It’s 90 degrees out and all I can think about are ice dams
I am planning on doing some second floor / attic insulation upgrades to my cape cod house. It was built in the early 80’s with the second floor construction consisting of 2×8 rafters at 16” o.c., 2×4 knee wall at 16” o.c. and 2×6 rafter ties at 16” o.c. w/ ½” sheet rock on the interior of all of this. The 2×8 rafters have R-25 batt insulation from the knee wall up to the rafter tie’s, the 2×4 knee walls has R-13 batt and the 2×6 rafter tie’s have R-19 batt. I have a continuous ridge vent in place and 2” dia. circle vents at the soffit for each rafter bay.
As the case in most cape cods, the rafter insulation between the knee wall and rafter tie is crammed in and no ventilation can pass thru.
So here is my plan:
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Remove the existing sheet rock an batt insulation between the knee wall and rafter tie.
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Run 2” Dow Tuff-R from the soffit up to the ridge leaving a 1 3/4” gap between the insulation and the back side of the roof deck.
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Add un-faced R-13 batt to each rafter bay from the soffit up to the ridge.
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Add 2” of XPS rigid foam to the back side of the knee wall.
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Add R-25 batt rolls to the space above the rafter ties perpendicular to the rafter ties.
Is this overkill? Or could I get away with using rafter vents that staple on and R-19 batt rolls? Or do I need to insulate the entire rafter bay as long as I fix the area between the knee wall and rafter ties?
I had ice dams at all of my gutters this past winter and never seem to have any snow accumulation on the outside of the roof above the rafter tie line or below the knee wall line.
Replies
rug.
No snow, down low-seems there's heat escaping into that space from kneewall to outside wall. What's the insulation in the floor/ceiling area?
Any penetrations from your exterior wall through the plates? Any sheeting on that floor portion?
Slow movenent of heat from that source could migrate up and then melt snow up high, while still venting the rafter spaces.
I'd look down low for starters.
I think there is insulation in below the second floor plywood deck as there is insulation peaking up between the outer edge of the plywood deck and the plate the base of the rafters are nailed into. To what extent of the insulation, I am not sure. Right now pulling up the plywood in this area (the triangle area between the deck, knee wall and rafters) is not in the plan, or budget.
I also have 4 (2 in each of the bedrooms on both sides of the house) - 3'x3' plywood doors w/ some sort of rigid insulation on the back side.
I am also looking into replacing these plywood doors with some sort of proper insulated door.
Insulated doors are good.......
But air-tight is the ticket. Warm air entering from around the perimeter and / or through those "doored" openings could be your sole source of cause for the melting snow and resultant ice forming.
I know taking care of the perimeter is not in the plans, but if all the other work you plan on choosing might be compromised by what you don't do.
Best of luck.