I think it was command a few years back
anyone still lay a second layer of shingle over one layer?
I have one layer of the flat 3 tab shingles, no leaks only hail damage

perfectly acceptable to do 2 layers.

Most insurance companies will not cover a roof with 2 layers. The shingles get damaged easier with 2 layers.

I always thought of that as one of those issues that will either cost you something now or later. Sooner or later you will probably want to do a tear off back down to the decking. After a hail storm an insurance company will only pay to tear off one layer.

Also, if you ever want to sell your home an inspector will point that out to a prospective buyer, and some people don't want that extra weight on the roof.

Don't do it.

Besides weight, I have noticed that when on a roof w/ 2 layers over time the nails will back out. I think it has to do with improper ventalation. I have a theory on that.

Just put on a metal roof.

Thanks for the info
It is coming off,
found better pricing with better shingles
I roofed it myself last time, getting 2 old to throw a layer on
And it needs to be complete by may

Just saw this thread, good job of tearing it all off.

FYI, most insurance companies will pay to tear it all off, down to the decking, atleast while I was adjusting. Alot of people with older houses have shingles over wood shake over plywood, and unless you have Super Discount Insurance from the hood, they should pay if you file a claim to get it all removed. Now if you change providers and your agent comes out to look at your house and sees several layers, that may or may not be a problem. Honestly, I don't know why they wouldn't cover it, because by not, they aren't going to make any money, as well as starting off on a bad foot with the customer.

Get a load of this one...

2 layers are acceptable and any one that says differently doesnt know what they saying. Now is it better to do a tear off before laying the second layer of shingles, yeah if you want to spend the bucks for the tear off, otherwise a second layer fine. Its more than 2 layers that isthe no no.

I had one in NJ w/ 8 layers

will it hold the weight yes, Will nails back out over time yes. Devil Horse its just not good, if you look at roofs that have two layers and there over 5 years old half have problems.

i didnt say its best idea, but it will work and is an acceptable, widely used process. Nails pop usually because the right length wasnt used.

I don't consider it "acceptable" and I bet most people looking for a house don't either. You save a little cost for a drastically shorter roof life, that's not acceptable to me.

Demolished houses with up to 5 layers...sucks. Let's stick to one layer folks.