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-   -   Unvented Attic with fiberglass insulation (http://www.diychatroom.com/f103/unvented-attic-fiberglass-insulation-126561/)

hartkem 12-13-2011 08:31 PM

Unvented Attic with fiberglass insulation
 
I recently bought a house in Kansas city that was built in 2002. It is of the cap cod style and is 1.5 stories. I spent some time investigation how the house was built and what insulation was used. The two bedrooms upstairs which have slopped ceilings and knee walls don't seem to be insulated correctly. The cathedral ceilings has 2x6 rafters with r30 insulation in them. There isn't any air space between the sheathing and the insulation. The insulation is faced toward the warm side but no extra vapor barrier was installed. I assume the entire roof is insulated this way. I don't notice any wrong and didn't see any mold/condensation issues on the sheathing but I don't think this is the correct way to insulate. Also the rafters are insulated behind the knee walls along with the knee wall itself. I though it was supposed to be one or the other. What problems are caused by having both insulated?

Ron6519 12-14-2011 08:19 AM

In a 2x6 joist space, you can properly fit an R-19. Putting more in doesn't improve the insulating factor.
The facing is the vapor barrier.
The insulation should be in the knee wall and the floor behind the knee wall.
With the insulation crammed in there, you don't get any air flow under the roofing and sheathing. This will accelerate the deterioration of both as well as trapping super heated air in the crawlspaces behind the knee wall.

cbaur88 12-14-2011 08:21 AM

I recently bought a house in Kansas city that was built in 2002.
Congrats:thumbsup:

The cathedral ceilings has 2x6 rafters with r30 insulation in them. There isn't any air space between the sheathing and the insulation.
I may be misunderstanding but usually you don't want an airspace w/ fiberglass. You want that flush against whatever you insulating to avoid air pickets. However when insulating the rafters a ceiling of an attic I believe it's usually done in conditioned attics.
The insulation is faced toward the warm side but no extra vapor barrier was installed.
Is the insulation faced or unfaced? If faced which way is the paper facing? Not sure about needing an extra vapor barrier


Here's a link w/ some info: http://www.wilwaylumber.com/howto/in...n/howto086.htm

Snowdog 12-14-2011 04:46 PM

Quote:

Originally Posted by Ron6519 (Post 793731)
In a 2x6 joist space, you can properly fit an R-19. Putting more in doesn't improve the insulating factor.

You are saying that R19 insulates the same as R30? I have R30 in a ceiling the same description as the OP and it made a world of difference.

hartkem 12-14-2011 04:54 PM

The insulation is faced towards the warm side. There is no additional vapor barriers installed. I went outside and walked around the outside of the house today and did not see any vents under the eaves. Per Ron6519's reply the house is insulated incorrectly as I thought. What he is saying is that R30 is only as good as R19 when is is compressed to fit in a space to small. 2x6 is really only big enough for r19. Since this house is so new do I dare remove all the ceiling drywall to fix this? This would be a big job. Maybe I should inspect more for signs of moisture/mold from improper ventilation. Based on my findings I could then decide what to do. It has been this way for 9 years with no problems that I can see so far. What would you all do?

Snowdog 12-14-2011 07:03 PM

I understand, I was wondering why they would be the same. I am learning a lot from here, thank you everyone.

How long until you need a new roof? If it is soon maybe wait till then and address the issue from topside? I will be replacing my roof this coming summer and will likely remove the plywood from there and install some sort of ventilation that way. A lot less messy than going the drywall route I think.

Ron6519 12-14-2011 07:27 PM

Quote:

Originally Posted by Snowdog (Post 794135)
You are saying that R19 insulates the same as R30? I have R30 in a ceiling the same description as the OP and it made a world of difference.

That is not what I said.
I said that you cannot cram an R-30 insulation batt into a 2x6 joist bay and expect to get an R-30 result.

hartkem 12-14-2011 09:15 PM

I will do more investigating on the insulation when I get some time. In the meantime I would like some opinions on what to do about it. Leave it alone or go through a major project of opening almost every cathedral ceiling in this 2800 sqft house.

Ron6519 12-14-2011 09:24 PM

Quote:

Originally Posted by hartkem (Post 794330)
I will do more investigating on the insulation when I get some time. In the meantime I would like some opinions on what to do about it. Leave it alone or go through a major project of opening almost every cathedral ceiling in this 2800 sqft house.

I would confirm your statement about having an R-30 in a 2x6 space to begin with.
Then, I would research what goes where in your locality.

Gary in WA 12-15-2011 09:49 PM

Is there continuous ridge vent? Is the roof deck insulated? Describe the intake/exhaust vents....

Gary

hartkem 12-16-2011 08:34 PM

After some intense investigation I have a lot to update you guys on. First off to answer garys question about the venting. There isn't a ridge vent only pod style vents about every 2 foot close to the ridge. There are no gable vents or soffit vents anywhere. Now back to the issue with the two upstairs bedrooms. I found that the builder did indeed use 2x6 for rafters. Behind the knee walls he insulated both the rafters and the knee wall along with the floor. I removed the insulation from the rafters and there were hundreds of flies all huddled together tying to stay warm. Also I found what looks to be dried up black mold on the sheathing. It is spotty and does not scratch off easily and I have never seen this on new OSB. Now to the bad part. Standing behind the knee wall I was able to pull the r30 insulation out of the rafters above the conditioned area of the bedroom and found condensation and moisture along the rafter closest to the rake wall. Now I either have a roof leak or it is condensing, I'm guessing the latter. I did see that the builder was smart enough to fur out the 2x6 studs with another 1.5 piece of wood but did not leave any room for ventilation. It looks like I should remove the ceiling drywall from the two rooms. Remove the 1.5" furring strip that the builder used and add a 2x4 to the bottom of the 2x6 rafters. Then install plastic or foam baffles to the roof sheathing and reinstall the r30 bat insulation. I will then add some soffit vents. The tricky part will be the other side of the bedroom where there is a dormer window. I guess I will deal with that when I get there.

Gary in WA 12-17-2011 10:48 PM

I would figure out the venting before pulling any drywall. You could also use a conditioned attic at the cathedrals if local AHJ permits; http://www.buildingscience.com/docum...rchterm=attic+

Venting: http://www.buildingscience.com/docum...n-roof-venting
I added gable-end-attic vents for cross venting of my craftsman 1-1/2 story. Just air seal the knee-wall attics from the sloped ceiling conditioned ones. Then vent the top attic by itself. The 2x6 would need furring to new R-values. Pull the f.g. on the sloped rafters in knee-wall attic. Close off the joist cavities under them, add a housewrap, etc; http://www.simplesavings.coop/simple...ee%20walls.pdf

Gary

hartkem 12-20-2011 08:49 AM

I have removed the fiberglass from the rafters in the knee wall area. I now have the floor and knee wall insualted. For the cathedral ceiling rafters I am still trying to decided if I want to do vented or unvented. If I go the vented route and fur out the 2x6s more than an inch the ceiling will start to interfere with the closset door trim. I would then need to move the knee wall inward to maintain the height of the wall. If I went the unvented route I could use spray foam and not have to fur out anything. I would then cross vent the knee wall attic and upper attic above the room with gable vents. I know I would need to use closed cell spray foam to prevent condensation. I can pull the fiberglass out behind the drywall through the knee wall area. Is there a way to spray the foam without removing the drywall? Im thinking is will need to come down regardless.

shazapple 12-20-2011 09:09 AM

Vented would be the proper way to fix this problem. The procedure you typed up in post #11 would be ideal.

Alternatively, if it would be cheaper, you could tear off the shingles, add strapping, a new deck, and new shingles to give the required ventilation. You could even add rigid foam below the strapping to add extra R value. This is referred to as a "vented over-roof" in GBA's article.

hartkem 12-20-2011 09:54 AM

2 Attachment(s)
I thought I would post some pictures to help everyone understand. One is of the knee wall attick and the other is of the ceiling of the room. I am also considering rigid foam.


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