Knowledge Base · Moss & Rain
How Often Should You Replace a Roof in Western Washington?
Asphalt shingle roofs in western Washington typically need replacement at 15 to 25 years, and the wet-side climate pushes most of them toward the short end of that band. Cedar varies more widely. An Interlock aluminum system is engineered as a lifetime roof, warranted for life to the original owner.
Technically reviewed by Scott Plumptree, Director of Marketing, Interlock Metal Roofing · Updated 2026-08-15
At a glance
- Asphalt in western Washington generally runs 15 to 25 years, with shaded and wooded properties landing nearer 15.
- Sustained moisture, not storm damage, is what usually ends an asphalt roof's life on this side of the Cascades.
- Replacement cycles compound: a homeowner staying 40 years may buy two or three asphalt roofs in that time.
- Interlock aluminum is warranted lifetime to the original owner, transferable once, with the second owner covered to 50 years from substantial completion.
- Interlock has completed 3,223 Washington installations since 1997, with more than 750 approved Washington reviews and more than 200 documented Washington project photos.
Why does asphalt reach the short end of its range here?
An asphalt shingle ages by losing the volatile oils that keep its asphalt layer flexible, and by losing the mineral granules that shield it from ultraviolet light. Both processes are accelerated by a surface that stays wet. Water sitting in the granule texture, moss anchored in the keyways and debris trapped along the butt edges all keep the covering damp for far longer than the manufacturer's test conditions assume. The wet season in western Washington runs roughly October into June. That length of exposure, rather than any single storm, is what wears the covering down. A roof that would comfortably reach the upper end of its rating in a dry climate with long summers gets far fewer of those drying periods here. The practical result is a spread rather than a single number. A well-ventilated roof on an open lot with good sun exposure can reach the upper end of the range. A low-pitch north slope under a stand of firs frequently does not.
What actually determines when a roof has to come off?
Age is the starting question, not the answer. What matters is the condition of the covering and the deck beneath it. Granule loss showing as dark patches, shingles curling or cupping at the edges, cracked or brittle tabs, and repeated small leaks in different places are the signals that a roof has stopped being repairable and become a replacement. The attic tells you at least as much as the roof surface. Stained sheathing, damp insulation, rusted nail points showing condensation, or any softness underfoot on the decking means moisture has been getting in or has been trapped from below. That changes the scope of the work, because decking replacement is not a shingle question. Flashing is the third factor and often the deciding one. Chimney, sidewall, valley and penetration flashings fail before the field of the roof does in many cases. A roof that is otherwise sound but leaking at every penetration is a different conversation than a roof that is worn out across its whole area.
How do replacement cycles add up over time in a home?
The relevant arithmetic is not the life of one roof, it is the number of roofs a house needs across the time somebody owns it. On a 15 to 25 year asphalt cycle, a homeowner who buys in their thirties and stays put is looking at a second roof and quite possibly a third. Each of those is a full tear-off, disposal, and reinstallation, along with the disruption that comes with it. Each cycle also carries the cumulative risk of what is found underneath. Deck damage discovered on the second replacement is deck damage that has been developing during the life of the first roof. Interim maintenance sits on top of that, including moss treatment, gutter work and flashing repairs across the years between replacements. That is the frame a lifetime system is meant to change. Rather than a shorter interval repeated, the objective is one installation that is intended to remain on the building.
What does a lifetime aluminum system mean in practice?
Interlock's system uses 3105-H24 or 3003-H24 aluminum to ASTM B209 with roughly 95 percent recycled content. Aluminum cannot rust, which is the relevant property in a marine and high-rainfall environment, and the panel is finished with an AAMA 2605 70 percent PVDF Alunar coating that carries a 30-year coating warranty on the finish itself. The engineering is documented rather than described. The system holds ICC-ES ESR-1790 for wind uplift to 177.5 psf, reissued in September 2025, and is tested to UL 2218 Class 4, the highest impact classification in that standard. A Class A fire rating is available depending on the assembly specified, so it should always be discussed as assembly-dependent rather than assumed. The warranty is written to match that intent. The Guardian Lifetime Limited Material Warranty covers the original owner for life. It transfers once, and the second owner is covered to 50 years from substantial completion. Registration is required within 60 days of completion.
How do you tell where your current roof stands?
Start with the installation date and the material. If the paperwork is gone, a home inspection report from the purchase often records the roof's condition and estimated age. From there, look at the roof from the ground with binoculars rather than climbing on it: check for uneven color from granule loss, lifted or missing tabs, moss mats in the keyways, and any sagging line along the ridge or between rafters. Then check the attic on a dry day and again during a heavy rain if you can. Daylight through the sheathing, water staining, damp insulation and a musty smell are all worth acting on. Ventilation problems show up here first and are worth correcting whether or not you replace the roof. When Interlock estimates a Washington roof we assess the existing covering, the decking condition and the attic ventilation together, because a new roof over an under-ventilated attic inherits the same moisture problem. Interlock Metal Roofing is Washington's authorized installer of the Interlock Lifetime Roofing System, Washington licence #INTERMR75406.
Common questions
How long does an asphalt roof last in the Seattle area?
Asphalt shingle roofs in the Seattle area typically last 15 to 25 years, with shaded, wooded or low-pitch properties landing nearer the lower figure. The limiting factor is sustained moisture rather than storm damage, because a surface that stays damp for most of the year ages faster than its rating assumes.
Does a metal roof need replacing on a schedule?
An Interlock aluminum roof is engineered as a lifetime system rather than a scheduled replacement. Aluminum does not rust, the AAMA 2605 PVDF coating carries a 30-year finish warranty, and the material warranty runs lifetime to the original owner, transferring once with the second owner covered to 50 years from substantial completion.
Should I replace my roof before it starts leaking?
Usually yes, if the covering shows widespread granule loss, curling or repeated failures in different locations. Waiting for a leak means water has already reached the decking, which turns a covering replacement into a decking repair as well. Isolated flashing failures on an otherwise sound roof can often be repaired instead.
Can a new roof go over the existing shingles?
Interlock installs over a properly prepared roof deck and evaluates the existing covering, decking condition and attic ventilation before specifying anything. Layering a new roof over a deteriorated deck or an under-ventilated attic carries the underlying problem forward, so those conditions are assessed at the estimate rather than after work starts.
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