1920's Bungalow Shed Dormer

A-Train · 02-09-2009, 02:45 PM

I am looking at adding a Shed dormer to the back of my 1928 Bungalow in Portland, OR. I need to replace the roof anyway, so I was thinking while I'm at it....

Anyway, I have a couple of issues:

1. Upon examing the existing structure of my roof I found I have rafters that are 2x4's on 24" centers. If I add a dormer the full length of the house out the back I will be using 2x10 or 2x12 rafters. The span from the ridge to the exterior wall is about 17'. My question is how do I tie these new rafters into my existing ridge? And, what do I need to do to the side of the house that I am not touching? The roof is not sagging right now, but what do is the city going to require of me as far as supporting that side and more importantly am I going to have to meeting newer insulation requirements? I forgot to mention that the attic is already finished. I could sister in new rafters, but would have more dry wall to take out and I don't know how thick I would have to go to get the R-38 rating that I think they are looking for.

2. My existing roof pitch is 7in12. The new dormer looks like it would have to be a 2 1/2 in 12 to make it worth it. It I want to do comp. roof, am I just asking for trouble? Even if I use a snow and ice shield on the entire dormer roof?

Let me know if you have any thoughts.

Thanks.

scowl · 02-09-2009, 03:20 PM

My shed dormer in Portland is 2 1/2 in 12 and I roofed it with cheap roll roofing 13 years ago and it's still in great condition. Our weather is not hard on roofs that don't leak.

The dormer was built in 1909 and was originally a sleeping porch. It was roofed with, get this, long cedar shingles. Over the decades people threw layer upon layer of roll roofing on the shingles until they and the T&G decking below rotted to dust. I replaced everything except the rafters. They're 2x4's 24" o.c. with a span that you would never get away with now (but they're not sagging at all).

Scuba_Dave · 02-09-2009, 03:36 PM

I used ice & water shield on the entire roof on my sunroom roof & dormer
Despite a lot of ice & snow & ice dams this year no leaks
My small front 3 season porch - no ice shield, tar paper - it leaked

fireman.roofing · 02-09-2009, 04:00 PM

That ice & water shield can get expensive, but it sure does the job!