PVC / Vinyl coated steel roof OPINIONS needed

Hi folks, we got our quotes for steel roof and need your opinion.
The company is Hy-Grade and will instal a wooden grid (sort of like furring) on top of existing ashphalt shingles, and on the grid will put the steel shakes. These are PVC coated and shaped in a way that helps combat metal expansion due to changing temperatures. The metal roof will be about 3" over the existing roof wich allows for air circulation (see image:
http://www.hygraderoofing.com/images/pic_6.jpg ) Apparently leaving old shingles has 3 main advantages:
Sound proofing - Heat control - Moisture control.
The rep assures us that air ciculating between the old and new roof prevents condensation on the inside of the metal shakes. But... The company's 10-point disclaimer devotes 2 points to inform customers that Hy-Grade will not be responsible for damage caused by moisture due to heat loss causing ice dams or condesation and that they will not be responsible for the growth and spread of mould.
I'm wandering if you have any opinions on metal roofing in general and the mentioned disclaimer points in particular.
I will add that the cost of the roofing is 9,000 for Steel vs 4,500 for regular shingles canadian (8,200 vs 3,900 USD), so quite attractive to us given the 50 year warranty.
Thanks!
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snipped-for-privacy@yahoo.com wrote:

I did the same thing but the grid is on top of heavy shake. Works fine.
I put on the Gerard Roof:
http://www.gerardusa.com
Cyprus color:
http://www.gerardusa.com/products/gerardtile.htm
I have the tile style. Only problem is that if you don't step on the wood grid when walking on it you will cause it to dent. They are easy to remove by just removing a nail or two and using a nail bar to pop it back out. However, I see they now have a foam underlay that can be used in areas where you walk.
Being in a frequent hail area I got a 27% discount on my home owners insurance.
I put it on six years ago. Looks as good as the day it was installed.
Can't comment on mold or moisture as I live in Denver, Colorado area. (semi-desert).
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Rich256 wrote:

few weeks ago. he said the price of metal has gone up almost two fold. i could not do it now for the price i did it a couple of years ago.
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below the air dew point. Don't you get dew on cars in the morning? Moisture will definitely condense on the top and bottom sides of the roofing. The roofing has to be installed so that the condensation does not accumulate and cause damage. Proper ventilation, drainage, and water-proofing are required for long satisfactory service.
I had two metal roofs installed and am well pleased with them. As with many things, good materials and proper installation make the difference. Ask for references, preferably older installations, and also look carefully at the workmanship. Don Young
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