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Old 07-27-2015, 06:53 PM   #16
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Sure you can. Only area of concern for me would be the overhangs and fascia boards that will not be as insulated and therefore cold spots.
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Old 07-27-2015, 09:37 PM   #17
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Polyiso ages and losses R-value; to get the safest R-value from it, IMHO- figure R-5 (Implications) per inch; http://www.buildingscience.com/docum...endent-r-value

Reducing the temperature of the first condensing surface (roof sheathing) requires R-25 (5" Polyiso) for your location in Zone 6; http://www.buildingscience.com/docum...rchterm=attic+ This would eliminate any vapor barrier requirement on the sheathing, or under it. The previous answers covered it, I just wanted to point out the vapor barrier as it appears you may still be having difficulty there. Hope this helps you with vapor barriers and your set-up.

Though you can figure it (as said already by 1985) at R-5.6 (to meet code minimum) or 4-1/2"... per your energy requirements per climate Zone 6; http://energycode.pnl.gov/EnergyCode...?state=Vermont

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Old 07-28-2015, 05:51 AM   #18
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Quote:
Originally Posted by Rodney Cox View Post
i appologize for not being more knowledgeable but is there any reason i could not go with 3 -3 inch layers of polyiso with a vapor barrier between the deck and the insulation and then 1/2 inch osb on top and just get rid of all the cellulose if i woulb end up leaving the cellulose wouldnt i have to dense pack it if i just go with the polyiso i should have plenty of r value and as far as looks there is a parapit wall around 3 sides of roof i did a box cornice around it with a small roof with a 3/12 pitch so i can make it look ok even with 9 0r 12 inches on top of deck the place im getting the iso from only has 3 inch thats why i want to use 3 inch for 14 dollars a sheet
There is no reason you can't do as you described. How does the roof drain? if 3 sides have a parapet then I assume the slope goes to the open side and it goes in to a gutter? You would have to stack up 6 layers of 2x's on teh front edge for a nailer so you have a place to attach your edge metal. So keep that in mind there will be extra money in covering that.

Do you have a picture of the area?
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Old 07-28-2015, 08:29 AM   #19
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i will posts some pics in a little bit i am just trying to get the best roof i can without breaking the bank. If i would put the cellulose back into the roof would it need to be dense packed i know it would settle over time and leave a void between the insulation and the roof decking would that cause issues later.I would still put 6 inches of iso on top of deck
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Old 07-28-2015, 08:45 AM   #20
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There shouldn't be a problem with the void. IMO
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Old 07-28-2015, 09:24 AM   #21
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insulating a flat roof


I will attempt to post some pictures later today. My first attempt the pics are posting upside down.

Last edited by Rodney Cox; 07-28-2015 at 09:26 AM. Reason: pictures not posting properly
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Old 07-28-2015, 10:34 AM   #22
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but if i was to leave the cellulose i would have to remove all of it seal the perimeter and where all walls are and any ceiling penatrations such as lights with spray foam then reinstall cellulose
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Old 07-28-2015, 11:06 AM   #23
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another question i will have to buy a heavy duty tarp when i am doing the roof could i also use the tarp under the polyiso for vapor barrier
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Old 07-28-2015, 11:32 AM   #24
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You don't need a vapor barrier in this climate.

Seal up the drywall by sealing up the top plates, box and seal out the can lights, seal up any plumbing vents, penetrations, etc.

I am guessing there is no ductwork in the ceiling but if there is, seal it up well too.

Insulate the perimeter properly and you should be good once the polyiso goes down.
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Old 07-28-2015, 07:45 PM   #25
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RC, I gave you the wrong requirements (good catch, WoW- thanks for PM); yours are R-15 in foam, and R-38 total, cavity fill made with whatever... http://energycode.pnl.gov/EnergyCode...state=Virginia Be sure to air seal the (hopeful) blocking between rafters to stop air/moisture coming up from the brick/wood sheathing on wall void. Many times I see they are not blocked off there as soffit material stops at brick because installed after mason finished (easier not to cut top row of bricks to below soffit/rafters). The warm/moist air permeates the brick after a rain and sun drives moisture through to required void space behind brick. Just a quick check with hand over the wall from inside as this would allow moisture to your exposed rafters. http://www.buildingscience.com/docum...n-brick-veneer

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17,000 dryer fires a year, when did you last clean the inside of the dryer near motor or the exhaust ducting?
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Old 07-29-2015, 07:03 AM   #26
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Should i use a open cell or closed cell foam for air and moisture sealing in attic space or does it matter. So I need to take out cellulose foam where all walls meet ceilings foam all lighting and other penetrations through the ceiling and go around entire perimeter foam all exposed brick in attic space and rafter ends where they contact brick
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Old 07-29-2015, 07:30 AM   #27
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Most folks will specify closed cell foam when it comes to this application in roof assemblies. Closed cell is far less vapor open than is open cell foam. While I agree, the most important aspect of the air sealing in this case would be to stop the airflow and both open cell and closed cell will do a fine job of that.
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Old 07-29-2015, 08:15 AM   #28
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My wife tried to post pics. Everytime they post upside down any ideas
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Old 07-29-2015, 10:46 AM   #29
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Posted pictures in different albums see what you think it just shows how i did the top of the parapet walls and the existing metal roof i am going to figure out exactly what i need and post them with the steps i need to do for the roof then if you all can look and make sure i am not overlooking anything i would appreciate it Thank you all for all the good info
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Old 07-29-2015, 11:14 AM   #30
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Another question I want to screw 1/2 inch osb over top of polyiso I found some 8 inch screws for a good price just wandering how many i need and what the screw pattern would be for this
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