I'm just planning to start getting my roof framed up and covered in the next couple of weeks and had a few questions. First, I was reading about using something like Grace Ice and Water Sheild over an entire roof instead of tar paper. Is this a good idea or should I just keep it along the edges and valleys? I'm planning 2lb spray in the ceilings, not sure if I'll go vented or not. Second is shingles. It's starting to get around freezing here and I want to get the house closed in and protected. We get chinooks here where the winter temps can be as high as 20 degrees C and the next day is -30. Should I put something up to protect the roof and wait for a warm stretch or do my shingles in these cooler temps? I don't even know what I could use to protect it, I guess I just don't want to do this twice. Thanks, Sean

sgo79;

the entire roof is adviseable as a secondary water barrier if you live in a hurricane prone area, but it does not seem like thats your case.
i would go with just the edges and valleys

Thanks Chris, I was just checking to see if I had any replies. I'm in Calgary, Canada so no hurricanes here. I was more worried about our crazy winter weather and ice dams. We can have a foot of snow one day, 15 degrees C the next to melt it all and then -30 the next to re-freeze. Maybe I'll just go with the edges and valleys. Thanks again, Sean

With 2lb foam under the roof deck Ice & Snow you'll be sandwiching the roof deck between a class-I vapor retarder (the Ice & Snow) and a class II vapor retarder (2lb foam), with the higher permeance product on the exterior. Odds of ending up with permanently saturated roof decking is high. Use sparingly

Roofing felt is semi-permeable, which does allow outward drying.

2" of XPS above the roof deck and over the eaves is usually sufficient to even out roof deck temps to the point where ice dams don't get started. This can be enhanced with a ventilated nailer-deck on 3/4" thick purlins above the foam layer. Even if you don't add the XPS a ventilated secondary nailer deck on purlins would minimize ice damming, and allow you to put Ice & Snow or impermeable membrane below the shingle, sort of like this:

Snow/shingles/Ice&Snow/1/2"OSB nailer/purlins & vent gap/structural roof deck/2lb foam>>>etc

With the ventilation gap between the purlins the nailer deck drys toward the interior (the purlin gap), and the structural deck dries toward the exterior (also the gap), no moisture is trapped in the wood layers.

(Not the cheapest layup, but it works.)

Thanks Dana, That's what my plans are right now, without the XPS, but the sprayfoam company tells me it's unnecessary to vent. That was leading me into thinking that I could cut out a lot of work and expense by going unvented but after reading your post it makes sense. I think I may be looking for shortcuts just because it's starting to get cold now. I have 16" deep trusses going up, I don't imagine those staple up styrofoam vents would be as good would they?? Thanks, Sean p.s. Sorry I still can't figure out why my posts are one big paragraph when I post.

Sean;

to be safe you could put 2 rows along the eave edge to deter ice dam problems. I grew up in a snow belt area and am familiar with the ice dam problem