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Ceiling insulation question

Posted by orourke (My Page) on
Sat, Sep 26, 09 at 12:35

Question: On ceilings where the wallboard has an aluminum foil backing (which I assume serves as a vapor barrier?) there is no need to use Craft paper backed insulation. Plain fiberglass mats will do. Right?

I am redoing my attics insulation
There is already some fiberglass insulation in the attic but it is only R-11, has craft paper, and it is installed backwards (Craft paper side up!). It is 50 years old, the Craft paper is very brittle and has many holes anyway (perhaps a good thing in this case, since it is installed backwards).

In any case, my upgrade plan is to remove the craft paper from these existing R-11 old mats (if I can) and re-lay down just the fiberglass. Then Im planning to add another layer of, say, R-13 mats (plain mats - no Craft paper) to increase the R factor (to an R-24 total).

Does this sound like a logical plan?


Follow-Up Postings:

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RE: Ceiling insulation question

Have you considered diy blown in cellulose. In most areas you can rent the blower, in many cases free if you purchase the insulation from them. It's better at filling existing voids, around protrusions, etc. As with most any insulation type, you want to be careful to not block any venting as well as be careful around certain electrical lighting boxes as well as other mechanicals you might have up there, but a tighter insultion value is achieved with blown in.


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RE: Ceiling insulation question

The foil or craft paper does function as a vapor barrier keep warm moist air from the home from condensing in the insulation. It should be installed facing the interior of the home. You should install plain (unfaced) insulation over the old stuff.

As was suggested, blown-in insulation is a good way to go for the reasons described. It's relatively easy to do but does require two people, one to operate the business end of the hose and one to feed the machine. Cellulose and fiberglass are both available although cellulose is generally more readily available at home centers.

You may want to see what the recommended level of insulation is for your area of the country. Around here it is R38. The correct amount of insulation can be one of the most cost effective methods of controlling utility costs.

Here is a link that might be useful: Recommended Attic Insulation


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RE: Ceiling insulation question

Thanks for your replies,

I want to keep the existing insulation, not necessarily to save money but to avoid having to remove 1200sqf of insulation and then also having to dispose of it.

So can I blow some cellulose over the existing fiberglass (once I turn it Kraft paper down or even remove the paper altogether)?

My ceiling joists are only 2x6, so theres not much room for a lot of insulation. Im weary of burying the joists because, I imagine, it will become very difficult to move around in the attic when you dont know where the joists are. Hence, I thought, the R-20 limit on what I can put up there. I live in central California. I imagine insulation needs are not that demanding here. But I dont have much experience applying insulation, so I may be totally off track in my thinking here.

With the cellulose, Im afraid of blocking the vents (vents at eave are simply round holes on the frieze blocks). Seems like I would need to put some sort of shield where the eave vents are, otherwise, seems to me, it will be impossible to prevent cellulose from smothering them.


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RE: Ceiling insulation question

You can go higher above the joisting with cellulose, but you might want to frame up a cat walk on top of the joists for when you need to go up there. 2x6 catwalk with plywood would suffice I would think. If you decide on cellulose, plywood, masonite, or even a heavy cardboard can make vent sheilds keeping the cellulose from plugging the vents. My wife is from Stockton and I know the winters are fairly cold and damp, but not extreme, so maybe your idea of just adding batts would be sufficient. For any protrusions or areas of concern involving voids where you cant get peices of batting in, you could spray can foam in those areas before you layer the extra batting. I would remove the existing kraft facing as it could trap moisture between the new batts and old, but if your attic is properly vented, moisture shouldn't be a concern making the removal of the kraft unnecessary.


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RE: Ceiling insulation question

HD & Lowes sell attic vent protection EXTREMELY cheap.

These are flimsy foam 'egg shell carton' type stuff that is just stapled to your rafters. Creates a small covered airspace, and keeps the insulation from blocking vents. Each piece is about 4' long or so... fits between the roofing rafters.


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RE: Ceiling insulation question

I forgot to mention one of the downsides to cellulose.It compresses when you walk on it, set anything with a minute weight on it, losing r-value. That's more the reason for a cat walk. Some folks who dont use their attic that often keep a bag handy and loose fill where compressed when they have to go up there.


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