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Old 07-14-2012, 12:14 PM   #1
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Attic insulation and vapour barrier


I did some reading through on other post and have a general idea of how this should be done but I'm still a bit confuse.

The ceiling at the cottage is down to run some new electrical. There was no insulation. I want to put insulation in.

Q: Do I put vapour barrier on the bottom of the rafter, then add some pink fiberglass on top of the vapour barrie Or does the vapour barrier need to be put up at all?

I understand wall insulation and the vapour barrier is attached on the outside of you studs(interior side) but I just dont know if you do the same thing for an attic??

Here are a couple pics of the space. I live in Ontario, Canada.

Thanks for the help!
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Attic insulation and vapour barrier-image-119906358.jpg   Attic insulation and vapour barrier-image-119081691.jpg  

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Old 07-14-2012, 12:21 PM   #2
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Attic insulation and vapour barrier


Is the space conditioned?

Is the attic/roof vented?

Theoretically, the vapor retarder would go across the bottom chords of the trusses prior to re-drywalling.

I would rather see an airtight ceiling than a ceiling with a vapor barrier in it if I had to choose between the two.

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Old 07-14-2012, 12:45 PM   #3
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Attic insulation and vapour barrier


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Originally Posted by Windows on Wash
Is the space conditioned?

Is the attic/roof vented?

Theoretically, the vapor retarder would go across the bottom chords of the trusses prior to re-drywalling.

I would rather see an airtight ceiling than a ceiling with a vapor barrier in it if I had to choose between the two.
There are no vents right now in this attic and i believe there are no cut outs in the soffit as well.

The plan is to put up a barn board ceiling for a rustic look inside.
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Old 07-14-2012, 12:48 PM   #4
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Attic insulation and vapour barrier


Vapour barrier goes on the interior side, and it is required by the building code. You should also have ventilation in the attic space.
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Old 07-16-2012, 06:43 AM   #5
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Attic insulation and vapour barrier


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Originally Posted by shazapple View Post
and it is required by the building code.
That's not exactly true...

The National Building Code of Canada specifies that vapour barriers are not required when
it can be shown that uncontrolled vapour diffusion will not adversely affect any of, (a)
health or safety of building users, (b) the intended use of the building, or (c) the operation of
the building services.
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Old 07-17-2012, 10:02 PM   #6
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Attic insulation and vapour barrier


Based on what I've read I think I'll need vapour barrier....

The barn board wouldn't be air tight so the vapour barrier would be needed based on that reason.

So if I used vapour barrier with a blown in or bat insulation, would that work fine(along with me getting ventilation up there)

Here's my other thought.... What about closed cell foam insulation in this situation? It's vapour barrier and insulation in one. Your thoughts??
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Old 07-17-2012, 11:49 PM   #7
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Attic insulation and vapour barrier


what is wrong w/ putting plywood on the bottom of the truss chords, taping and gooing the edges, then blowing in cellulose over that? with the distance between trusses that you have, adding in 2x4's between then to nail the plywood to may be advisable. the ply is your air barrier. if you have the head room, you can then screw 2x4's to the truss chords for a 3.5" chase for "stuff" and not ding your air barrier. attach the rustic boards to the 2x4's. just a thought.
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Old 07-18-2012, 11:23 PM   #8
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Attic insulation and vapour barrier


I think it would be cheaper to just use vapour barrier instead of putting up plywood.

I'm just wondering about a spray foam instead of bat or blown??? But I'm sure spray is pretty expensive and I don't know if there is enough benefits from using it to go ahead with it.
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Old 07-19-2012, 12:16 AM   #9
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Attic insulation and vapour barrier


sure a vb is cheaper.... in the short run. if you have trouble because of it, that will be expensive. cellulose is also much better insulation than batts.
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Old 07-20-2012, 07:46 AM   #10
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Attic insulation and vapour barrier


The way things work....Water vapour is created in the home by cooking, washing, breathing, sweating.
Water vapour is programmed to move towards a cold area/surface.
Water vapour passes through the ceiling, through the insulation and turns into condensation (if the roof is warm enough) then ice (if its cold)
The only place to put a vapour barrier is below the ceiling joists and above the drywall.
The vapour barrier needs to be kept as warm as the room below, otherwise condensation will form on the vapour barrier and make the drywall wet.

Most home have drywall topped by fibreglass both of these are transparent to water vapour..... it merely rises through them, lands on the nearest cold surface and turns to condensation or ice.

Your often see condensation frozen in the roof on nail heads, shining bright as frost
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Old 07-20-2012, 11:14 AM   #11
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Attic insulation and vapour barrier


"...and turns into condensation (if the roof is warm enough)..." vapor condenses on colder surfaces.
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Old 07-21-2012, 12:16 AM   #12
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Attic insulation and vapour barrier


What is your ceiling joist/rafter ties span, I doubt cellulose will stay up as they already appear sagging.....

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Old 07-21-2012, 06:09 AM   #13
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Attic insulation and vapour barrier


Quote:
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"...and turns into condensation (if the roof is warm enough)..." vapor condenses on colder surfaces.
We are writing about winter time...cold outside warm comfort zone, cold roof.
Warm means about 7C down to 0C.
Mold forms from about 22 down to 7C, condensation shows from about 7 down to 0C....then frost and ice!
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Old 07-22-2012, 03:52 PM   #14
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Attic insulation and vapour barrier


"if the roof is warm enough". i thought you mis-typed and meant to say "if... cold enough" to form condensation. later. j
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Old 07-25-2012, 08:49 AM   #15
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Attic insulation and vapour barrier


I'll have to measure the span but I'm not back to the cottage till the 2nd of Aug....

This cottage will have very cold and very hot conditions. Lows down to -30C and highs to 30C.

I appreciate all the feedback folks! Keep it coming

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