Roof tear-off versus 2nd layer

Gurus:
This summer we plan to replace our 24-year-old shingled roof with long-lasting dimensional shingles. The old shingles are still in pretty good shape and the house has had no ice damming problems.
Contractors are pushing two schools of thought for the old roof. 1. Tear it off and put down ice and water shield before putting on new roof. 2. Shingle over the old roof and utilize the old flashing.
Which process would you recommend for the longest-lasting roof?
Thanks for your thoughts.
Tom Milwaukee, WI
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snipped-for-privacy@sbcglobal.net wrote:

in the short-term.
You want the longest-lasting option, you go with option #1.
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Tear-off is double the price in my neighborhood. The best way to do it obviously, but much more expensive.
If you are planning on living in the house for another 30 years, tear off is a good way to go.

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snipped-for-privacy@sbcglobal.net wrote:

That is the only option if you want a long-lasting, leak-free roof job.
If cost isn't an issue, ask your contractors about options for upgrading the roof covering - such as tile over a modified bitumen underlayment system. Good for 50 years or more if done right.
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There is a benefit to tear off. The roof deck is exposed and any problems solved. TB
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while i agree, option 1 is the 'best'. but if your roof isnt leaking now, if you factor in price vs how long it will last, you may find option 2 may be viable.
i am also assuming that there is only one layer of roof already (i.e. hasnt already been reshingled over another layer). if there are multiple layers already, tear it down.
lastly, if you want the longest lasting roof, i'd go with a metal roof.
randy

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I've lived in a house long enough to do it both ways. The first time was putting one on top of the other. For the next 12 years, we lived with little leaks showing up and having to repair them. one leak got so big, we ended up with mold and a $40,000 repair bill. Thank goodness for insurance. Some will say we must have had a shoddy job. I don't think so. It was done with 40 year shingles by one of the better known companies in our area. Its just that the old roof was not a good foundation for putting on the new one.
When we re-roofed, we tore everything off and put down all new sheathing. The roofer told us that roofing companies had abandoned the practice of putting one on the other and building codes have changed in many areas so its not allowed.
In my book, your option #1 is not even an option for any length of time. You paid the money for a house. The price of maintaining it properly is not cheap.
Bob
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snipped-for-privacy@sbcglobal.net wrote:

Just a thought. My roof was hail damaged. The insurance company agreed to a replacement. One of their requirements was a tear-off. They would not cover the new roof without the tear off, which they were paying for. They thought it was worth the cost. I sure was not going to disagree.
--
Joseph Meehan

26 + 6 = 1 It's Irish Math
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My vote is for #1. It makes for a lighter, stronger roof in the long run. Layers of shingles can make a roof sag.
On 2 Mar 2005 12:40:54 -0800, snipped-for-privacy@sbcglobal.net wrote:

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Covering over a roof is still accepted by building codes as a viable an
useful option and shingle manufacturer's accept the process as well.
If an interior and exterior inspection of the roof sheathing yields n problems, there is little reason to rip off and replace the existin layer.
Replacing your automobile tires if you get a flat is also an option i you can afford it
-- manhattan4 ----------------------------------------------------------------------- manhattan42's Profile: http://homerepairforums.org/forums/member.php?userid=4 View this thread: http://homerepairforums.org/forums/showthread.php?tu89 This post was submitted via http://www.HomeRepairForums.or
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manhattan42 wrote:

There are two very good reasons to remove the existing layer of a shingled roof.
1) To reduce the weight of the roof covering. The roof structure may not be designed to carry the weight of two layers.
2) Primary weatherproofing comes from the bottom underlayment felt, which ages and becomes brittle. Just the act of walking on it and nailing an additional layer of shingles may cause it to crack, which raises the risk of water intrusion and ice dams.
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John Willis wrote:

It is true that the exposed roof surface (ie. shingles, tile, metal, whatever) will deflect the majority of the water. But wind blown rain will get under this surface, and that is where the underlayment comes into play.
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John Willis wrote:

I guess it is just semantics, John. Most roofers I talk to refer to the underlayment as the 'dry in' or primary protection and the final covering as secondary.
In the case of tile or metal coverings the underlayment is a two-ply or greater system that provides virtually all the waterproofing protection - since even heavy rain will run over the sides of the tiles and onto the underlayment. The tile / metal keeps the UV off the underlayment and extends its life.
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On Fri, 4 Mar 2005 08:13:06 -0600, manhattan42

So far as I know, National Building Codes allow up to three roofs on a house. Just because it is up to code does not mean it is ideal. A house with more than one roof installed is more likely to develop leaks (because the roof exposed to the weather is not installed over a uniformly smooth substrate) and I've never seen a second roof like this last as long as it should. In every case I've seen, a house with a second, third (or more) roofs installed require attention far sooner than they would if there had been only one roof.
The only reason to roof over an existing roof is because of money. It takes more time and labor and dump fees to remove an existing roof. Sure, it is up to code. Sure it is common practice. Yeah, it is cheaper. Is it best practice? Nope.
-- John Willis (Remove the Primes before e-mailing me)
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John Willis Wrote:

But that is not the observed fact by shingle manufacturers nor the Cod agencies. There is no more lilkelihood that a covered roof will fai prematurely than one over a fresh substrate all things being equal.
Which is why manufacturers offer FULL warranty of their products an Code Officials allow the practice.
Likewise, I have NEVER seen a second layer fail prematurely in my 25 years as a professional contractor simply because it was a second o third layer. If they failed, it was due to issues completely unrelated to the numbe of shingles.
So just because one rips off and installs a primary layer instead o installing a second one only does not guarantee that the job will b surperior and justify the added cost. Especially if half the time onc the roof has been ripped it has been found that the paper and plywoo is in good condition and didn't need it in the first place.
Yes, the issue is money, and more often than not it is money th contractor wants to needlessly put in his own pocket at the expense o a gullible homeowner
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manhattan42 wrote:

But, there's the rub...all things are <not> equal between the two cases...
If the old roof is in reasonable condition and there's no underlying other fault, yes, a 2nd-layer roof may last--but that's far from the case many times.
I'm seeing a real trend in insurance companies here to not accept the 2nd-layer owing to them having seen higher costs in subsequent years on previous work....to me, that's pretty conclusive--they've got probably the best database in existence on the actual cost and aren't known for being extravagent in making settlements.
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manhattan42 wrote:

Unless your house was built before there were building codes that required good nailing of the sheathing, and you want to renail to prevent the house from coming apart during the next hurricane (Florida) or tornado (almost anywhere).
Unless you want to put down secondary waterproofing, or an ice-and-water shield layer.
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On Fri, 4 Mar 2005 14:08:49 -0600, manhattan42

Just because Code says something does not make it true. A laminated, dimensional, five and five eighths inch exposure shingle, such as GAF Timberline, installed over a five inch exposure wood shingle roof will have leaks before an identical installation, except where the substrate is smooth decking instead of wood shingles. Why? It has to do with how the exposure of the faces of the different materials align with each other. In the first example a careful observer will notice horizontal waves across the plane of the roof-a kind of frequency based on the difference in the exposure of the different materials. Those waves represent areas where leaks are likely because the top shingle is not flat, in fact it is somewhat dish shaped across its horizontal axis, which means water tends to travel a bit farther on that horizontal axis in those areas. If fasteners or the butt ends of the shingles happen to be in the wrong place in those areas, leaks will happen, and they will happen more quickly than they would if the installation had been over a smooth deck. Why? Because over a smooth deck that water would not have had the ability for that horizontal travel as all the shingles lay flat and none are dish shaped. Physics is physics and nothing code or the manufacturers say will change that fact.

Code allows lots of things I personally wouldn't do when building my own house. Just because it is supposedly safe and code allows it does not mean it is ideal or can't be improved upon. As for the warranty, in these cases the shingles haven't failed, the installation has, so of course the manufacturers don't care if you install a second roof over a first. All they warrant is the shingles will last a certain length of time. They don't warrant anything about the installation!

All the above that I've written is also based on over 25 years of professional experience in the field of residential roofing and roofing contracting. BTW, if a three tab shingle is installed over loc-tab shingles, it gets even worse and I've seen examples of this kind of installation fail in as little as five years. The best solution in those cases is to remove all the roofs and start fresh again.

This much is very true. In fact I would rather have an excellent installer put on a second roof than a poor installer put on a first!

If you get good performance from installing a second roof over an existing roof, good for you. I've found that it is always better to tear off a roof and start fresh.
-- John Willis (Remove the Primes before e-mailing me)
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===========================I have to agree with you....but that does not mean that I did not save a few bucks, (a good thing)...and save a hell of a lot of Time & work removing the original roof...(both good things) when my original roof needed replacing...
Next time (if I live so long) everything will be removed and I will still save a lot of time and Money..since I will only be writing the check not doing the job myself...getting too old for that kind of work...
Bob Griffiths
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Phisherman wrote:

metal shingles. i paid just 1/3 more than 40 year reg shingles.
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