Blown in Fiberglass or Cellulose in walls with no vapor barrier

thwyld1October 12, 2011

Hi Everyone! I'm in need of some advice. I have finally decided to address the lack of insulation in the exterior walls of my early 1950s home. I have vinyl siding with a 1/4 inch layer of pink foam insulation under it and a layer of what appears to be heavy silver faced paper under that. I was planning to blow in cellulose insulation from Lowes using one of their machines. I did the attic several years ago and it was a breeze. I stopped by Lowes last night and the guy working there told me that without a vapor barrier, I should definitely go with the blown in Fiberglass product, not cellulose. He said that if the cellulose gets wet, mold can be a problem and this is not the case with Fiberglass. They will probably cost about the same, but fiberglass has slightly lower R value and is historically a pain (or should I say itch) to work with. Can anyone confirm or deny his claims of mold problems and/or provide any other relevant comments.

Thanks!

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thwyld1

Of course I did just find this post (by brickeyee, third post down) talking a bit about the absorbent properties of each and it makes cellulose sound better.....so confusing!

Here is a link that might be useful: Comparison Link - Click Here!

    Bookmark   October 12, 2011 at 1:22PM
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worthy

The building science knowledge of the guys at the Big Boxes frequently leaves a lot to be desired. Paul Fisette of the University of Massachusetts is a big fan of cellulose insulation. As is Dr. Lstiburek of Building Science Corp. See link below.

Here is a link that might be useful: Cellulose and Dense Pack Insulation

    Bookmark   October 12, 2011 at 11:56PM
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columbusguy1

The city blew cellulose into my outer walls in '88 after my first winter in the house...I have wood siding, no vapor barrier beyond some rosin paper, and I've had no problems so far twenty years on--except for a couple spots I think they missed--I need to get an ir inspection to see where it needs to be topped off.

The house was built in 1908, and the cellulose cut my heating costs more than in half! An older house is difficult to seal so tight that mold might be a major issue except around bath and kitchen leaks.

    Bookmark   October 13, 2011 at 2:40AM
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columbusguy1

Oh, I read somewhere that multiple layers of paint/paper can act as a sort of vapor barrier--but they do make some newer products you can use to accomplish the barrier.

Can anyone confirm that, worthy? Brick?

    Bookmark   October 13, 2011 at 2:46AM
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thwyld1

I read both links, which are very well done. Thanks. My only concern is the 1/4" of foam insulation under my vinyl siding. Would this act as a vapor barrier and hold any moisture in the cellulose?

    Bookmark   October 13, 2011 at 10:11AM
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brickeyee

Asking about insulation without also posting a location is not likely to get very good answers.

What works in the south (often a mostly cooling climate) often is not as effective in the far north (mostly heating and very cold temperatures).

The mixed heating-cooling zone needs another style.

    Bookmark   October 13, 2011 at 12:07PM
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thwyld1

Good point. I'm in central PA. Mostly heating, but the house does also have central air.

    Bookmark   October 13, 2011 at 2:01PM
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brickeyee

"Mostly heating, but the house does also have central air."

How many degree days of heating? degree days of cooling?

PA is all over the place.

Typical winter low?
Summer high & humidity?

All these things come into play.

In many parts of the the US a vapor barrier is not actually doing anything much.
It can only be on one side of the insulation, and with relatively equal heating and cooling loads should just be omitted.

Frost freezing in cold attics is a very cold weather occurrence.
It simply does not happen in the more temperate areas.

One of the problems we have is trying to establish energy codes that cover insulation and things like vapor barriers that are uniformly applicable across the whole nation.

With the wide range of weather it is simply destined to fail.

    Bookmark   October 13, 2011 at 4:41PM
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inox

Here is a detailed, illustrated discussion of vapor barriers, the various zones of the USA, and their requirements:

Here is a link that might be useful: BSD-106: Understanding Vapor Barriers

    Bookmark   October 13, 2011 at 6:01PM
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worthy

My only concern is the 1/4" of foam insulation under my vinyl siding.

A .25" of XPS (or EPS) is vapour semi-permeable, so you need have no fear of a double vapour barrier trapping moisture. In your primarily heating climate, a vapour retarder goes in the interior. A coat of latex paint does it.

    Bookmark   October 13, 2011 at 9:17PM
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thwyld1

Worthy, if what you say is true. I am golden and good to go. Thanks to all that offered advice. After Sunday, I'll be completely surrounded by cellulose....and hopefully a lower heating bill to go along with it!

Thanks again!

    Bookmark   October 14, 2011 at 8:39AM
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worthy

Worthy, if what you say is true.

According to BSC RR-0412, page 5.

"Materials that are generally classed as vapor semi-permeable to water vapor are:
* plywood,
* bitumen impregnated kraft paper,
* OSB,
* unfaced expanded polystyrene (EPS),
* unfaced extruded polystyrene( XPS) "1-inch thick or less,
* fiber-faced isocyanurate,
* heavy asphalt impregnated building papers (#30building paper), and
* most latex-based paints."

#emphasis added

    Bookmark   October 14, 2011 at 11:34AM
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