Shingle re-roof

Hi Guys:

First time on here. I have been doing residential shingles for longer than I like to admit. Have a question that in 30 years I still can't figure out the best practice for. When reroofing only one half of a twin house. The shingles run all the way through(no fire wall). What's the best way to join the new side to the existing side? The new side will be ripped off.

Thanks much to all that replied. I'll take all of your suggestions into consideration when I start.

Inspect the condition of the existing roof and roof deck for numer of roof layers, soundness of roof decking, smoothness of existing roo, and other factors that determine whether or not you can do a roof-over or if a roof shingle tear-off is required.

The only way to keep your roof dry is to keep them seperate from the neighbors and cap it like a ridge. That way the roofer that does the neighbors will not screw up your roof.

If it is a townhouse built in the 70's or newer there is a good chance we will just pass on it. They use fire rated plywood. That means it needs to be replaced. The neighbors plywood will be shot to. If we are not doing the neighbors, we will not do the roof.

What i do is first start the tear off at the tie in.

i carefully flatbar the neighbors shingles up being careful not to hurt them while removing their fasteners that tie into my roofing im replacing.

then weave my new roofing back into the neighbors roofing.

I've done a couple over the years where I step flashed the old and the new up the center of the fire wall and counter flashed with a "U" shaped flashing to slip over the top of both rows of steps. This protects your work when the neighbouring unit gets their roof done.