Insulation, Radiant and Vapor Barriers - Confused about Insulation (Question Moved)

We just got our electrical and plumbing rough in inspected last week, so we are ready to move on to insulation. After reading through the basement forum and the article on www.buildingscience.com, I'm a little confused.

Our framed walls use wood studs (sole plate is treated) and are approximately a 0.5 - 1 inch away from the foundation. After talking to the city inspector, the code requires the use of a vapor barrier on the inside wall between the insulation and drywall. So, I was going to use unfaced batts of fiberglass, 6 mil poly vapor barrier, and drywall. However, when I looked at the article at <http://www.buildingscience.com/resources/foundations/Basement_Insulation_Systems-2002.pdf>, the article talks about this very same setup and calls it unacceptable (Photograph 2) due to possible mold, etc. They recommend a rigid foam against the foundation wall. Since my framing walls are up (and electrical between the studs), this is impossible.

What are your thoughts? I hate to use my original setup when I know that there is a good possibility for mold. On a side note, our house is about 4.5 yrs old and we haven't had any moisture issues.

Thanks,
B.

Why not use kraft faced insulation. The paper is a vapor barrier. Run this past your inspector first, though. You don't want to have a picky inspector tell you that it is not acceptable AFTER you install it.

The theoretical experts from around the world have many different (and opposing) opinions on moisture control, insulation and vapor transmissions. These are based on idealized situtations based on a 100% finished basement, which rarely is built. Usually you have some unfinished areas that are not isolated by perfectly sealed and insulated doors. This destroys all of the micro-thinking "new" suggestions.

Fortunately, these groups have no recognized authority and you have the obligation to build within your local requirements and make the variations you choose.

The first thing is comply with your local regulations since not everyone is from New England and builds the same way and has the same climatic conditions.

Dick

There are a lot of opinions on this. I personally like the "basement insulation systems" as it looks at the worst case situation, which I think is a valid point of view. And the fact that actual testing (experimental) and theoretical is used to arrive at conclusions makes it hard to disregard the paper.

If you have water vapor coming through the basement wall and a vapor barrier there is not where for the vapor to go. The dark wet environment seems like a good place for mold.

In addition is you don't any water vapor but there are leaks from the conditioned space to behind your insulation, the warm air coming in contact with the cooler walls will produce condensation. Remember that warm air can hold more moisture than cool air.

I would see if your local building inspector would allow you to put up kraft paper faced insulation and then slash up the paper a bit with a utility knife. Also make sure you only paint the walls with latex paint so they can breath. If it were me and the building inspector said no I'd slash up the insulation after he left and then put up the drywall.

- Mark

Mark has suggested a great way to deal with inward moisture drive.

However, the vapor barrier is there for a reason: to prevent interior humidity from condensing on the concrete during winter conditions. Whether or not it actually succeeds at this function is up for argument.

Point is, you still need to prevent humidity from getting to the wall, especially at the above grade areas. So slashing out the paper facing would necessitate air-sealing the drywall.


ALTERNATIVELY
There are cavity fill insulations out there that do not require vapor retarders. Talk to the manufacturers of these insulation systems to find out if their products are suitable for your application.


doug

I work for an insulation contractor and have been installing insulation for 3 years now and the best way to insulate a home if you want to spend the money is CORBOND. It's a spray foam, that is applied to the stud cavities to achieve a high R-value. The foam, when fully cured has it's own vapor barrier and this product is mold resistant. another idea is BIBS (blown in blanket system) they tack up a piece of cloth-like "netting" then blow the insulation into the cavities. Very clean and little to no dust. just some other ideas

Would you spray Corbond on the top half of the wall? Or the whole thing?

I'm pretty sure the BSC article mentions that there are issues that arise from installing vapor barrier foam on the bottom half of the wall. What happens to all the moisture that is trying to come inward from the soil?

I work for an insulation contractor and have been installing insulation for 3 years now and the best way to insulate a home if you want to spend the money is CORBOND. It's a spray foam, that is applied to the stud cavities to achieve a high R-value. The foam, when fully cured has it's own vapor barrier and this product is mold resistant. another idea is BIBS (blown in blanket system) they tack up a piece of cloth-like "netting" then blow the insulation into the cavities. Very clean and little to no dust. just some other ideas


Seems like a permanent way of insulating, which does not allow you to make any alterations to wiring etc after it is installed.

Em it's nearly R-7/inch.

You wouldn't put that large a thickness in to interrupt rewiring.

Doug,
It fills the cavity...haven't you ever seen this stuff applied???

You spray it in and it expands, then you scrape off any excess that expanded beyond the studs. It virtually seals your cavity.

Em

Corbond should not be confused with low-density spray applied polyurethane. Low-density polyurethane has a very high expansion rate, and often expands beyond the cavity. It has an R-Value of 3.6/inch, a very high perm rating, and is soft enough that wiring adjustments can be made after installation.

Corbond is a high-density spray applied polyurethane. It has a low expansion rate, and can be easily applied in thicknesses as low as 1/2-inch. It has an R-Value of 7/inch, and a very low perm rating. It is also very rigid, meaning that wiring adjustments cannot be made after installation, and you really can't screte it if you overfill the cavity either.

Milkbean, you aren't stuck yet.

You can slip 8'x2' pieces of 3/4" or 1" XPS in behind your studs horizontally. Pay close attention to the seems so that you have continious coverage. Then I would stick rock wool batts (like Roxul) in between your 2x4s instead of fibreglass since it is better able to handle any moisture without the risk of being a place for mold to develop. It also insulates better than f-g when wet or cold and is far less of a pain to work with.

With the XPS against the outer wall, and the rock wall in the cavities, you are covered. No vapour barrier is needed on the inside, just drywall and you're set.