1 Literacy rate, adult female (% of females ages 15 and above) 2  Literacy rate, adult male (% of males ages 15 and above) 3  Literacy rate, youth female (% of females ages 15-24)  Literacy rate, youth male (% of males ages 15-24)
Asphalt shingles- 30 yrs. (only about 15 yrs. of life, though). Tin- 50-100 yrs. You do the math. Tin is way more expensive, but usually works out to save you over the life of the roof (longer than yours). For Canadian weather, I'd strongly recommend the tin as it sheds snow/rain better. Oh, I'm thinking NW Canada, not sure where you live, but still, tin is the better material all the way around.
The shingles likely won't last as long, so the job could actually end up costing you more in the long run. The savings simply don't warrant the compromise of quality and potential risks. That said, overlaying asphalt shingles with a metal roof could be an option, provided there is no underlying damage. Metal roofs offer energy savings but do cost more upfront than traditional asphalt shingles. They also last longer and stand up to foul weather better than shingles. No matter what type of roof you choose, make sure you tell your roofer to fix any underlying problems you have before installing any new roof.