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Old 03-17-2013, 01:18 AM   #1
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Attic insulation ideas/help


Just bought a 1985 home with vaulted ceilings and about an R-3 of insulation in the attic-if you dont count the massive air leaks around the return air vents and anything else that goes into the attic space.
The attic floor is 2"X6", and not well insulated with blow in fiberglass- at least where there is insulation.

SO, this is the plan thus far:

Take 1" R-max foil face rigid foam insulation and adhere it to the bottom of the roof sheathing and seal with expanding foam.
Use the fiberglass batts (that are going to come out of the vaulted ceilings) and batt under the R-max rigid foam insulation, I think this will work well, but....

Could I instead place thick plastic sheeting on the roof joists (inner attic side) as a vapor barrier and than blow in cellulose up to the roof sheathing and also use insulation batts? Would the plastic sheeting keep out moisture and keep the cellulose/ used batts dry?
I believe the cellulose and fiberglass batts will keep the cold outside air insulated from the warm/moist attic air, and the plastic sheeting will keep the inner moisture aware from the cellulose and used fiberglass batts

Also, I will be pulling the fiberglass batts out of the vaulted ceiling and "tight pack" cellulose to improve R value and use the tight pack method as a vapor barrier/retardant.

As far as walls-I've gutted my master bath down to the studs-r-11 fiberglass batts-except along the top plate, where there is no insulation for the entire span of the wall from the wall plate to the floor sheathing above.
The plan is to install 2" R-max rigid foam in between the studs (I know, there's going to be thermal bridging) and spray foam around the edges of the rigid insulation for a vapor barrier and than plastic sheeting vapor barrier under the dry wall.
This will create a1.5" air space between the rigid foam and the plastic sheeting/drywall combo.

Any suggestions on my plastic sheeting with cellulose between rafter joists-seems like it would insulate well and have a nice vapor barrier while keeping costs minimal.
Also, will there be a moisture issue between plastic sheeting installed underneath drywall in a bathroom and rigid foam in the wall cavity?

Thanks all.

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Old 03-17-2013, 02:48 AM   #2
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Attic insulation ideas/help


Just a FYI how is your roof going to breath? and because you live in the pacific north west we have a high moisture problem with the air here. You need HD Fiber glass batts in the vaulted part. and R 48 in the rest 17 inches there about for insulation. I have had sevral contractors both from a cellulose company and fiberglass company both told me that cellulose is not really advised in the pacific north west in attics it does poorly do to mosit air ventelation. The honest contractor with the paper mulch told me that it soaks up the humidity and molds the other stuff around it. Just what I have been told and i would just add more isulation because the roof needs to breath and seal up the holes

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Old 03-17-2013, 12:47 PM   #3
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Attic insulation ideas/help


Slow down a bit.

You are proposing some things, that if used in the wrong areas and applications, will completely exacerbate your issues and rot your roof out in a heartbeat.

Start off with some information about the home (location, style, venting, etc) and some pictures of the attic and the exterior.

As RTC mentioned, if you change the venting of the roof, you can royally mess things up if you aren't careful.
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Old 03-17-2013, 03:55 PM   #4
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To RTC_wa and windows on wash
Thanks for the replys

Location of home- Portland Oregon
Style of home, Mediterranean with 27 yr old tile roof-appears to be in good condition with no visualized leaks or issues, under sheathing is plywood with 2x12 rafter joists.

I'll submit pics when I can

The attic area is vaulted and has multiple peeks and vaulted ceiling runs around a central walk area.

The (horrible, but so far effective) venting is the occasional 2" hole in a row of three between rafters-with a plywood soffit that also has the occasional three row of 2" holes- the vent opening do not align and there is very little gap between rafters.
Surprisingly, the attic has no moisture problems other than a VERY light coat of black growth (near the bath vent at roof sheathing) that easily comes off with the brush of a hand- Despite an upstairs bathroom (6" vent) that was venting into the fiberglass blow in insulation for an unknown period. The previous occupants must have used only the Master bath because the attic structure/sheathing looks great.

I've since vented the bath fan out the soffit I am in the process of putting proper vented soffit's under the gutters-the previous occupants sealed the gutters to the soffit's with caulking........ the gutters do run under the roof tar paper though-so not as horrible as i had feared.

There is a bit of moisture in there-but nothing a little dry time and primer/sealer won't manage, the rafter ends are solid and no softening has been noted -my fault-I just discovered the bath vent into the insulation technique and just recently corrected it and am in the process of pulling out old soffit's.

As far as the attic breathing, I noted homes in Portland with sealed attics-usually spray foam, I realize that appropriate moisture venting will be needed and maybe a Co2 scrubber.
The sealed attic approach ( closed vents) and "tight filled" vaulted rafter spaces appears to be the most effective insulation method for my application from what I've researched, I'm just trying to do it without spending 3500$ ++on spray foam.

And although we have frequent rain, the air/moisture content is pretty low, but that's why I included a (6-8 mil) plastic vapor barrier to prevent in home moisture from creeping into the cellulose and batts.

I'll submit pics when I can
Thanks.
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Old 03-17-2013, 05:09 PM   #5
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This should help on a few points; no cellulose for cathedrals; http://www.buildingscience.com/docum...oss-enclosures

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Old 03-17-2013, 05:13 PM   #6
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my best advice, is to either use spray foam or use rigid foam board with an airspace between your roof deck and insulation. The chances that you are going to get a tight and effective airseal with your ideas are slim to none, and if you don't, its going to have a negative impact on how your home is breathing. Spray foam is your answer if you absolutely want to do the roof deck.

I did spray foam a slate roof not too long ago, and to keep the air flow and circulation, I used 1x2 spacers sistered onto the rafters, and then applied the foamboard to that, and spray foamed over the top. You can do something similar, which will allow the continuous breathing of the roof.

More importantly, if cost effectiveness is what you are aiming for, why not mastic and insulate the ducts, airseal the attic plane, and insulate the attic floor?
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Old 03-17-2013, 05:16 PM   #7
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I'm trying to break down your questions/concerns into more bite-sized pieces, lol. This on required thickness of foamboard to deter condensation in a cathedral, see map pp. 4; http://www.buildingscience.com/docum...n-roof-venting

Code reference; http://www.buildingscience.com/docum...rchterm=attic+

Yet, Oregon has it's own energy/building code, more on that later...

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Old 03-18-2013, 03:54 AM   #8
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Gary in WA,
thanks for the excellent information articles-although I dont think
this article (http://www.buildingscience.com/docum...oss-enclosures) is appropriate considering the design of the 1960'2 leaky house, I can understand why the issues occurred with the warm moist in home air channeling through the 3.5" walls with no vapor barrier and an unknown "pack" of cellulose. The "rule of thumb" for tight pack is IIRC 3.7 lbs/cubic foot, and tight packed into a 10" rafter spaces would be significantly different than the article test home. I would also benefit from decreased air movement/loss and an R value around 36+

This is the article that got me thinking about pulling that 28 yr old R-30 batt insulation out of the vaulted ceiling:
http://www.applegateinsulation.com/P...es/249234.aspx

This vid was also informative:
http://www.drenergysaverct.com/home-...l-ceiling.html


This article fig 2, is the design that I was thinking of originally for the attic ceilings. rigid foam and than batts/cellulose...pick one, I did not know that a fire barrier like dry wall was required, but that would aid in cellulose fill.
http://www.buildingscience.com/docum...rchterm=attic+

This article http://www.buildingscience.com/docum...n-roof-venting
That you posted indicates that I would only need an R-10 in my attic, so any 2" tuf-R foil face from Home Depot would exceed that number-IIRC it has an R 12.8 or something of the sort.



asinsulation
No disrespect intended, but I dont think getting a good air seal using rigid foam and spray foam around it would be difficult....Unless there was some serios ETOH consumption at the time
Using just spray foam at 2+$ a board foot is just ridiculously expensive for a DIY guy like myself and an attic size that I've got..
If only I could get my own equipment and do it myself, but the manufacturers have stymied that with expensive equipment or really expensive little kits, 350+$ for 200 B/F I can get 640 B/F rigid at the Depot fot about 300$
At this point I'm leaning toward your advise:

Quote-
More importantly, if cost effectiveness is what you are aiming for, why not mastic and insulate the ducts, airseal the attic plane, and insulate the attic floor?

With 6" (5.5") floor cavity, I could simple fill in the walk areas with 5" of rigid foam and spray foam the edges for a seal and an estimated R-19, do the insulating and sealing as you suggest and than use cellulose to top off all the low spots, this might be my route for simplicities sake, but I'm still most likely "tight packing" the vaulted ceiling.

Last edited by drgnflys; 03-18-2013 at 11:13 AM.
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Old 03-18-2013, 08:41 AM   #9
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Is the current assembly vented?

You can create a similarly vented assembly and still address the thermal conduction and air tightness.
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Old 03-18-2013, 11:03 AM   #10
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Windows on wash
Yes the assembly is vented, but poorly-I'm going to start tearing down my soffits in a few days to see just how poorly the vaulted areas are vented.
See my 2nd post for a description, I counted 12 small vent holes along an estimates 30ft run, these vents did not align with the rafter vents, and there was probably only a 1/4" x 9.5" of air travel between the vent locations from inide to outside because of the soffit design and rafter interference.
Are you suggesting the inserts that install next to the roof sheathing that allow for air circulation? It would be impossible to get those into the vaulted ceilings that slope away from the central attic-that side is enclosed and some runners eye ball in at about +18'.
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Old 03-18-2013, 11:53 PM   #11
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sounds like you are on the right track.

Just make sure you get a decent machine for your densepacking. Your typical rental will not cut it, and if you are going to attempt this application, you only get one chance to truly do it right or it could be a costly mistake/fix.
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Old 03-19-2013, 07:58 AM   #12
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I am still very wary of dense packing roof structures. Guys that are much smarter than me have tried it and failed.

On way to do situations like this is to drop the drywall and either foam it or create a vented space with rigid foam and some venting channels (also out of foam is best).
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Old 03-21-2013, 01:10 AM   #13
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Sorry, here is the correct one; http://www.buildingscience.com/docum...+in+flat+attic

And another side of it; http://www.greenbuildingadvisor.com/...ack-unvented-c

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Old 03-22-2013, 07:50 PM   #14
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An observation from the second article you postedGary in WA

"The failure mechanism in this project included inadequate cellulose density which allowed for separation of the cellulose from the exterior roof sheathing. During the winter months, the high indoor relative humidity levels diffusional moisture coupled with moist air flow through the loose cellulose allowed moisture to pass through the cellulose and condense on the roof sheathing above and drip back into the cellulose below. The cellulose was not able to dry towards the exterior due to the built up roof above. Nor was it able to dry successfully to the interior due to the elevated indoor humidity levels below. A dozen years later, we should not be surprised that the roof rotted off this building.



My current plan will include 2" of Tuf-R insulation glued to the roof sheathing with spray foam between the rafters, too many people have voiced concerns about moisture build up and rot occurring.... although I live in Portland Oregon where the relative humidity is VERY low compared to the constant rain/drizzle we receive yearly, and I just ran a 6" vent hose out of my upstairs bathroom out of the attic.

I will not drop the ceilings, instead I will pre-foam the rigid insulation boards and than run them into the rafter space and install via 4" or 6" holes drilled into the ceilings for access. The 2" tuff R is rated at R12.8 (or near that) plus roof sheathing and spray foam, and my climate zone 4 requires an R-10 to avoid condensation-so that gives me 30+ % over required R rating, and hopefully this will greatly improve the comfort the home.

Gary I appreciate the input, well, so much that I've just exponentially increased the cost and effort of this project with ceiling work and 31$/sheet Tuf-R insulation.

Thanks all- I move forward in April.
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Old 03-23-2013, 06:10 PM   #15
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Sounds good, see you later...

Gary
PS. may want to check on Oregon Code for your floor joists, mine were over-spanned and had to double them. 30# load w. Doug-fir #2, 16"oc= 10' span; http://publicecodes.cyberregs.com/ic...002_par017.htm

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