roofing question

i am going to be doing a re-roof on my house. the old shingles will not be removed. i am allowed to do one new layer of shingles over one layer of old shingles in my area with my pitch. my decking is in good shape. what length roofing nail should i go with due to the fact there will be 2 layers of shingles on the roof?

 

Strip the old shingles off, never shingle over old. Your township does not know the load bearing of your rafters. Homeowners who request this of me... I walk away.

 

I was hoping to get it done this week but the weather is not cooperating, the extra time may allow me to do that

 

Agrees. Yes it can be done but not ideal. Compete tear off and reroof will last longer then a second layer over the first layer as well.