Attic insulation above false ceilings?


Old 08-23-01, 07:22 AM
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One of the last things on the to-do list this year is to insulate the 1000 sq ft attic in our 150+ yr old house in upstate NY. When we moved into the house last year it came with enough R-25 fiberglass rolls to do the attic (so I'd like to use it, rather than blowing insulation I'd have to buy).

However... the upstairs originally had 10-foot ceilings with plaster and lathe. When the plaster started coming down, a previous owner dropped the ceiling by 2 feet and finished with sheetrock. So if Superman looked up from our bedroom with x-ray vision he'd see: a) sheetrock over 2x4, b) 2 feet of air space, c) plaster & lathe over 2x6, d) the attic, e) the roof.

Question - do I put the insulation on the floor of the attic (on top of the plaster and lathe), or do I try to get it onto the upstairs ceilings?

And taking into consideration the climate: 190+ inches of bitterly cold snow over a 6-month period last year, where should I put the vapor barrier (and should I be concerned about the space between the ceilings?)

There's not a shred of insulation anywhere right now, so it's a clean slate to start on.

Thanks in advance for any advice you can give,

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Old 08-30-01, 11:09 AM
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The answer is you put the insulation where you want to stop losing heat.

If you insulate the 2x6 plaster and lathe portion, heat will rise in the rooms until it reaches the insulation. That means you will be heating the 2' of dead air space.

If you insulate the 2x4 sheetrock ceiling, heat loss will stop at that point. 2x4 is typically too small to support a ceiling unless it is engineered truss systems. If you decide to insulate this space, take extreme caution putting your body weight or other weight on the false ceiling.

The vapor barrier is the first layer between the living space and the insulation. The next layer is the insulation. If you have faced insulation, the kraft facing is your vapor barrier and should be next to the living space. In either case false ceiling or origonal ceiling, the kraft paper should be down towards the living space with fiberglass up towards the roof.

R-25 is far better than no insulation. Most recommendations indicate at least R-38 for ceilings. If you decide to put addtional insulation on top of the roll/batt insulation, use unfaced or blown. A second vapor barrier will trap moisture between the two barriers and rot your framing members while growing mold and mildew.

A point to consider is if you ever plan on removing the false ceiling. If there are plans to remove the false ceiling, then insulate the plaster & lathe.
Old 08-30-01, 02:42 PM
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I just love old houses, especially when the other guy leaves you all the problems.

See my ansewer to "keeneye" in the basement heading.
Use the wall method only sub 1"x2" strips and install a second layer. To any exterior wall exposure install one layer( or two). Requires a air nailer and stapler. Low weight means easier faster insulation. DON'T FORGET TO BRACE THE FALSE CEILING.

If you have a frame or masonry house and want to super insulate the walls use this same method.

If you have other rooms to do you can use this method.
Fast, very efficient, super vapor barrier, no mold and does not lose insulation values.

Thank you for considering my personal opinion.
If you have any further questions, please let know.
Old 08-31-01, 02:10 PM
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Thanks for the answers. I hadn't thought about taking the ceilings out. I have no plans to do so right now, but when we insulate the walls we might have to... I guess I'll put 2 layers of R25 at the 2x6 attic level. Is there such a thing as too much inulation? We have enough R25 to go over the attic twice (faced with unfaced on top) and no place else in the house it will fit in.

And one more (dumb?) question - when putting down faced insulation should it be stapled, or is gravity enough to do the job. It seems like a lot of work digging through the insulation to staple it, but if it's how it should be done then that's the way I'll do it!

Thanks again,

Old 09-01-01, 05:39 PM
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Anything over "R" 19 you're wasting money. Not only will you never save enough enery to pay for it, The extra mass could cause you to have higher cooling bills. Glass absorbs over 90% of the heat energy.

The Radiant barriers will perform better than the fiberglass.
Old 09-04-01, 02:23 AM
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No need to staple. Gravity will work for attic insulation.

"Anything over "R" 19 you're wasting money. Not only will you never save enough enery to pay for it"

That may be true if you were paying for the materials. You mentioned you already had the materials for free. Every inch of insulation over 6 is less effective than the previous in terms of payback but in this case there is zero cost for materials.

I would recommend you run the first layer of faced insulation in between the ceiling joists. Run the second layer of insulation perpendicular to the joists. This will add a layer of insulation overtop the joists. Wood is considered a poor insulator and by running the insulation perpendicular, you will cover the wood joists.

Before you insulate, get a few cans of foam-in-a-can. Look for places where utilites puncture the framing and fill the hole around the utility. This will help reduce air infiltration. Older homes are notoriously drafty. This will be the first step in reducing air infilteration.

Also think about installing some insulation under the floor. This will help reduce heat sink. Again fill the holes in the framing with foam-in-a-can prior to insulation. If you don't have the time or money to insulate right away, at least you can start the job with the foam-in-a-can. $3 a can. You might use 4 cans for the entire house. Quick and cheap.

rbisys appears to be a professional radiant barrier installer. That should make him knowledgeable about radiant barrier systems and how effective they are. He can probably advise you well on those systems.
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