Can I extend 1 layer of shingles from 2 layers?

Question

The last time the shingles were redone, the contractor put a second layer over the existing layer. I have a covered porch on the back of my house. There is a bad leak. I need to take off both layers and replace the decking. Can I replace one layer and join it to the two layers of the rest of the house or do I need to replace two layers?

Answer 1

you only have to replace one layer

Answer 2

porch roofs are notorious for leaking due to ice, low pitch and run-off from roofs above.

for quick fix:

2 layers is normal, weave top layer of shingles together to prevent leakage

for more permanent fix:

all shingles would be removed, some rolled roofing with some tar underneath is installed followed by shingles

Answer 3

Yes, you can do that.  It's done all the time with additions/renovations.

Answer 4

Is it asphalt shingles your talking about?  If so you shouldn't have 2 layers, the contractor was lazy and didn't want to strip the old roof, or gave you a great deal on the new one.  And yes you can butt into the existing roof 2 layers or 1.  You should not have 2 layers of shingles!  You should keep an eye on it because it is likely to leak since it wasn't done right to begin with.