What Are the Disadvantages of Aluminum Roofing in Oregon? An Honest List

What is the biggest disadvantage of aluminum roofing in Oregon?

Cost. An aluminum roof costs more upfront than asphalt shingles and, in most bids, more than painted steel. There is no way to soften that on a Willamette Valley quote sheet, and any contractor who tells you otherwise is selling. If your plan is to own the house for five years and move, the math on aluminum is hard to make work. The number changes when you look at what asphalt actually does west of the Cascades. Multnomah and Clackamas counties average around 58 inches of rain a year, and Benton County around 60, with north-facing slopes staying damp from October through May. Moss roots between the granules, lifts the tabs, and the homeowner pays for a wash-and-treat cycle every few seasons until the roof gives out well short of its rated life. Many Portland homes are already on their second asphalt layer for exactly this reason. An interlocked aluminum roof gives moss nothing to root into and carries a 50+ year service life with a lifetime material warranty to the original owner. Priced against two or three asphalt roofs plus the moss treatments in between, the gap narrows considerably. It is still more money on the day you write the check. It is usually the last roof check you write for that house.

Does aluminum roofing dent in Oregon hail?

Aluminum is a soft metal compared with steel, so a hard enough strike will leave a cosmetic mark. The relevant question is where in Oregon you live. West of the Cascades, damaging hail is uncommon; the Portland metro, Salem, Eugene, and the coast get soft spring pea hail that does nothing to a roof. East of the crest it is a different climate. Wasco County sees 18 inches of rain but 48 freeze-thaw days, and Hood River County records 76 inches of snow and 55 freeze-thaw days, and both sides of the Gorge get real convective hail some summers. When a stone does hit aluminum, the panel flexes and takes the impact rather than fracturing the way an asphalt mat or a concrete tile does. The dent is cosmetic. The roof stays watertight. Interlock aluminum carries UL 2218 Class 4 impact rating, the highest class in the test, and the material warranty covers hail up to 1.5-inch stones. Ask your carrier whether a Class 4 roof earns an impact-resistant discount; some Oregon insurers offer one and some do not. A textured profile matters here. A cedar shingle, shake, or slate pattern has enough surface relief that a small dent disappears into the texture. A wide, flat standing seam pan in a dark color on a Gorge-facing slope will show a strike more plainly. If you are in The Dalles or Hood River and plan to look at the roof from the street for forty years, that is worth weighing before you pick a profile.

What about falling branches on Portland roofs?

In Portland neighborhoods the realistic dent risk is not weather. It is the Douglas fir in the back yard. Laurelhurst, Mt. Tabor, Sellwood, the West Hills, Lake Oswego, and most of the older tree-canopy streets in the metro have 80- to 150-foot firs that shed limbs in the winter wind. Multnomah County gusts are documented to 72 mph and Washington County to 75 mph, and the ice storms that come through every few years bring limbs down by the truckload. A limb the size of your forearm dropped from 60 feet will mark an aluminum roof. It will also punch through an asphalt roof, crack a concrete tile, or split a cedar shake, and those failures leak. Aluminum dents and keeps shedding water. There are 374 of these roofs on record in Portland since 1998, most of them under exactly this kind of tree cover. The honest disadvantage is that the dent is permanent unless you replace the panel. With an interlocking shingle system, replacement is a single panel unhooked and swapped, not a section tear-out, which is one reason the shingle and shake profiles make sense under heavy tree cover. If a large limb is hanging over the roof, have an arborist take it down before the roof goes on. That advice applies to any roofing material in Portland.

Does aluminum roofing oil-can, and does it matter in Oregon?

Oil-canning is the visible waviness that shows up on wide, flat metal panels when light rakes across them. It is a fact of sheet metal, aluminum included, and it does not affect performance or the warranty. It is purely a matter of how the roof looks at 4 p.m. on a low-sun January afternoon, which in the Willamette Valley is most afternoons. It shows most on standing seam with wide pans, on long unbroken runs like a ranch-style roof in Beaverton or Hillsboro, and in dark glossy colors. It also gets worse when a roof deck is uneven, which is common on older Portland Craftsman bungalows and foursquares whose sheathing has moved over a century, and on any house where a second asphalt layer was left in place under the metal. Fastening tension, thermal movement, and deck flatness all feed into it. The cure is mostly choice of profile. Interlock cedar shingle, shake, slate, and tile profiles are stamped with texture and installed as individual interlocking panels, so there is no wide flat plane to ripple. If you want standing seam for a modern house in Bend or a farmhouse in Silverton, ask for a narrower pan, a striated or pencil-ribbed panel, a matte finish, and a full tear-off to a flat deck. Those four things eliminate most of what people complain about.

Why does installer skill matter more for aluminum than asphalt in Oregon?

This is the disadvantage that does not show up on the material spec. An asphalt roof will survive a mediocre crew for a decade. An aluminum interlocking or standing seam roof will not forgive sloppy flashing, a skipped ice-and-water course, or fasteners in the wrong place, and the failures show up in the first winter when 50 to 80 inches of rain arrive over six months. Every good thing said about aluminum in this article assumes it was put on by someone who has done it before. Oregon adds two complications. First, the second asphalt layer many valley homes carry needs to come off. Oregon Residential Specialty Code limits roof layers, and a proper metal job means a full tear-off to bare deck, rotten sheathing replaced, and a synthetic underlayment over the whole thing before the first panel goes on. That is more labor and more disposal than a shingle-over, and it is where a cheap bid usually cuts the corner. Second, the coast and the Gorge push a roof harder than most of the country: Tillamook County gets 81 inches of rain and gusts to 85 mph, Clatsop County gusts to 91 mph. The interlock system is documented in ICC-ES ESR-1790 to 177.5 psf uplift, but only when every panel is hooked and every edge is fastened as designed. Check the Oregon CCB license, ask how many aluminum roofs the crew has installed, and ask to see one that has been through a few winters. Rain noise, incidentally, is not a real concern on a properly installed aluminum roof: over a solid plywood deck with underlayment it sounds like any other roof, and the homes on record in Salem, Eugene, and Corvallis are not the tin sheds people picture. Rust is not a concern either. Aluminum contains no iron, so a house in Newport or Cannon Beach in salt air has no steel-roof corrosion clock running. The disadvantages of aluminum in Oregon are real but short: price, cosmetic dents, oil-canning on flat pans, and the installer. The rest is asphalt's problem.

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