Can You Replace a Slate Roof With Metal on an Older Oregon Home?

Can you replace a slate roof with metal in Portland or Salem?

Yes, and in Oregon it is often the only realistic option once the slate starts to go. Real slate never took hold here the way it did in the Northeast. The roofs that exist sit on a handful of Victorians and larger foursquares in Portland's older neighborhoods and on a few institutional and older residential buildings in Salem, most of them roofed before 1930. That small population means there was never a trade to support it. Copper craftsmen are scarce in Oregon and priced accordingly, and slaters are scarcer still. Homeowners who call around for a slate repair usually end up with a general roofer walking the roof in boots, which cracks more slate than it fixes. The slate itself is also tired. Multnomah and Clackamas counties average about 36 freeze-thaw days a year and Marion County about 39, and a century of water soaking into the stone and freezing in the laminations causes it to spall and delaminate along the edges. Once that starts, individual pieces slip, the nail holes enlarge, and the roof leaks in the same rain that soaks the rest of the valley from October to May. Replacing the whole roof with an aluminum slate profile keeps the appearance while ending the search for a slater who does not exist.

Does taking the slate off help a house framed in the early 1900s?

It helps more than most owners expect. Natural slate weighs somewhere between 8 and 15 pounds per square foot depending on thickness, and the Portland houses that carry it were framed with full-dimension lumber that has been holding that load for a hundred years. Aluminum slate shingles weigh about half a pound per square foot. On a typical 30-square roof that is many thousands of pounds coming off rafters, ridge boards, and bearing walls that have often already sagged a little at the ridge or bowed at the eaves. We see the consequences of the load on tear-off in Irvington, Laurelhurst, and the older streets of Salem: rafters that have deflected between purlins, sheathing boards that have cupped, and skip-sheathing gaps wide enough to lose a foot through. None of that is an argument for adding more weight. Because aluminum takes the load off rather than adding to it, the framing question usually becomes one of repair rather than reinforcement. A structural review is still worth doing on any house of that age, and your installer should be able to show you the deck and framing condition with photos before the new roof goes on.

Do you need historic-district approval to change a slate roof in Oregon?

Possibly, and you should find out before you sign a contract. Several Portland neighborhoods and parts of Salem sit inside historic districts or carry individual landmark designations, and exterior changes on those properties can require design review. Rules vary by city and by district, so the practical step is to check with your local historic landmarks commission or the city's historic review staff and ask whether roofing material is a reviewed item on your property. Some jurisdictions only care about visible slopes from the street; others want the whole roof to match. This is where the profile matters. An aluminum slate shingle is stamped from molds taken off real slate, laid in the same staggered coursing, and finished in slate grays, blacks, and greens with a 70 percent PVDF coating. From the sidewalk it reads as slate, which is the standard most review boards apply. Bring the manufacturer's profile sheet and a color sample to the review meeting; boards respond to physical samples better than to product photos. Interlock Metal Roofing (PNW) has 374 roofs on record in Portland since 1998 and 87 in Salem since 1999, and a share of those sit on older homes where the slate look was the reason the owner chose the profile.

What happens to the old slate, and what does the tear-off look like?

Slate tear-off is slower and heavier than stripping asphalt. The stone comes off in courses, gets lowered rather than thrown, and fills a dumpster fast because of the weight. Sound pieces have value. There is a salvage market for reclaimed slate, mostly outside Oregon where slate roofs are common and repair stock is in demand, and a roofing crew that knows the material will palletize the intact pieces rather than crush them. Broken slate is inert stone and goes to a landfill or a clean-fill site. Ask your contractor up front who owns the salvage and whether it offsets any of the disposal cost. Under the slate is usually plank or skip sheathing, often with a felt that has gone to dust. The deck gets inspected board by board, rot around chimneys and valleys is cut out and replaced, and gaps in skip sheathing are filled or the deck is overlaid with new plywood or OSB so the aluminum has a continuous nailing surface. Then a high-temperature underlayment goes down, followed by the new flashings and the shingles. Confirm your installer holds a current Oregon CCB license and carries the workers' compensation coverage that a job with this much lifting requires.

Will aluminum slate hold up against Oregon moss and weather?

Better than the slate did. West of the Cascades the roof-killer is moss, not storms, and old slate roofs grow it thickly along the laps where the overlapping edges hold water and shade. Moss on slate wicks moisture back under the courses and holds it against the nails, which is how so many Portland slate roofs end up with rusted-out fasteners and slipped pieces. Interlocked aluminum shingles have tight laps and a smooth PVDF finish that give moss nothing to root into, and a north slope that used to need a wash-and-treat cycle every few seasons generally stops needing one. The oldest Oregon roof in our photo gallery is a black aluminum slate installed in Eugene in 2017, in Lane County's 56 inches of annual rain and 34 freeze-thaw days, and it looks the way it did the day it was finished. Aluminum contains no iron and cannot rust, so the freeze-thaw and standing-water cycle that spalled the old slate does not touch it. The shingles are UL 2218 Class 4 impact rated and the four-way interlock is documented in ICC-ES ESR-1790 to 177.5 psf uplift, which is more than any Willamette Valley windstorm has asked of it. Be honest with yourself about the trade-off: you are giving up genuine stone, and aluminum can dent under a dropped ladder or a heavy tree limb. What you get is a roof that weighs almost nothing, keeps the look the house was built with, and carries a lifetime material warranty, so the slater you could never find is no longer someone you need.

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