My neighbors Matt and Candra have a classic bungalow in Historic West Asheville and last Summer they were looking to replace their asphalt shingle roof. They preferred the look of a metal roof and they wanted to harvest their rainwater with a catchment system (metal roofs are better for rain catchment systems because they don’t shed ballast, asphalt and fiberglass fibers into the water tanks like asphalt shingles).
They received several estimates and considered 3 different options:
1) Asphalt Shingle roof
Life Expectancy: About 20 years.
Pros: Reasonably priced. Fairly reliable.
Cons: Not the look they wanted. Not ideal for rain catchment systems.
2) Standing Seam Metal roof.
Life expectancy: 35-40 years!
Pros: Very attractive, with the longest life expectancy. Good for water catchment.
Cons: Twice as expensive as other options!
3) Exposed Fastener Metal roof.
Life expectancy: 10-35 years
Pros: Attractive and affordable. Good for water catchment.
Cons: Un-predictable life expectancy with a mixed reputation depending on which professional you talked to.
Matt kept thinking about the Exposed Fastener Metal Roof (Option #3). This is also called a “fasten down” roof because the screws are fastened right through the metal panels into the roof sheathing. The critics of this roof say that during the freeze/thaw cycle the metal panels move and corrode around the screws where the water can enter. Some of the roofing contractors Matt talked to refused to install them because of call-backs.
Matt was about to give up on the Exposed Fastener roof when he spoke with Asheville Roofing Contractor Francisco Luna who said that the Exposed Fastener Metal Roof was his favorite option for the money but it had to be installed correctly. Francisco’s crew pre-drills holes into the crimps of the panels. The crimps are the high points of the panels so if there is corrosion around the screws over time, it is unlikely that water will get under the panels (see diagram below). He said that if the panels are fastened at the crimps instead of the flat areas homeowners can expect an extra 10-20 years of life expectancy.
This was a bold claim but it made sense. This was also consistent with my experience in living in Central America where tin roofs are very common. The metal roofing panels were ALWAYS fastened through the high points, not the troughs. I looked through several installation guides for these products and I discovered that the best practice is to install the screws at the high points just like Francisco claimed. So why are so many roofers fastening the panels in the flat/low areas? The answer is upsetting. It’s simply easier and faster to ‘screw-down’ the panels in the low areas because no pre-drilling is needed. This practice is convenient and profitable for the installers but a huge inconvenience for the homeowner when their roof leaks after 10 years!
After a lot of research, Matt and Candra decided on the Exposed Fastener Metal roof pre-drilled and fastened through the crimps (Installed by Francisco Luna’s crew. See photo below). It looks great and they are looking forward to 25-30 years of a solid roof over their heads.
Note: Metal Roofs get an even longer life expectancy when they are coated with a high quality paint and re-coated every 10 years or so.