Kraft Paper

	Kraft Paper

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Subject

Author

Date

Kraft Paper

Don

01-15-2007

RicodJour

3D Peruna

Don

Bob Morrison

RicodJour

Michael Bulatov...

Bob Morrison

Don

Don

Michael Bulatov...

Pierre Levesque

Don

Bob Morrison

Pierre Levesque

Don

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Posted by Michael Bulatovich on January 16, 2007, 10:02 am

> RicodJour wrote:

>> The kraft paper is part of the vapor barrier. There's some schmutz

>> sprayed onto the back of the paper that reduces the permeability and

>> bonds the fiberglass to the paper.

> Yeah...and you've seen a typical installation. Look at the seams...not a

> very effective vapor barrier. Maybe, just maybe, in a good drywall

> assembly with careful attention paid to the holes (electrical boxes,

> chases, etc)....

I've never used that stuff. The temp difference/vapor pressure is too great
and the consequences too significant.
--

MichaelB
www.michaelbulatovich.ca

Posted by Pierre Levesque on January 16, 2007, 4:43 pm

> What is the purpose of Kraft Paper on batt insulation?

> The reason I'm asking is that today I finished the insulation in my office

> and there were a few odd shaped cavities that I stuffed scraps of

> insulation into.

> That insulation did not have the brown kraft paper on it.

> I don't want condensation or thermal breaks or any other surprises after

> the drywall is up, so should I do anything to that exposed insulation?

> BTW: I'm using Johns Manville batts, R13 3.5" - walls, and R30 10.5" -

> ceiling.

I've never considered batt insulation with Kraft paper a vapor barrier
insulation. As far as I'm concerned the sole purpose of kraft papered batts
is for ease of fastening to vertical installations. In fact, kraft paper is
quite breathable. That said, it doesn't have zero vapor barrier quality but
it isn't the same as the same batts lined with plastic. Actually even JM's
website calls kraft faced batts "vapor retarder" not vapor barrier
http://tinyurl.com/2dwce7. For a proper vapor barrier I would line the
entire wall surface with a 6 mil polyethylene wrap layered horizontally top
to bottom and againt the vertical seams between the batts

Posted by Don on January 16, 2007, 7:44 pm

>> What is the purpose of Kraft Paper on batt insulation?

>> The reason I'm asking is that today I finished the insulation in my

>> office and there were a few odd shaped cavities that I stuffed scraps of

>> insulation into.

>> That insulation did not have the brown kraft paper on it.

>> I don't want condensation or thermal breaks or any other surprises after

>> the drywall is up, so should I do anything to that exposed insulation?

>> BTW: I'm using Johns Manville batts, R13 3.5" - walls, and R30 10.5" -

>> ceiling.

> I've never considered batt insulation with Kraft paper a vapor barrier

> insulation. As far as I'm concerned the sole purpose of kraft papered

> batts is for ease of fastening to vertical installations. In fact, kraft

> paper is quite breathable. That said, it doesn't have zero vapor barrier

> quality but it isn't the same as the same batts lined with plastic.

> Actually even JM's website calls kraft faced batts "vapor retarder" not

> vapor barrier http://tinyurl.com/2dwce7. For a proper vapor barrier I

> would line the entire wall surface with a 6 mil polyethylene wrap layered

> horizontally top to bottom and againt the vertical seams between the batts

Even though the outside of the building is wrapped with Tyvek?

Posted by Bob Morrison on January 16, 2007, 7:59 pm

In a previous post Don wrote...

> Even though the outside of the building is wrapped with Tyvek?

Yes. The vapor interior barrier is intended to keep room moisture from
infiltrating the insulation and reducing its effectiveness. The exterior
barrier (Tyvek) is intended to keep leaks outside the structural envelope
and to allow any moisture vapor that might make make it into the
insulation to migrate out of the building envelope.

Nothing like taking Alaska's Cold Regions Engineering Short Course to
learn a ton of stuff about cold weather construction! BTW, it is a
requirement for obtaining a license to practice in Alaska. Fortunately,
the course is taught in Seattle.

--
Bob Morrison, PE, SE
R L Morrison Engineering Co
Structural & Civil Engineering
Poulsbo WA
bob at rlmorrisonengr dot com

Posted by Pierre Levesque on January 16, 2007, 10:28 pm

> In a previous post Don wrote...

>> Even though the outside of the building is wrapped with Tyvek?

> Yes. The vapor interior barrier is intended to keep room moisture from

> infiltrating the insulation and reducing its effectiveness. The exterior

> barrier (Tyvek) is intended to keep leaks outside the structural envelope

> and to allow any moisture vapor that might make make it into the

> insulation to migrate out of the building envelope.

> Nothing like taking Alaska's Cold Regions Engineering Short Course to

> learn a ton of stuff about cold weather construction! BTW, it is a

> requirement for obtaining a license to practice in Alaska. Fortunately,

> the course is taught in Seattle.

> --

> Bob Morrison, PE, SE

> R L Morrison Engineering Co

> Structural & Civil Engineering

> Poulsbo WA

> bob at rlmorrisonengr dot com

Took the 'almost' exact words right out of my mouth Bob... thx...

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