1. Having fiberglass insulation blown into an older home that has wood lathe plaster walls. Exterior is vinyl sided. Contractor will remove pieces of siding, drill holes and blow in the insulation. Does the plaster provide a vapor barrier or should the interior walls be painted with a ‘vapor barrier’ paint?
2. Same house has a finished attic. The ceiling is sheet rock attached to the roof rafters. Contractor wants to blow the fiber glass insulation into the space between the sheet rock and the roof decking. Is it ok to have the insulation against the roof decking or should there be an air space under the roof decking?
3. Is blown in fiberglass better than blown in cellulose?
Thank You
Replies
Personally, I'd do cellulose rather than fiberglass. Most would declare it more green and generally a better material to limit air movement through it ... and probably cheaper or no more expensive.
A vapor barrier paint on the inside would be good. It's readily available and inexpensive. Make sure you check your ventilation system (i.e. exhaust fans). Make sure they are doing a good job. Insulating older existing w/out proper venting can lead to problems (unless it tends to be leaky construction in general).
Re: ceiling and no venting ... other posters may have some good/better advice. You can do the non vented, but you need to ensure there isn't moist air getting into the attic (e.g. in the ceiling outside the knee walls or flat ceiling in the center of the attic). I think the unvented roof requires a well sealed ceiling. Don't forget e.g. piping and chases that run up into the attic from below. Those are also sources of moisture movement. Guaranteeing a sealed ceiling/attic in older construction MAY be more difficult than e.g. new. I think I have this concept right ... other posters can add, clarify, or correct me.
Is your climate hot, cold, or mixed?
Never mind, I just looked at your profile. I would call your climate mixed, and therefore be disinclined toe worry about a vapor barrier paint. Some ability for the wall cavity to dry to the inside of the structure is a good thing in a mixed climate. Though any paint you put more than one coat of on will act as something of a vapor barrier.
I prefer cellulose, though have no experience with blown FG.
How deep are the rafters in your cathedral ceiling situation?
Steve
Edited 9/11/2009 11:34 am by mmoogie
Not sure of the rafter size.. I'll check. Stay tuned.
Typically you would want to maintain an airspace between the insulation and the roof sheathing.
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