Urgent roofing questions

I have a friend who is trying to decide on what type of new roof to get & needs some input from roofers and/or manufacturers.
Project history:
The current roof is 3 layers of 3-tab shingles on a '79 double-wide. There is sagging (some severe) of the decking. The third roof is only 2 years old, but is already stressed & shows sympathetic cracking from the deteriorated shingles below.
The last roof was done by a friend (not a contractor) as a birthday present.
She has had several roofers out & has been told that they can install a new metal roof over what's there now; and she's been told, by another contractor, that he will take off 1 layer of shingles & install the metal roof.
My observations:
1. I believe the decking has deteriorated to the point that it needs to be completely replaced (part must be because of water damage) because it will be impossible to properly install shingle or metal with the sagging & waving.
2. If a metal roof is installed over the existing roof or over the roof with 1 layer of shingles removed, the condition of the decking is such that within 1-5 years, the screws, nails, or whatever is used to anchor the metal, will release & allow the metal to act like a wing & begin to tear itself apart in a windstorm.
3. It appears that there are several places where there may be fascia rot and/or rotted rafter ends, behind the vinyl siding & gutters.
My recommendations to her:
a. Remove the existing roofing & decking, repair any rotted fascia boards and rafters, re-deck & install new roofing of choice over that.
b. I advised her that she was wasting her money and that any manufacturer's warranty would probably be void due to improper installation - if the substrate was not repaired.
Where she is now:
She's got different roofers telling her their work/product will solve her problem.
She's got family & friends giving her different advice & guidance.
Your help is requested:
If any roofing contractors and/or manufacturers would care to reflect on this post, she's agreed to follow your suggestions.
Thanks
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On 8 Aug 2003 13:51:15 -0700, snipped-for-privacy@bellsouth.net (Tom Baker) wrote:

I agree with TB, and in fact, effective this year (January 2003) New York requires that no more than two layers of roofing materials may be on a roof for fire safety reasons. I can't find a citation, but my recollection of the rationale behind this regulation is that it is twofold: to force people to tear off the original cedar shingle roofs which were on many older houses (pre-WWII) and are fire hazards as well as to prevent people from putting too many heavy layers of roofing materials on housing structures that may not be able to handle them (post-WWII). So now roofers in this state have to do more tearoffs, a big reason for roofing prices going up. I had to tear off three layers from my roof this summer before redoing the decking, etc., but I would have done that regardless of this law because it's the right thing to do to get the best possible roof.
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snipped-for-privacy@bean.rochester.rr.com wrote:

Not to mention the added weight of wet snow in New York.....
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On Fri, 08 Aug 2003 11:38:37 +0000, W.E. Co wrote:

I would just like to point out that the roof could be strapped/firred, making the existing deck superfluous for a metal roof. That being said, the existing roofing and deck is a substantial weight that I wouldn't want over my head.
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On 8 Aug 2003 19:35:15 -0700, snipped-for-privacy@hotmail.com (W.E. Co) wrote:

SNIP
Consider that standard 3 tab shingles weigh between 200 - 250 lbs. per 100 square ft. then add snow ice etc. I don't how trailers are built there but I would hate to be sleeping under all that. Louis
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snipped-for-privacy@hotmail.com (W.E. Co) wrote

If you had two layers already on when your current roof was installed, you've probably got the original shingles that came on your mobile home.

You are probably right on-point here. Of the mobile homes that we have re-roofed, the majority of the older ones have CDX plywood down as their decking. This is generally the lowest grade a lumber yard sells.

I doubt that it will take 5 years for your problems to start showing up. I don't know where you are, but you mention wind storms, so you must get some good ones every now and then. If the wind hits your roof at the right angle, it will be like sticking a piece of tape to a playing card - it will lift it right up if it's not properly installed to good decking.

If you don't fix your rotted areas now, they'll continue to rot behind your metal/vinyl fascia.

If you don't do it now, it will cost you 3-5 times as much to repair down the road.

Yep, and it's too late by then. The other replies to your message are right about the weight of your roof. If your decking is in that bad of shape, it's just a matter of time before somebody falls through or part of it falls in.
I wouldn't let any more estimators on there, they can take their measurements from the ground. Find somebody you feel you can trust - check their references & ask to see work they've done on other mobile homes.
Keep in mind that the more layers of shingles, the more nails & the longer it takes to tear off. With the added caution of bad decking, it could effectively double or triple the normal roofing time.
Don't let anybody put a metal roof over what's there now - tear everything off, replace your decking with the next thicker decking (what you've got now could be 3/8" material), repair any rotted framing or fascia, then put your new roof on.
Hope this helps.
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Granted, though I would tend to refer to it as the accepted grade, not necessarily the proper grade for roof decking. I prefer to think of CDX as crating grade.
Anything we do over 24" centers is at least OSB or BC grade. The adhesive, strength & integrity of better than CDX just gives us piece of mind that we can't find in CDX.
Several years ago, we did a roofing sub that included the decking. The contractor provided the materials, which turned out to be CDX seconds. The SECONDS notation had been stenciled on the edge of the strapped skids, but not printed on the face of the sheets. We never noticed it on the ground & the general had it re-stacked & lifted to us on the rafters.
Sometime during the first year after the new owners occupancy, the plys de-laminated & bubbled - had an interesting design, but the owner wanted flat.
It cost us almost $5,000 to defend against that, even though all documentation showed that the only responsibility we could be held liable for would have been the installation of the decking & the roofing, if there was a problem there.
In 1997, we re-roofed 12 units in a trailer park. All of those trailers were trussed on 24" centers & 2 of them had 3/8" plywood, the rest were 7/16" CDX.
Five of those, including the 2 with 3/8" decking had to be re-decked because of de-lamination. We recommended re-decking all the trailers, but the owners didn't want to, so they signed a release.
Since our court experience, if CDX is spec'd, we don't want the job. If the owner of general won't upgrade to OSB or BC, we'll substitute at our cost or refuse the job.
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On Tue, 12 Aug 2003 00:42:48 +0000, Paul Nelson wrote:

Guy, your wasting money. BC stands for the veneer grade. One side B, the other C. If your looking for strength check the span stamp on the plywood. A brief explanation of the stamps can be found here:
http://www.beconstructive.com/consumer/article_plywood.asp
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