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Old 12-26-2007, 11:51 AM   #1
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Attic ?'s


I have a cape cod home in Minneapolis, MN that the attic upstairs is finished. This was done w/o a permit by the former owner, so it was not done right.

The problems I am having are:
1. In Winter, it will not retain heat well.
2. In Summer, it will not disburse heat well.
3. Drywall tape is cracking and peeling

I have removed the drywall from the knee wall on the North Side of the house, which had R11 insulation behind it and the underside of the roof was covered in frost and the insulation (blown type) along the bottom side of the wall was wet. When I looked up at the angled wall above the kneewall that went to the peak, there were duravents installed in the joists and the bottom of the insulation was wet and frozen. There is NO soffit venting or roof vents in this section of roof or a ridge vent. The upper section appears to have 2 passive roof vents, but I am not even sure if these are hooked up. On the 2 gable ends, there are 2 vents just below the peak that are a maybe 2x2 inches.

My Wife and I would like to fix this problem and are looking at insulating the area as in this picture on the right side, but since we have not soffit, we cannot put in soffit vents. Our questions are:
1. What level/type of insulation should be used on the underside of the rafter from the roof/exterior wall up to the kneewall?
2. Same for the area from the kneewall to the peak?
3. What should be do for ventilation in the lower section of attic?
4. We would also like to try and open this area up and are wondering where one might find codes that would help is determine the span of header required to open some of these areas up?

Thanks,
Devin
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Old 12-26-2007, 02:03 PM   #2
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Attic ?'s


The attached thumbnail shows the ideal venting situation. If your gable ends indeed have nothing but 2" vents - that is not near enough. Think of the insulation as an envelope around the heated space. Outside of that envelope should be free air flow. Many people mistakenly think less air flow in the outside envelope is better, and that's why you have moisture intrusion and frost inside inside those areas.
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Old 12-26-2007, 04:39 PM   #3
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Attic ?'s


Look at Air Vent and/or Smart Vent. They have vented drip edge products that would replace your current drip edge. I personally am not comfortable having gutters installed with these products but they are proven methods of venting in situations like yours.
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Old 12-26-2007, 05:12 PM   #4
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Attic ?'s


not to thread jack. but what is the best way to insulate between the angle roof inside and the roofing deck. my space there is 2x6.
any ideas
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Old 12-26-2007, 06:23 PM   #5
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not to thread jack. but what is the best way to insulate between the angle roof inside and the roofing deck. my space there is 2x6.
any ideas
2x6 is not enough for ceiling insulation. You should fur out the 2x6 with a 2x4 to have enough space for R-30 or R-38 insul. and venting baffles. Tie the two together with wood or plywood gussets so the drywall still has a solid "rafter" to be hung on.
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Old 12-26-2007, 06:38 PM   #6
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thats what i would do but the space is just like the pic. above in the thread. the inside is a finished room. and bath with 3 closets.

spray foam?? i have been reading alot about foam but havent tryed.
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Old 12-26-2007, 08:12 PM   #7
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Blow in cellulose if you have access, it has a higher R-value per inch than fiberglass. Still need to maintain an air gap.
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Old 12-27-2007, 02:28 AM   #8
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A few things. It sounds like you have a massive air leakage problem along with inadequate ventilation. First you have to increase the size of your gable vents. Easy thing to do. You need 1 sq ft of net free venting per 300 sq ft of attic floor. The 2X2 things arent just going to be enough.
About the kneewall, was this area used for storage or no. The frost you see there on the rafters is caused by warm air leaking from your living space that condensed there with no where to go. Venting thru bigger gables will help some but since you have no soffiit vents you must try to stop the air from getting there as much as possible in the first place.
When you look at the back bottom of the kneewall where it meets the ceiling joists is this area open or blocked off? How much blown cellulose is there? It should be 12 inches at least and the joist bays should be blocked off with foamboard cut to fit and airsealed with sprayfoam. If this area isnt airsealed its an enormous air leakage point that will bypass all your insulation increase heating costs and can cause that frost you see.
In a general sense to answer your questions:
1. If not used for storage there should be NO insulation on the rafters here. Only insulate/airseal the back of the kneewall and the bottom portion/ceiling joists; insulation should follow your living space/air barrier only. If you put something here you will probably increase the amount of frost as warm air will condense there. The kneewall must have all penetrations sealed with sprayfoam or caulk. Use R13 with the paper facing the living space. Next cover the whole back of the kneewall with 1 or 2 inch pink foamboard. This will give you a R18 or R23 wall system which you need since the back of it is exposed just like the upper attic area and cold wind washing against fiberglass will lower its R value. You can use R19 but you should then again cover the back of the wall totally with an air barrier like tyvek housewrap. Make sure all seams are either caulked, sprayfoamed, or taped using appropriate tape.
2. On the slope portion you can keep the vents but pull the fiberglass if you can. I would blow in dense pack cellulose here instead of FG.

3. Increase size of gable vents and while you are there blow in more cellulose....oops thought you meant the peak. Since no soffits cut down on air leakage by really airsealing kneewall/joist bay junction area, increasing cellulose on ceiling joists, and making an effective wall system behind the kneewall described above.

4. By opening up i assume you mean to use this area for storage? If so it has to be sealed and insulated differently. Air barrier and then insulation will follow the slope and the kneewall will have nothing and be inside the thermal evelope. I can describe it in more detail later if you want but this reply is aleady super long.
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Old 02-18-2008, 10:02 AM   #9
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Attic ?'s


Sorry for the delay in responding.
1. We are in the process of installing an exhaust fan to help remove the stale air and reduce the humidity in the house.
2. I looked at the two venting options and I do not think these will work,as one is for the foundation and the other looks like it requires me to remove the shingles.
3. I am working with an architect on figuring out what I need to do regarding the rafters to be able to remove the knee-wall. Once that is done, I am trying to figure out the best way to insulate the roof, since it was not build as a true "venting roof/cool roof". I am looking at the option of using a hot roof due to the issues with lack of fresh air exchange and also space issues, but would welcome any input. Shingle warranty is not a consideration, as I am not sure what type they are.
Thanks,
Devin
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