Pros and cons of installing a roof on top of another or stripping the old roof off first?

Question

which is better and why? 1. Remove existing shingles and start fresh

2. Install the new roof on top of the existing roof.

I will be installing architectural shingles on top of 3 tab shingles or on top of the original decking

Answer 1

Nail-over pros:

Cheaper, faster, cleaner, easier, less chance of leakage during installation, and a minimal added R-value.

Nail-over cons:

Twice the weight, and the next time you will have twice as much to tear off.

Tear off pros:

Better looking job, and you know your doing it right.

Tear off cons:

Possibility of water damage inside the house, because it's sure to rain as soon as you get the roof halfway torn off.

Which is better? Of course it's better to tear off the old first. (The exception to the rule would be when installing a metal roof over shingles.)

In my opinion, based on observations over many years, a nail-over roof does not last as long as it would normally. Not sure why, heat build up between the layers? Moisture?

Answer 2

Better to remove old shingles why add the extra weight to your roof.  Less chance of developing leaks later on.

Answer 3

If your present roof doesn't leak putting new shingles on top of the old won't "develop new leaks later on."  Your roof will easily handle two layers of shingles but you will find if you try to hire somebody they will almost always want to remove the old shingles and start fresh.  If there are any old shingles curling or deformed your new roof will not have a smooth appearance but if your present roof is in pretty good shape and you can smooth out any curling shingles by nailing them down there shouldn't be any problem adding a second layer.  It is much less work now to not remove the old shingles, but it will be harder when you reroof in 15 years or so to remove two layers rather than one.

Answer 4

hmm tough choice good luk

Answer 5

we have been installing new shingles over old ones for years and have no problem. You have to use arch. over 3 tabs. Make sure your 3tabs are flat if the curl up the new ones wont lie flat causing a roof leak. By keeping the old ones on it gives you a additional water barrier just make sure you dont have soft or damaged plywood. If a roofer advises you against it its usually becaus he wants the extra work of removing the old one but there is no need for that.