Vapor barrier exception?


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Old 05-10-20, 03:55 AM
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Vapor barrier exception?

Working on my son's 1924 house, which has an addition. We have removed the insulation in the attic of the addition due to moisture/mold issues from previous owner blocking soffit vents.

The ceiling is acoustical tiles (Pretty sure they are asbestos, the addition is probably from the '40s) which have been painted.

The substrate for the tiles is some sort of particle board.

I think it is pretty porous material. There is no sign of moisture damage in the ceiling material.

I know this should all be torn out but that is not in the cards for this year.

We are going to install fiberglass batts.

My question is should we use faced batts for the 1st layer since the ceiling is not sheetrock?

There is plenty of ventilation now. Climate zone 5.
 
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Old 05-10-20, 06:23 AM
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The terms are used interchangeably, what you want is a class 3 retarder.

You need something, paints and primers are generally enough to provide the rating, but your description of what you have on the ceiling doesn't sound sufficient,

So something is needed!

Another option is cellulose, the produce itself does not need a retarder due to density, it is heavy so helps with air flow, and it's much easier to install.

https://www.cellulose.org/Cellulose-...ame=HomeOwners
 
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Old 05-10-20, 06:44 AM
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If you use faced insulation you won't be able to staple it, since you don't plan to tear the ceiling down right now, but if you do decide to use it- your Kraft facing (a class II vapor retarder) should face the interior warm side. From what I have been reading, class II vapor retarder is suggested in ventilated attics in zones 6 and 7 (just to the north) while zone 5 can have either class II or class III. If your ceiling is not painted, then yes, you should use Kraft faced insulation. If you intend to drywall and paint ceilings later, you could probably get by with unfaced until then.

If you do tear the ceiling down someday, you could also staple the Kraft facing then. But until its stapled, it's not really completely effective as a retarder, since all the edges are laying open.

If you plan to tear the ceiling down someday you would not likely want to use cellulose or any other type of blow in insulation.

Cellulose is classified by the department of energy as a class III vapor retarder. So if your zone and code requires class II, cellulose alone does not meet that higher standard, should they choose to enforce it.

https://cellulose.org/GreenestInsula...-air-barriers/

Walls, ventilated cladding walls and ventilated ceilings are also different in how they are built and how they perform. So you have much discussion and confusion about what is required, what is best across all the different climates and zones in the US.
 

Last edited by XSleeper; 05-10-20 at 07:12 AM.
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Old 05-11-20, 06:58 PM
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Thank you for the replies. My son wants to use batts so he can work on the attic/ceiling in the future & not have to vac out celluose again.

BTW I forgot to mention, in OP, that the original insulation was rockwool with a tar paper retarder. It was tacked to the top of the 2X4 ceiling joists, so there was large gaps to the ceiling deck. Sometime in the last 60 years they blew a few more inches of cellulose on top of that.

What is really wierd is that the joists do not go sideways (they do not tie the bottom of rafters together). Amazingly, the ridgeboard is not drooping in the middle, as I've seen on poorly built garages. The addition is only about 12 x 12 so maybe that is why it is surviving.
 
 

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