Cathedral ceiling insulation... zone 6 WYOMING

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Cathedral ceiling insulation... zone 6 WYOMING

Postby emcdonnel » Sun Dec 25, 2011 6:30 pm

Merry Christmas!

Santa would't even land on my roof last night, because there was no snow for his sleigh. This is because i have no insulation in my roof...

I own 1.5 story house in Northern Wyoming (zone 6). The upstairs rooms have ceilings that slope with the roof, so it is called a half story, but could also be considered a cathederal style ceiling... The tallest point in the room is 7 feet tall, and sloping to a few feet at the room edges. The house is Lath and plaster, built 90 years ago. The roof leaks, so it is time to redo shingles. please help guide me through the process of insulating while I have things torn off...

Here is what exists: From the sky towards the inside of the house.

T-Lock shingles
Ceder shake shingles
Older ceder shake shingles
Toung and Groove 1x4
2x4 rafters with gray dusty old insulation inbetween
Lath and Plaster

Since i am planning to pull the shingles down to the Tounge and groove, i would like to add insulation to the exterior of the house. I will be using metal shingles (gerard canyon shake) screwed to 2"x2" boards that run horizontally. To add insulation under this, i could screw 2"x3" boards vertically to the rafters with 2" extruded Polystyrene foamboards between them. The horizontal boards and the shingles would screw to these 2"x3"s, leaving a 1" air space to keep the shingles cold and prevent ice dams. It would look like this from sky down...

Gerard metal shingles screwed to
2"x2" battons screwed to
2"x3" battons with
2" EPS between
sitting on roofing paper
on the tounge and groove.

When (in a year or two) we tear out the lath and plaster, i'll be insulating the inside of the house. Will this work?

The bottom of tounge and Groove is visible from inside the room.
add paper faced fiberglas between the 2x4 rafters, cover it all with 2" expaneded foam (my vapour barrior) and then 5/8ths inch drywall with 3 inch screws going through the EPS?

What i dont know about is this vapour stuff. It seems like the cold roof is a no-brainer (ice dams otherwise), and I need more insulation, but am i making a tripple vapour barrior? Will i get condensation between the EPS and the roofing paper inside the house, and or condensation between the roofing paper and the XPS outside the house.... I would only be getting R-33 of the suggested R-39 for my zone. any help?

Cost is a major issue as well, but I dont mind labor. If you see a problem with my idea, or a much better solution to my problem. please write!
thanks in advance,
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Joined: Sun Dec 25, 2011 5:51 pm


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