Must do's when adding attic insulation

Combining batts, loose-fill fiberglass can create moisture issues

By Inman News Feed
Add Comment Add Comment | Comments: 0 | Posted Dec. 2, 2011

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Combining batts, loose-fill fiberglass can create moisture issues

Paul Bianchina
Inman News™

Q: I've had loose-fill fiberglass (insulation) in my attic since 1975. I have some new insulation with brown paper covering on one side so I need to know if that is called batts? If it is called insulation batts, then can I put them on top of loose-fill fiberglass? Which side would I put the batts: at bottom or at top?

In your article you wrote about "using unfaced batts only so that you don't create a double vapor barrier and trap moisture between the layers of batts." What does that mean? I want to understand about it clearly before I put them in the attic. --Becky F.

A: The type of insulation you describe, with the paper facing over the insulation, is indeed what is known as batts. The paper facing is the vapor barrier.

Here's a quick explanation of how it all works: Inside the house, you create moisture from cooking, bathing, etc. That moisture vapor in the air wants to move from a warm area to a cold area, so it's naturally always moving toward the ceiling and exterior walls of the house.

Vapor barriers are used to prevent that moisture from getting into enclosed areas where you don't want it, because once it gets in there, if it can't escape it can do a lot of damage.

For that reason, batt insulation often comes with a vapor barrier on one side. The vapor barrier is always installed facing the heated side of the wall or ceiling, because that's where the moisture is coming from.

Now let's look at your situation, which is a little different. You have loose-fill insulation in the attic, which doesn't have a vapor barrier. The theory is that part of the moisture vapor in the house is actually blocked by the drywall and paint on the ceiling.

Any moisture that does enter the attic will pass through the loose-fill insulation and exit the attic through the roof vents, so it won't cause any damage.

It's fine for you to install your batt insulation over the existing loose fill. However, you want to remove the paper vapor barrier first -- simply peel it off and discard it -- then lay the batts on top of the loose fill as gently as possible, so that you don't compress the old insulation.

If you don't remove the vapor barrier, you run the risk of trapping moisture vapor that passes through the loose fill against the vapor barrier, where it can't escape from the attic.

Q: We have the "new insulated window," and after 10 years we have had major condensation problems. Any thoughts? --Wilson R.

A: If the condensation is appearing between the panes of glass, then you have a broken seal in the insulated glass unit. Insulated glass works by trapping a layer of dead air between two panes of glass. If the seal is broken, moisture can get between the panes and condense, and it's very difficult to get rid of.

The only solution is to replace the insulated glass unit. You need to call a local glass company, and the company can make a site visit and measure your window. They'll order a new sealed glass unit -- just the glass, not the entire window -- that will be made to fit your particular window. Once the new glass unit arrives, on-site installation is fairly simple for most types of windows.

Q: Are brick-construction homes colder than a wooden home in the New England winter? --Glenn D.

A: If you're talking about a true brick construction, as opposed to a brick veneer over a standard insulated, wood-framed wall, then the answer is yes. You have several problems with full-brick construction when it comes to keeping them warm:

1. Brick has an R-value of approximately 0.2 per inch (which would equal 0.8 for a standard 4-inch brick). So if you have a typical double-brick wall that's 8 inches thick, you have an R-value that's less than R-2. On the other hand, a 6-inch wood-frame wall has an R-value that's more than 10 times that much.

2. Brick homes tend to have more air infiltration problems, due to the number of joints between the bricks. Even tiny gaps can add up to a lot of infiltration heat loss when multiplied over the size of the entire home.

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