I am extending the length of my back porch and therefore the roof over
it and am thinking about the roofing(asphalt shingles).

I figure I can tuck the last new row of shingles up under a row of the
existing house shingles. But I'm wondering about a good way to weave
the new rows of shingles on the new part of the porch together with the
rows of shingles on the old part of the porch.

Does anyone know a good technique or a good reference book that might
cover it?

Thanks.

RonT

Two problems- doubled starter course, and nails.

Normal practice is to double the first course for consistent thickness,
avoiding gaps in coverage, whatever. You're talking adding a course
under that.

The existing shingles are nailed down, making it difficult :') to slip
shingles underneath.

Dunno what you mean by "weaving"- is there a valley?

New courses you're talking will start from bottom (I hope), and you're
hoping that x courses will sync with the existing. Maybe.

Do you want this to look good, or like an obvious cheapie job? The old
shingles will _not_ match the new.

Not being a pro, nor Holiday Inn Express resident, I can see a real
mess, and redo, in the offing. IOW, I'd tear the old off.

HTH,
J