Thread: Insulation question

Is it acceptable for fiberglass batt to be installed against the roof? The vapor barrier was facing the attic space. I know this is allowing conditioned air to escape into the attic. Dont see why anyone would install insulation against the roof sheathing even in a vaulted ceiling an airway is still needed.

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Originally Posted by cglochau

Is it acceptable for fiberglass batt to be installed against the roof?

Yes.

The vapor barrier was facing the attic space.

But not with the facing exposed as the facing is required to be in contact with drywall or other approved building material.

Dont see why anyone would install insulation against the roof sheathing even in a vaulted ceiling an airway is still needed.

It's done all the time, it is referred to a a non-vented sealed attic and the attic is 'conditioned space'.

Thanks Jerry I did some more reading and it makes sense now.

No! Probably not. Review ICC Section R806.4.
The insulation must be at least air impermeable by ASTM 283 (spray foam).
This is for good reason.
Joseph Lstibuek who authored the code, and his associates have written much about this subject and moisture control Building Science Corporation. I personally have seen numerous failures with what you describe.

Originally Posted by James Morshead

No! Probably not. Review ICC Section R806.4.
The insulation must be at least air impermeable by ASTM 283 (spray foam).
. . . . I personally have seen numerous failures with what you describe.

What would you describe as a failure for this type of installation?

Someone was probably trying to reduce the solar heat gain by putting the insulation at the roof. This is not going to do much and would be better off putting the insulation at the ceiling and making sure there is proper roof ventilation. If way it's installed can trap moisture against the bottom of the roof sheathing. Plus t
he exposed vapor barrier, if paper, is a fire hazard and is not to be left exposed. Most of the time it's printed right on it.

Originally Posted by James Morshead

No! Probably not. Review ICC Section R806.4.
The insulation must be at least air impermeable by ASTM 283 (spray foam).
This is for good reason.

Yes, review that section, it does not state what you are saying it does (read all of the options).

I'm guessing that the batt(s) in question have a kraft paper facing as the vapor barrier. Burns like Gasoline...(only hotter). An FSK-25 (foil) fire rated facing would be acceptable however, Most of the time you will see this in commercial buildings that have a suspended ceiling.

In my area the municipal building inspections must have been very lax before 1980, because I have run across two local elementary schools, (one was built in the 70s) that had Kraft faced batts installed in this manner.

Makes finding leaks a bitch, and then, you're not only fixing the leak, but probably dealing with molds and replacing the insulation too. Seen it done, wouldn't do it. JMO.

Originally Posted by Jim Hintz

Makes finding leaks a bitch, and then, you're not only fixing the leak, but probably dealing with molds and replacing the insulation too. Seen it done, wouldn't do it. JMO.

You bring up a good point about leaks and mold. I have always felt that installing any more than just a radiant barrier under the roof deck is asking for problems. And also the radiant barrier, if installed under the roof deck, should be "perforated". If a leak develops, you should be able to see where it is and it will not allow the moisture to build-up in the roof decking and framing members.

I also have some very strong (Negative) opinions about the "highly touted" (airtight) foam insulating systems that keep the attic inside the insulated building envelope. But that is for a different thread and for another day.

My concern would be: it seems that this could contribute to ice damming. If the attic space is heated space in the winter, snow on roof may melt and run down to the eaves, where it would freeze because it overhangs heated house, so not as heated. Turn to ice. What do you guys think?

Leon

The OP is in Florida, so ice damming is not an issue.

Originally Posted by Darrel Hood

The OP is in Florida, so ice damming is not an issue.

Yep' the only Ice Damming there is in Florida is when it freezes their orange Crop.

Oh' and the Illegals in Florida dam ICE also.

Thanks. I've never stayed in Florida long enough to know that it never snows. So...that's why everyone wants to go there in the winter!

Originally Posted by Larry Morrison

You bring up a good point about leaks and mold. I have always felt that installing any more than just a radiant barrier under the roof deck is asking for problems. And also the radiant barrier, if installed under the roof deck, should be "perforated". If a leak develops, you should be able to see where it is and it will not allow the moisture to build-up in the roof decking and framing members.

I also have some very strong (Negative) opinions about the "highly touted" (airtight) foam insulating systems that keep the attic inside the insulated building envelope. But that is for a different thread and for another day.

The sheathing also turns dark / black due to the inability for air to circulate and heat to dissipate - seen it many times.