Shed roof additition

[cmsilvay]

We are planning a 12ft bump out on the side of our 14x28 little house.  It has a 12/12 roof and the boys have been using the loft but how fast they grow and they would like to be able to stand up LOL.  My question is, has any one else done this and did you cut and strip in to old roof or did you put a nailer into the rafters and lap the sheathing and lace the shingles. I will be adding extra footings and doubling the rim joist on the existing building and building a pony wall from the top of the existing exterior wall to the new rafters to transfer the load to  the ground so the portion from the existing roof to the pony wall will not support much weight. The shed side would be a 4/12 pitch. My plan was to strip the shingles and put a nailer(header)then angle cut the new rafters and secure them to the nailer. I didn't plan on removing any sheathing and then lapping the sheathing, papering and flashing then lacing in the shingles. The addition will run almost the full length with the back part being a bedroom and the front part being an enclosed porch.

[Bob S.]

Here in Boise, Id. years ago (back in the early 80s) we had a family that died in a house fire. In the investigation they figured the fact that the house had been remodeled (similar to your plan) was a contributing factor. The fire burnt in the dead space crated by leaving the sheeting of the old roof.

[Don_P]

I think we need to research that more. My gut tells me compartmentalizing a space is going to slow a fire down. I am required to put in access if there is more than 30" of headroom if memory serves. My guess is that if the undetected fire above them was connected to the entire roof the result probably would have been as bad. I need to read those sections of the code more.

Next, in a truss talk taught by a state college prof he demonstrated what happens engineeringwise when we don't sheath that area. Leaving it as 2x's unbraced in the 1-1/2" direction. The roof weight above tries to make that area rotate and fail. At least in a truss it is usually intended to be fully braced on the top chord. In a rafter the physics of that aren't going to change, there is more meat there but I sheath it. I have drilled 2- 4" holes per bay to connect to venting at times. There's the flue 

[Bob S.]

   In has been a long time since the fire I referenced in my prior post.
   If I remember correctly the problem was that the house had been remodeled mutable times and there where several roofs.This made the fire vary difficult to extinguish.
   I do not know if it caused the deaths.
   It makes seance to me that the roof will be a lot stronger if the sheating is left on the old roof.

[cmsilvay]

I would strip the old shingles off the covered portion right before I weathered in the new roof. The way my luck goes if I stripped and cut into the roof monsoon season would move in as soon as I opened it up then I would fall off the ladder and wind up busted up while its raining in my house LOL.
My mail question is mating the new and old. I did a bunch of truss additions in my younger days and we would stick frame the rafters from the old to the knew laying plywood strips where the jack rafter would meet the roof, This spread the weight if the jack didn't land on a truss/rafter. In my case the the pony wall would support most of the load.

[Don_P]

Well, we just got the foundation in, I stepped on a leaf covered rock and my foot is purple from calf to toes... so yup, sound logic  .
I've always applied a ledger of 2x for the rafters or jacks to land on, even in those "California" valleys. But yes your pony wall is likely taking just about all of the load from that end of the addition.