Washington · Metal vs asphalt
Metal roof vs asphalt shingles
Asphalt costs less today and lasts about 20 years on published averages; an Interlock® aluminum roof costs more today and is built to be the last roof you buy. For a house you'll keep, compare both written prices over the years you'll own it, counting the next asphalt replacement.
Reviewed by Scott Plumptree, Director of Marketing, The Interlock Group · Updated October 7, 2026
Asphalt
About 20 years
NAHB / Bank of America study, 2007.
Aluminum
Known to last over 100 years
A property of the metal, not a promise.
Washington
3,219 Interlock roofs since 1997
From our job book.
Side by side
| Asphalt shingles | Interlock® aluminum roof | |
|---|---|---|
| Life expectancy | About 20 years (NAHB / Bank of America, 2007) | Aluminum has been known to last over 100 years; a property of the metal, not a promise |
| Material warranty | Varies by brand and line; read who the warrantor is | Guardian Lifetime Limited Material Warranty: material and finish, original purchaser, transferable once |
| Rain | Granules wash off and shingles curl and crack as they age | Absorbs no water and can't rot |
| Moss | Moss holds moisture and can lift shingles so water gets underneath (OSU Extension) | Moss can settle on a shaded roof, but there are no shingle tabs to lift and nothing to rot; keep it clean |
| Wind | Tabs can lift and blow off in winter windstorms and coastal storms | Panels lock on four sides; wind warranted to 120 mph when installed to manufacturer specification |
| Snow | Holds snow | Sheds snow; snow guards planned where slides would land |
| Salt air | Granules and tabs weather on exposed waterfront and coastal roofs | Aluminum has no steel to rust |
| Weight | Heavier per square foot than aluminum | About 0.41 to 0.59 lb per sq ft installed, by profile (ICC-ES ESR-1790) |
| At the end | Torn off and sent to landfill, then replaced | Aluminum is recyclable |
| Up-front price | Lower | Higher |
Asphalt life expectancy: National Association of Home Builders and Bank of America Home Equity, Study of Life Expectancy of Home Components, February 2007 (a US study; local weather, design, material quality and maintenance all move it).
Homes in Washington that replaced their roof with aluminum
Recent Interlock® roofs installed in Washington by our own company. Tap a roof to see all of its photos.
Is a metal roof worth it in Washington?
The honest answer depends on how long you'll own the house. An asphalt roof costs less today and will be torn off and replaced, likely more than once, while you live there. An Interlock® aluminum roof costs more today and is built to be the last roof you buy.
The way to decide is with real numbers for your house: get a written asphalt price and a written Interlock® price, then compare them over the years you expect to stay, counting the next asphalt tear-off and replacement. We'll give you ours in writing after one visit.
When asphalt is the better choice
- You plan to sell within a few years and the buyer won't pay for the roof.
- The roof's slope is below 3/12 (every Interlock profile needs at least 3/12).
- The budget today simply doesn't allow it, and the current roof can't wait.
If you're replacing asphalt now
Many of the roofs we replace in Washington are asphalt. A single layer of asphalt can be roofed over only if our inspection finds it suitable; otherwise it comes off, along with any soft decking the inspection finds. Ice dams are a separate question from the roof covering: they come from heat loss and ventilation, and ice damming is a stated exclusion of the material warranty, so we look at your attic with you.
Questions, answered
Is a metal roof better than asphalt shingles?
For a house you plan to keep, usually yes: a metal roof absorbs no water, has no shingle tabs for moss or wind to lift, sheds snow, and outlasts asphalt, which a 2007 NAHB / Bank of America study put at about 20 years. Asphalt costs less up front.
How long do asphalt shingles last in Washington?
Published averages put asphalt shingles at about 20 years (NAHB / Bank of America, 2007), and local weather, design, material quality and maintenance all move that. Washington's long wet seasons, moss under the trees, winter windstorms and, on the water, salt air work on asphalt every year; Oregon State University Extension notes that moss can lift shingles so water gets under them.
Will moss grow on a metal roof?
It can, on any roof that stays shaded and damp, according to Oregon State University Extension. On aluminum there is no wood to rot and no shingle tab for moss to lift, so keeping the roof and gutters clear is cleaning, not repair.
Is a metal roof louder than shingles?
Installed over a solid deck and underlayment, as residential Interlock® roofs are, it isn't the drumming of bare metal on an open-framed barn.
Does a metal roof increase home value?
We don't publish a number for that; it depends on your market. What a buyer gets is a roof that won't need replacing and a Guardian Lifetime Limited Material Warranty that transfers once.
Can a metal roof go over asphalt shingles?
Sometimes: a single layer of asphalt can be roofed over only if an inspection finds it suitable. Otherwise it comes off first.
How do I compare the cost of metal and asphalt?
Get both prices in writing and compare them over the years you'll own the home, including the next asphalt replacement. For an Interlock® roof, book a free visit or call (206) 589-8423.
Sources
- National Association of Home Builders / Bank of America Home Equity: Study of Life Expectancy of Home Components (February 2007)
- Guardian Lifetime Limited Material Warranty (full document, PDF)
- Oregon State University Extension Service: How to control roof moss and prevent long-term damage
- ICC-ES Evaluation Report ESR-1790, Interlock Roofing, reissued September 2025 (PDF)
- Interlock Roofing: aluminum shingles, technical specifications
Product specifications are the manufacturer's (Interlock Roofing). Install counts are from our own job book. Reviewed by Scott Plumptree, October 7, 2026.
Get a written price to compare.
A written price after your roof consultation, at your home or on Zoom. Interlock Metal Roofing (PNW) Inc. · 5608 17th Ave NW, Suite 1574, Seattle, WA 98107-5232 · 2219 Rimland Dr, Suite 301, Bellingham, WA 98226-8660 · 26910 92nd Ave NW, Suite 425, Stanwood, WA 98292
