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Old 12-14-2009, 09:07 AM   #1
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Cape Style Home Insulation - Kneewall


I have a Cape Cod Style home (built approx 1980) in MA. I'm looking at having my insulation re-done.

Therre are insualtion batts blocking the rafter space from the kneewall to the main attic so the air cannot easily get from the kneewall soffits to the ridge vent. I'm looking at re-doing the entire attic inuslation (blown in cellulose) but want to address the ventilation first.

Should I:

1. Remove the insulation batts from the incline going up to the main attic (approx 6 ft)? If so, what do I replace them with while still allowing airflow?

2. Leave them alone and concentrate on more blown in insulation.

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Old 12-14-2009, 12:03 PM   #2
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Cape Style Home Insulation - Kneewall


Slide foam insulation vent forms between the joists against the plywood on the roof. This will allow enough air flow where it is needed. Then leave existing knee wall insulation and add more blown insulation as you want to.

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Old 12-14-2009, 12:19 PM   #3
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Cape Style Home Insulation - Kneewall


thats what i was thinking too. the only issue is that it is tough/nearly impossible to insulate that slope. I wont be able to add batts under the baffles because there is only a few inches of space. therfore, i wouldnt have a vapor barrier on that area. If I tried to blow insulation into that area under the baffles, i risk clogging the space between the two baffles (i need two baffles to get get from the kneewall up to the main attic area.
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Old 12-14-2009, 02:26 PM   #4
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Cape Style Home Insulation - Kneewall


Pull the old batts. The foam baffles tend to rip when they snag on the nail points above. You could use the H.D. brand for the same price, that have 25% more air space: http://www.bergerbuildingproducts.co...sAccuvent.html Or Lowes special order: http://www.adoproducts.com/provent.html All plastic and a much stiffer back (first one given) to counter the blow-in cellulose. Install one most of the way then add the other with a few inches overlap and tape them together as the required 1" gap between would not pertain here. And just paint a vapor barrier primer on the ceiling drywall area: http://www.panhandleinsulation.com/b...materials.html Use the old batts to plug the cavity's other end when installing the cellulose with the extension nozzle.

Be safe, Gary
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Old 12-14-2009, 03:35 PM   #5
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Cape Style Home Insulation - Kneewall


good plan.

another question:
under the kneewall is open space between the 1st floor ceiling and the kneewall floor (which is just planks). When I was loking at someone doing this for me (may do it depending on cost), they were proposing to "drill and blow" into this area instead of blowing the insulation onto the kneewall floor. The benefit (i think?) is that they wouldnt need to add baffles on the soffit side of the kneewall because the insulation would be blocked off by the top plate of the first floor ceiling and be under the kneewall floor.

what are your thoughts on this approach? would you do the baffles anyway?
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Old 12-16-2009, 03:07 PM   #6
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Cape Style Home Insulation - Kneewall


The baffles stop outside air (from vents) from infiltration the edge of the insulation over the outside wall/ceiling line. Many people read baffles, and stop there, without adding the Windblockers. Older houses seldom installed blocking under the knee wall, as now required for fire code. That joint is very important to stop air infiltrating: http://www.homeenergy.org/archive/he...95/950309.html http://www.simplesavings.coop/simple...ee%20walls.pdf Yet, isn't there a warmed room below?

The best way (without spray foam) is: http://www.homeenergy.org/archive/he...96/961110.html
Another reason to block air from the insulation: http://www.homeenergy.org/archive/he...92/920510.html
On the sloped ceiling, add rigid XPS boards, then drywall to get your assembly required R-value there. http://www.coloradoenergy.org/procor...f/r-values.htm No thermal bridging of the roof rafters.
Just be sure to air seal and maybe vapor barrier--- almost as important as insulation and ventilation.
Be safe, Gary

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Last edited by Gary in WA; 12-16-2009 at 03:10 PM.
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