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Old 04-20-2010, 10:51 AM   #16
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Great thanks for the response. So it would be wise to go with the closed cell. That is probably the max I can get do to the 2X6 framing.

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Old 04-20-2010, 11:19 AM   #17
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yes but use dense-packed. 3.5 lbs/cu ft. be sure the install the correct amount
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Old 05-21-2010, 08:58 AM   #18
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Ok I think I figured out the plan. How does this sound. I am going to do the spray foam on the main living ceiling. With only the 2X6 rafters and a tricky roof to vent it seems the most logical. I can get a high R value. The spray foam will be sprayed down to the kneewall only to keep costs down. Not sure how long i'll be there. I will use foamboard and foam to seal all the floor bays below the kneewall prenting air from moving from the cold vented area to the non-vented living space area. I will build up the attic/eave floor to allow me to get an R36-38 of cellulose. I will lay plywood to use for storage (leaving large gaps). For the kneewall, I was thinking about on the attic/storage side using rigid foamboard, cellulose, and then the poly vapor barrier. That will give me more R value in the kneewall. Does this sound like a plan? Am I taking the right approach? As you all know I am trying to do it right yet keep the costs down. That spray foam is expensive to have installed.
Also, using the cellulose how do I fill the wall cavities? just make a slice in the poly to put the hose in?
How do I know if I need a poweredvent for the unvented eave portion? Is there a telltale way to find out?
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Old 05-21-2010, 09:31 AM   #19
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venting will determined by these factors... your climate, amount of snow allowed to build up on the roof and if you used ice and weather shield on the eave of the roof, and your internal temperature settings. What is needed is that the roof surface does not reach dewpoint.

The walls. Use Tyvek and not poly. Slice and fill and tape with cellulose.
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Old 05-21-2010, 12:04 PM   #20
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Just for clarification, your suggesting using tyvek on the part of the kneewall facing in towards the living space? Or facing the vented portion? I was going to use foam board to give it extra r value on the back side?
secondly, all i do is slice the poly or tyvek and fill with cellulose? where do you make the slices at the top or bottom of the stud bay?
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Old 05-21-2010, 12:12 PM   #21
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tyvek is not needed if you are using foam on the back side. But you can use this or poly on the inside to hold the insulation. Slice at the top, the ins. will fall to the bottom and then seal.
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Old 05-21-2010, 01:28 PM   #22
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Hey Bob,
Thanks for all the help. Not to sound like an idiot, I just like to cover all the bases to make it easier was I get going. So would you attach the foamboard with the adhesive thats made for the board? Then staple the poly on the inside. Make a slice at each stud bay and then fill each with the cellulose? Any specific tape? any thing else I should do or look out for?
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Old 05-21-2010, 02:25 PM   #23
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I would use drywall screws and a roofing washer to attach the foam board, in the climate it will exist adhesives will eventually fail. Use Tuck tape which is made to splice the poly. duct tape will also fail in short time. The main thing to watch out for is the air sealing to the floor and above and below the knee walls are 100%. I assume you are using closed-cell foam for the rafters. If you have an attic access it also must be sealed and insulated the same as the floor. Build a box with foam and attach with magnetic tape or buy access insulated hatch kits that are readily available. If you are foaming around recessed lights be sure they are the correct type or cover with sealed 14 X 14" foam boxes first. Use flashing and fire rated caulking or sealant around any chimney chases.
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Old 05-21-2010, 07:24 PM   #24
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I can't thank you enough for all the info. It really is a big help. I am going to make sure that above and below the knew are air tight. The closed cell will go down to the kneewall so that should be air tight. Below like I mentioned I am planning on using foam board between the bays and then using the can foam to seal all the edges. Should be air tight and I will make sure I focus on that area.
I did contact the manufacture for the lights and like you mention then said not to use the foam around the lights. They said to either use your method or to wrap them in 3" of fiberglass and have the foam sprayed up to the batts.
So for the walls, what thickness of poly is recommended? Once I make the slots in each stud bay how much should I will it? Will it buldge?
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Old 05-21-2010, 08:09 PM   #25
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use 6 mil to help avoid the bulge. You will use about 2.5 lbs / sq ft in the walls for loose fill cellulose. Add strapping if you have a problem with bulging, but you shouldn't.
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Old 05-22-2010, 11:49 AM   #26
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For the foam board in the rafter bays and the back of the kneewall, regular 1/2 sheathing foam board will do the trick right? R3
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Old 05-22-2010, 04:32 PM   #27
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yes as long as all edges and seams are sealed well
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Old 05-22-2010, 09:59 PM   #28
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Very good advice from Bob. OP, to help you understand: http://bct.nrc.umass.edu/index.php/p...-smart-choice/

Page #9, kneewalls: http://www.karg.com/pdf/Insulaton_de...and_Biddle.pdf

When using strapping, never leave an air gap from it between drywall/insulation for convective currents. Probably less for horizontal furring installation, though. The insulation should always be in contact with the drywall/v.b. (if used). As Bob said, cellulose will stop the air movement in the insulation, but air movement is possible at the furring (which could negate the R-value of insulation before the heat reaches the insulation) unless drywall is sealed: http://www.buildingscience.com/docum...wall-approach/

Bob, what are your thoughts on this? http://www.applegateinsulation.com/C...id=249418&fd=0

Be safe, Gary
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Old 05-23-2010, 07:54 AM   #29
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GBR.. A good way to go. I am not an advocate of poly for walls since it is nearly impossible to get or maintain the barrier 100%. This option will yield a better solution. The interior air movement within the walls and floor joists are what is normally missed in construction and is where all the energy loss occurs. Fiberglass with no air sealing is the culprit. When drywall panels are not glued the edges you introduce another weak spot in the system which this paint does not address. So proper construction and/or correct air sealling retro-fit is still the only complete solution.
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Old 05-24-2010, 09:37 AM   #30
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Tons of great info. So Bob, if you don't like the poly, what would you use on the walls? Do you like the spray foam insulation in general? Questioning if I should go with the spray foam on the walls too. If I don't do you recommend using the can foam to seal the gaps in the sheathing boards, , 1X8? before putting in the loose fill/fiberglass?

When putting in the cellulose if there is no soffit vents do you put the instulation all the way over into the soffits?

And lastly (sorry) If you do not have a face for the insulation, you need to use the vapor barrier paint on the ceiling below? What if half the ceilingis under the vented section and half isn't?

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