1 roof or 2?

I am about to have a new asphalt shingle roof put on my house. It now has one asphalt shingle roof on it and the decking underneath is in good shape.
Other than it costing a little less by saving on the tear-off process, is there any real difference between ending up with one roof or two?
Even if it costs more, if there is an advantage to having the present roof taken off first, I would do that.
Thanks.
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On Thu, 28 Sep 2006 09:16:49 -0400, "BETA-2K"

Not much difference IF the original roof shingles are stll very flat and not starting to curl up.
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Where do you live? Does it get below freezing in the winter much?
I'm in nothern Illinois, USA. One reason I did a tear off vs nailover was to get the iceguard sheeting that provides a lot better protection against ice damming than otherwise. It's code here now, but wasn't done on roofs 10 years ago. Another reason is that there were some small signs of water penetration on the house when we purchsed it, and given I wanna stay here awhile, I wanted to make certain there was no rotting or anything more going on with the roof decking.
There are other modest advantages to a tear off which are hard to quantify. One of which is that you'll have a lot less weight on your roof. Not a big deal, it's surely designed to hold it though. The second is that the new shingles are working on a much flatter surface, so they'll look better in the case where you have any curling occurring on your first layer. Finally additional layers can harbor additional moisture. Whether either of these "soft" peace of mind issues will amount to any real increased risk of water penetration over the life of your new roof is probably debateable at best.
Personally I feel it's just technically a lot cleaner to do a tearoff. However, if you don't plan to stay in the house very long and can put the delta in $ to better use elsewhere, a 2nd layer isn't necessarily a bad thing thing, though buyers may look slighly more favorably on a tearoff vs a 2nd layer.
Best Regards, -- Todd H. http://www.toddh.net /
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A couple of things to consider. How long will you be living in the house? If you plan to retire there and live long enough to need another roof, it may be better to pay the extra now for a tearoff than in 20 years when you have limited income. If you plan to sell in just a few years, having a good, new, single layer is a good selling point.
If the existing roof is in good condition and flat, you will see no difference in the finished roof. If it is curling up, or otherwise physically damaged, get it off.
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BETA-2K wrote:

Yes, roof should last a lot longer if you do tear-off first. Also have flashing replaced as needed, and consider gutters if they are getting old.
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So long as the old roof is just ageing and not having problems with quailty, then the gains to be made with a tear off simply aren't worth it. Go ahead and apply a second layer of shingles, there will be a very small decrease in the life of the second set but that will be more than ofset by the saving in istallation.
But if the fisrt layer of shingles is failing due to poor istalation or damage or somthing like that, then ext layer will also suffer from those things and fail prematurely: in that case you really ought to tear it off.
John
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BETA-2K wrote:

I'd probably leave it up to the roofer. Usually you do not tear off existing shingles until 3rd roofing job because of weight. But if your existing shingles are badly warped and you are putting on a single colored untextured shingle, it may show through. Frank
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BETA-2K wrote:

First, if you leave the present shingles on, there's the question of knowing for sure there isn't a spot or two where the decking maybe isn't as good as you think...
Second, while a lot of roofs are put on w/ two or three or even more layers, it isn't the manufacturer's recommendation and may shorten or limit warranties and is generally known to shorten expected life span of the new roof.
My opinion is that you're putting on a new roof and to skimp is in the "penny wise, pound foolish" category.
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BETA-2K wrote:

It is becoming increasingly uncommon to put multiple layers of shingles on. Most contractors insist on a complete tear off these days and cannot guarantee the results otherwise. I have never installed new shingles over old but have torn off a lot of multiple layer roofs.
One advantage of a complete tear off is that the roof deck can be inspected and repaired. It is common that the deck is rotten in places especially where multiple layers are present. then you can start from the deck up with a clean, dry, and sound surface.
I bet most jobs that include multiple layers these days are done by the homeowners or family members who just want to get it over with and don't have the time or energy to tear off and clean up all that material. Tear off and clean up can be a much bigger job than installing the new material. It is a huge part of getting the job done correctly
Lawrence.
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On Thu, 28 Sep 2006 09:16:49 -0400, "BETA-2K"

Any chance of a heavy snow in the next 20 years?
If so, then rip off the old roof because of the increased weight. Removing a couple of tons of roofing from your roof might make a difference.
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BETA-2K wrote:

I'd leave it and use the money saved to put in gutters - or some other upgrade.
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Thanks to everyone. I thought I posted a response last night but I don't see it here.
The short version of what I tried to post last night is that I will probably just go ahead and have the tear-off done before the new roof goes on. Overall, that seems like the safest bet although I can see good reasons for doing it either way.

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If you end up re-covering, make sure your contractor has _all_ the flashings properly re-set or replaced. Tom BETA-2K wrote:

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