Aluminum Roof Repair in Oregon: What Actually Needs Fixing After 20 Winters

What actually wears out on an aluminum roof after twenty Oregon winters?

Almost never the aluminum. A Multnomah or Clackamas county roof takes roughly 58 inches of rain and 36 freeze-thaw days in an average year, and that water and movement go looking for the weakest detail on the roof. On an aluminum roof, the panels are the strongest detail. The 3105-H24 and 3003-H24 alloy contains no iron, so twenty winters of standing water and wet fir needles produce no rust, and the Alunar 70 percent PVDF finish is warranted for 30 years. What has aged is everything that meets the aluminum: sealant at a chimney counterflashing, the rubber boot on a plumbing vent, the caulk bead where a dormer sidewall meets the roof, and the underlayment under a valley that has spent every October through May under Douglas fir debris. Portland alone has 374 of these roofs on record since 1998, with another 48 in Oregon City going back to 1996. The pattern changes by region. In the Willamette Valley it is flashing and debris. On the coast, in Clatsop, Tillamook and Lincoln counties, it is salt attacking any steel component mixed into the assembly, such as a galvanized chimney cap, while the aluminum next to it is fine. In the Gorge, with Hood River seeing 76 inches of snow and 55 freeze-thaw days, it is ice working at the eave and the sealant at every penetration.

Why does flashing fail first on Portland bungalows and foursquares?

Portland's Craftsman bungalows and foursquares were built with brick chimneys, low-slope porch roofs, and shed or gable dormers, and each of those is a place where water has to change direction. A chimney on the north slope of a bungalow in Southeast Portland is wet for seven months of the year. The brick wicks moisture, the mortar joints holding the counterflashing open a little more each freeze-thaw cycle, and the sealant that was doing the real work when the roof went on hardens and pulls away from the masonry. A dormer is the same problem turned sideways. The step flashing up the sidewall is usually sound, but the point where the dormer cheek meets the main roof collects debris, and the kickout at the bottom of the wall, if the original roofer installed one, is where stains show up on the siding below. On many of these houses the aluminum went on over a second layer of asphalt, which raised the roof surface and reduced flashing height at these walls. Twenty years later that height is the difference between a dry wall and a wet one. The repair is not exotic. Old sealant is cut out, counterflashing is reset into the mortar joint, step flashing is re-lapped where it has slipped, and a kickout is added if it was never there. On an interlocking aluminum roof the surrounding panels can be released for proper access and then relocked, which is what makes a lasting flashing repair possible instead of a caulk-over. None of this touches the panels themselves.

Do Douglas fir needles and falling limbs damage an aluminum roof?

Needles do not damage aluminum, but they damage what is under it if left alone. A valley on a house under mature Douglas fir in Lake Oswego, West Linn, or the foothills above Molalla fills with needles every fall. The pile holds water, the water finds the underlayment through any seam along the valley, and the decking below softens over years. Benton and Lane counties, at 56 to 60 inches of rain, see this on almost any wooded lot. Moss follows the same logic. West of the Cascades, moss is the roof-killer, and it needs somewhere to root. Interlocked aluminum gives it nothing to grip, so a clean aluminum roof stays clean. A roof with a season of debris in the valleys gives moss a bed, and once established it holds moisture against the flashing details above. Clearing valleys and eaves each fall is the most effective repair-prevention job on an Oregon aluminum roof, and it can usually be done from a ladder. Limbs are different. A fir limb coming down in a 70 mph windstorm will dent an aluminum panel, and the dent is visible. Aluminum is softer than steel, and we do not pretend otherwise. What the dent is not is a leak. The panel is still locked on four sides, the finish is intact, and no iron is exposed to corrode. Most dents are left alone. A limb heavy enough to puncture a panel, which happens in the Gorge and on the coast, calls for replacing that one panel.

Is an old exposed-fastener steel roof harder to repair than interlocking aluminum?

Yes, and the difference is mostly the screws. Many Willamette Valley farmhouses, shops in Linn and Polk counties, and cabins on the east side went up with through-fastened steel panels: thousands of screws driven through the panel face, each sealed by a rubber washer. Those washers are the wear item. After twenty summers of sun and 37 to 40 freeze-thaw cycles a year, the rubber hardens, the panel expands and contracts around the screw, and the hole opens up. The standard repair is backing out every screw and replacing it with a larger fastener and new washer, hoping the panel has not corroded around the hole. On the coast that hope is often disappointed. A through-fastened steel roof in Tillamook County, under 81 inches of rain and salt-laden gusts to 85 mph, shows rust bloom at the fastener holes and cut edges well before twenty years. Many steel finish warranties exclude oceanfront exposure for this reason. At that point the repair conversation has become a replacement conversation, and it is fair to say so rather than sell another round of screws. Interlocking aluminum has none of this to service. The fasteners are concealed under the locked edge of the panel above, so they never see rain, sun, or salt, and the panel is held on four sides rather than pinned through its face. ICC-ES ESR-1790 documents that lock at 177.5 psf uplift, which is why a roof taking Gorge wind at The Dalles does not develop loose panels for a crew to chase.

When does a single panel swap beat replacing a section, and who should do it in Oregon?

A single panel swap is the right repair when the damage is local and the rest of the roof is sound, which on aluminum is almost always the case. A punctured panel from a limb, a panel creased when a satellite installer stepped in the wrong place, or a panel scratched through the finish by dragged gutter guards can each be released from its neighbors, lifted out, and replaced with a matching panel locked into the same four edges. The surrounding panels are not disturbed, the underlayment is not cut, and the roof is watertight the same afternoon. A section replacement is warranted only when several adjacent panels are damaged together, typically a fallen tree rather than a limb, or when the damage reaches the decking. It is also the answer when someone has previously face-screwed or caulked over a problem and the panels cannot be cleanly relocked. Whoever does the work in Oregon should hold a current Construction Contractors Board license, and you can check it by number on the CCB website before anyone climbs a ladder. Interlock Metal Roofing (PNW) Inc. works under Oregon CCB #130826. Licensing matters more for repair than for a new roof because repair is where unlicensed handymen appear, and an interlocking aluminum roof repaired with roofing screws and a tube of caulk has been made worse, not better. A roof installed to last a lifetime deserves a repair done to the same standard.

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