Recently Topped Up Attic with Blown Insulation...Now I have Frost/Condensation

earthad1

After reading a bit more on this, I'm confused. So am I supposed to have a vapor barrier on the attic floor or not?

http://www.cmhc-schl.gc.ca/en/co/mah...efcosa_002.cfm

"Attic Insulation The attic is often the most cost-effective place to add insulation. Usually, a contractor blows loose fill into and over the top of ceiling joists. For the do-it-yourselfer, batts laid sideways on existing insulation are an easy alternative.

• The air barrier at the ceiling line must be tight to ensure warm moist air from the house does not get into the cold attic and condense in the winter. Check ceiling light fixtures, the tops of interior walls and penetrations such as plumbing stacks for air leakage.
• Ensure that soffit venting is not blocked by added insulation; baffles may have to be installed."

My house was built in 1978-1980 so I'm guessing that if I lift up the insulation that's in the attic, I'm going to see a vapor barrier?

Gary in WA

Sorry I gave you the wrong idea in not being specific enough. I should have said- Check to see from the BSC site if plastic (Class 1) is required or just a Class 2, vapor barrier primer paint on the lid from below. In your case the plastic would be extremely hard to do..... after the fact. V.b. vs v.r.; http://www.energysavers.gov/your_hom.../mytopic=11810

Is the frost at the sheathing/gable framing because the fan moisture is trying the exit and because it is colder there, condensing and freezing?

Just cut a new bath fan hole lower down on the gable, just above the insulation. Run ducting up at the fan to get some fall over the rest of run for drainage. Be sure to insulate and v.b. the ducting, air seal all joints (even the individual elbow ones). Another option; http://homes.winnipegfreepress.com/i...article&id=702

Gary

__________________

mem

Staples to hold the baffles is fine. They are lightweight and should stay put that way.

I believe you would be in a zone 7 climate and would need a vapor barrier. The vapor barrier would prevent moisture from making its way up into the attic in the first place, as long as it is air sealed well--which it sounds like you've done.

As the names imply, a vapor retarder merely slows down the migration of water vapor where as a vapor barrier blocks it nearly completely. The kraft facing on fiberglass batts is a vapor retarder and 6 mil poly is a barrier.

If you dig down thru your insulation and find a layer of thick plastic (≥ 6 mil) you have a vapor barrier. It would need to be the layer just above the finished ceiling to work properly (the warm-in-winter side of the insulation). I'm also curious as to how you are aware that newer homes in the area don't use a vapor barrier.

earthad1

Thanks Gary, and yes, it could be that the fan is not venting as well as I had hoped, and the vapor is getting trapped under the peak, condensing, running down and freezing. We don't use the bathroom fan all that often as I take showers in the bathroom downstairs and not this one, but heat would constantly be escaping. I'm thinking cutting in lower is a good plan...

I was thinking, the fan is only about 2 feet from an exterior wall in the bathroom, I'll take a photo of the bathroom/wall and the one in the attic where the pipe comes in... I might be able to run it that way...much shorter distance.

There is frost on the other side of the attic also at the other gable, but its not as bad as the side with the fan venting out.

@mem: As far as the vapor barrier issue, I though I had seen some posts about that in this thread... I must be mistaken.

I'm thinking, looking back, the frost issue has been the poor installation of the ridge vent the entire time :-(
For starters, I'm going to go up there this weekend, check for vapor barrier, and I'm going to remove those pieces of batten insulation that are blocking the baffles out to the soffits. Hopefully that increases the airflow up to the ridge vent and reduces the frost.

What do you guys think?

So in the spring, I'm going to hire a roofer to properly cut the ridge to the recommended size and install this type of ridge vent:

http://www.airvent.com/homeowner/products/ridgeVents-shingleVent.shtml

http://homehardware.ca/en/rec/index....1?Ntt=2672-281

and have him install these




I'll then install those continuous soffit vents around the entire house.

wilsonstark

Just as a note, those things look pretty cool, but you can also make perfectly good channels of a similar type, precisely fitted to your attic using blocks of 2x2 (to space it off the roof sheathing) and either plywood or xps foam board. Might be more affordable and DIY. I know my roof has those and the sections I have had open to check have kept those channels clear for air to flow up quite nicely.

mem

I'm sure that would work just fine as well, but it's got to be a ton more work with cutting, fitting and nailing up there. And you'll have at least four pieces to fit per bay! bizrate has the AccuVent listed at Home Depot for $1.68 each for the model that fits 24" rafter spacing. I don't see how you'll beat that with wood and/or foam. You can carry up a whole house worth in one trip, trim them if necessary with just a pair of scissors and tack 'em up with a half dozen staples--definitely a DIY job, maybe five minutes per bay if you're taking your time.

wilsonstark

Wow. I can't argue, that's not big money price at all. Thought they'd be more