Roofing over old roof


I am probably obsessing over this, but if I do decide to roof the back-half of my existing roof, what criteria do I use to decide whether I can roof over the existing shingles or not?
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red spake thus:

1. How many layers of shingles are already there (there's a limit to what any roof will support).
2. What condition the top layer of shingles are in.
3. Whether you want to do a half-assed job or not.
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David Nebenzahl wrote:

The original roof was put on in 1970. The south half was replaced by the previous owner about 1993, being stripped down to bare deck. The north half, being in decent shape, was left alone at that time.
Now the north half is on it's last legs. Obviously it needs to be replaced, otherwise, I wouldn't attempt it. So, I would be putting another layer over one existing layer.
I'm a 42-year-old woman who will be helped by her 18-year-old son ( I hope). We did the shed roof last summer/fall with eight bundles and it was pretty rough going, especially hauling the bundles up to the roof, but I am highly encouraged by the fact that we have had two solid months of rain and no leaks on the shed.
So, I'd like to avoid the extra work of tearing out the old shingles if possible. On the shed, we just roofed over the existing roll roof with three-tab shingles, and except for one row where my son forgot to stagger the shingles, it looks great.
So, what specifically do I look for to decide if going over the top is "doable."
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In many places, you can get rooftop delivery of shingles. Might be worth checking.

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red wrote:

Generally I would say you can roof over one layer of roofing if it is flat and in generally good condition. If it is curling or starting to fall apart I suggest taking it off.
Stripping it all also gives you a chance to evaluate the condition of the deck as well.
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Joseph Meehan wrote: Generally I would say you can roof over one layer of roofing if it is

Lots of the granules are off the shingles, and the shingles at the bottom edge are pretty curled down, otherwise, it seems pretty flat. Maybe I'll try to take a pix and post if the weather ever drys out here.
The shed roof was roll roofing and was perfectly flat and in excellent shape when we re-roofed. And since a couple of roofers had told me it was ok on that roof to go over the existing shingles, I didn't question it on that job.
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In my county, you can have up to 2 layers of shingles according to code.
You should check your local building codes to make sure that 2 is allowable.
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IMHO:
Most limiting factor, check your local codes. Some juridictions do not want fire fodder too thick on your roofing.
Then have a roofer/engineer check your attic for proper support. A roof does weight a lot. ;)
Just my guesses.....
tom @ www.FindMeShelter.com
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