How To Look At A House
McGarry and Madsen's home inspection blog for buyers of
site-built, mobile/manufactured and modular homes
What is the average lifespan of a metal (galvalume) roof?
Saturday, August 25, 2018
The expected lifespan of a metal roof is 30 to 50 years in Florida, with an average of 40 years. Although sometimes called a “tin roof,” the most common metal roof material we see in this area is galvalume, which is a steel sheet with an electrolytically-applied coating of a combination of zinc and aluminum to extend the lifespan. It is manufactured in many different profiles, including corrugated, standing seam, 5V-crimp, and PBR, to name just a few; and can have a clear or painted finish. Galvanized steel metal roofing, which is an older type no longer used for residential roof, has a shorter lifespan.
This graph compares the average lifespan of a metal roof to other roof types:
The average lifespan estimate is based standard metal, which is 26-gauge, and “average” conditions. Many factors contribute to a longer or shorter life of the roof; so a particular metal roof’s life can vary—sometimes significantly—from the average.
Here’s a list of conditions that affect roof longevity:
- Thickness of metal - 24-gauge metal, which is thicker, will have a longer lifespan. Lighter gauge metal, such as 28 and 30-gauge, are typically only used to agricultural barn roofs and have a shorter expected life.
- Color of roof - A dark color painted roof absorbs more heat, and the paint will oxidize sooner.
- Angle of roof slope - Higher pitch roofs tend to last longer.
- Proximity to Ocean - Salt air mist accelerates the corrosion of metal roofing and manufacturers’ warranties have exclusions for installations near salt water.
- Orientation of roof surface - A roof slope facing south will get more sunlight, and have a shorter life.
- Quality of roof material - “Economy” roof materials have a shorter life.
- Installation - Sloppy or improper installation shortens roof life. Manufacturers typically blame the roofing contractor for a roof that has a short life, and they are sometimes correct. Exposed fasteners, over-driven fasteners, and poor or missing flashing at valleys and edges will shorten the roof life.
- Attic ventilation - An unventilated or poorly ventilated attic reduces roof lifespan.
- Trees near roof - Tree branches rubbing on a roof or the acidity from the accumulation of leaf debris on a roof shortens its life.
- Harsh climate - Severe weather, both harsh winters and hot summers, along with big temperature swings within a 24-hour period, also shorten lifespan because of the expansion and contraction of roof materials.
Metal roofs begin to corrode as they age and, when spots begin to pit and rust through as in the photo below of an extremely old galvanized steel corrugated roof in Cedar Key, the roof is at the end of its lifespan.
Go to our blog post What is the average lifespan of the parts of a house? for rating of other house components. To understand the basis, potential use, and limitations of lifespan ratings, see our blog post How accurate are the average life expectancy ratings of home components? Are they actually useful?
• • • • • • • • • • • • • • • • • • • • •
Field Guide for Home Inspectors, a quick reference for finding the age of 154 brands of HVAC systems, water heaters, and electrical panels, plus 210 code standards for site-built and manufactured homes, and the life expectancy rating of 195 home components. Available at amazon.com for $19.95.
• • • • • • • • • • • • • • • • • • • • • •
To learn more about roofs and attics, see these other blog posts:
NOTE: These life expectancies are based on data provided by InterNACHI, NAHB, FannieMae, and our own professional experience. Because of the numerous variables that can affect a lifespan, they should be used as rough guidelines only, and not relied upon as a warranty or guarantee of future performance.
of Blog Posts
Top 5 results given instantly.
Click on magnifying glass
for all search results.
Buying a home in North/Central Florida? for a team inspection by two FL-licensed contractors and inspectors. Over 8,500 inspections completed in 20+ years. In a hurry? We will get it done for you.