air from the living space or heating ducts gets into the attic.

For a whole house attic fan, at the very least cover the big louver in the ceiling with plastic sheeting taped all around but stuffing a blanket of insulation on top manually removed in the spring is even better. Same for the hatches.

Last edited by AllanJ; 01-06-2009 at 09:12 AM.
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Old 01-06-2009, 11:28 AM   #8
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Recently Topped Up Attic with Blown Insulation...Now I have Frost/Condensation


Ok, so I've installed some plastic over the attic hatches (The same you would use on windows in the winter) and I have stuffed the air exchanger vent with some pillow-type stuffing. So there potential air leaks are pretty sealed now. Hopefully this will at least slow the heat loss until I can get the attic ventilated properly.

The guy who topped off my attic should be here on Thursday to see what options we have, though I think a ridge vent/acorn is the way to go.

As I said, I have not been able to go outside and remove the soffit vent to see if in fact it is just one solid piece of plywood under those vents.

If so, what would be the best way to go about it?


Quote:
Originally Posted by AllanJ View Post

For a whole house attic fan, at the very least cover the big louver in the ceiling with plastic sheeting taped all around but stuffing a blanket of insulation on top manually removed in the spring is even better. Same for the hatches.
I'm not sure what you mean by "Louver" Sorry. :-(

Last edited by earthad1; 01-06-2009 at 11:56 AM.
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Old 01-06-2009, 12:04 PM   #9
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Recently Topped Up Attic with Blown Insulation...Now I have Frost/Condensation


Every electrical box you have in the ceiling lets house air into the attic. These can be sealed around the box with caulking. By code nothing should be in the box but wires and the connection points. The backside of the box where the wires come out can be sealed with fire-proof foam, but none can be in the box.

Think about how the house is built, I'm sure its all covered with insulation now, but typically electrical wires are run through the attic and then back down in each wall to an electrical box. Holes are drilled through sill plates and studs to get the wires to that point, they are often not resealed. That means you have air going up through your outlets into your wall and up into your attic. Solution is to seal up the electrical box at your wall best you can. I recently had thermal imaging done at my house that showed these problems.

Also, anywhere air comes in helps make the problem worse. If there are air leaks around windows that lets the air in more easily, these should all be sealed as well. I had major air leakage around my washing-machine supply and drainage panel that was covered up with a trim piece, and more around my dryer vent. Turns out air was leaking out of my house from just about every conceivable source.

Each doorway in the house leaks, the drywall isn't finished because it has trim covering it up. Sure enough the trim piece on the top of the door way isn't caulked (you can't see it anyway) and air leaks out (or in) there. That air must be going up into the attic. Some of the holes for the door knobs into the door frame were drilled too deep, sure enough air comes right through them.

It was quite an eye opener for me. There are lots of places to seal up.
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Old 01-06-2009, 12:16 PM   #10
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Recently Topped Up Attic with Blown Insulation...Now I have Frost/Condensation


yup..I wnet into my attic before the top up blown in was done..sealed all electrical fixtures with vapour barrier, caulk and spray foam....wire holes in top plates..pulled back insulation from eves..installed a few styro joist thingies..then blew it in..
I had solid sofits as well but drilled a few holes before doing the vented soffit covering..I have 6 roof vents and two big gable vents..but just in case
I am checking tomorrow for frost build up on nail heads.
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Old 01-06-2009, 12:32 PM   #11
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Recently Topped Up Attic with Blown Insulation...Now I have Frost/Condensation


Louver -- The semi-attractive grillwork that covers a fan opening or vent opening. For whole house attic fans it usually has movable parts to close off the opening but usually not good enough to prevent warm air from going up in winter.

Often the attic floor insulation, especially blown insulation, fills the eave soffit area and may even block existing soffit vents. Cutting new soffit vents therefore becomes a project. You need to clear away insulation and in most cases install (usually) styrofoam sheet baffles in the rafters to let air in and resist clogging as the insulation resettles.
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Old 01-06-2009, 12:50 PM   #12
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Recently Topped Up Attic with Blown Insulation...Now I have Frost/Condensation


you should also close up the gable vents after you
put in the ridge vent and cut adequate soffit ventilation
so you dont short circuit what your trying to achieve
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Old 01-06-2009, 06:08 PM   #13
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Recently Topped Up Attic with Blown Insulation...Now I have Frost/Condensation


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Originally Posted by strublesiding@optonline.n View Post
you should also close up the gable vents after you
put in the ridge vent and cut adequate soffit ventilation
so you dont short circuit what your trying to achieve
Yep! CMHC in Canada specifically forbids gable venting used in conjunction with soffit venting! In my home I placed a rubber seal all around the perimeter of the attic door jamb! I also glued a stack of stryrofoam on the top of the door also!
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Old 01-06-2009, 11:40 PM   #14
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Recently Topped Up Attic with Blown Insulation...Now I have Frost/Condensation


if you are getting that much condensation in your attic, did you make sure that you had a proper vapour barrier down before you had the insulation blown in? If not, the insulation maybe slowing the heat loss, but he moisture is still going through the same as before, if not faster since the inside of your house is warmer.

The plastic you put on your attic entries is pretty much useless, you need 6mm for a proper vapour barrier. I would also put a strip of rubber down where board lies. Since that piece isn't insulated, you might also think about buying some regular insulation so you can have a piece sitting on top of the board to insulate it.

As others have said, make sure your bathroom vent, as well as the vent over your stove both blow right outside, and not just into the attic.

An option for the stove fan is to replace it, and put in a new one that has a carbon filter and have it blow into the house so you don't have to do even more roof work, and it is one less area for warm air inside the house to leak out.
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Old 01-07-2009, 11:31 AM   #15
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Recently Topped Up Attic with Blown Insulation...Now I have Frost/Condensation


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Yep! CMHC in Canada specifically forbids gable venting used in conjunction with soffit venting! In my home I placed a rubber seal all around the perimeter of the attic door jamb! I also glued a stack of stryrofoam on the top of the door also!

Hmmm, interesting... Could this be why my soffit vents may be sealed off? Because I have 2 gable vents???
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