I am planning to reshingle the front part of our house this summer to
eliminate a couple of random leaks. Despite numerous attempts at repairs, I
haven't been able to determine the source, so I've decided to just tear it
all off and do the absolute best preparation and reshingling I can to fix
it once and for all (basic 3-tab shingles).
Our main roof is 6/12 pitch which transitions to a porch roof that is a
3/12 pitch. I'm planning to install ice and water shield up past the
transition point this time around, instead of the double-coverage roofing
felt we have now. However, one area that concerns me is the actual joint in
the roof sheathing (1/2" plywood) where the two slopes meet.
When I built the roof I used those little metal "H" clips between rafters
for extra support. They work fine on the main roof, but the sheathing still
flexes more than I would like at the transition point. I can't really
install blocking there since I need to maintain airflow for venting under
the sheathing, not to mention it would be a pain to install now.
In Tauntons book "Graphic Guide to Frame Construction", they show an extra
layer of sheathing attached on top, to smooth out the transition for
shingles. It sounds like a good idea, but I'm curious what issues it might
cause. For instance, it seems like the upper edge of the add-on sheathing
would create a "bump" where it meets the main roof. I suppose I could
minimize that by using thinner 1/4" plywood, as this only serves to smooth
and tie together the transition. I also wonder if this would cause issues
at the outer edge where the metal drip edge of each slope meet.
How do you handle this?