IKO Underlayment & Deck Repair in Seattle, WA

IKO Underlayment & Deck Repair: The Seattle Owner’s Guide

IKO underlayment and deck repair in Seattle typically runs $1,800-$4,200 installed, depending on how much decking has rotted through and whether we’re working around skylights or steep pitches. We stock IKO ArmourGard and StormTite synthetic underlayment on every truck, plus CDX and OSB decking in common thicknesses, so most jobs start same-day. Most homeowners first notice the problem during a hard rain: water stains spreading across the ceiling, shingles that look fine from the street but are riding on soaked, crumbling wood underneath.

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Which IKO Models This Applies To

This applies to every IKO shingle system installed in the Pacific Northwest, from the legacy Cambridge AR and Marathon Plus lines still common in Magnolia and Wedgwood, to newer Dynasty and Cambridge Cool Colors roofs going up in Ballard and Columbia City. The underlayment beneath doesn’t care which shingle brand is on top, but IKO’s own synthetic underlayments, ArmourGard and StormTite, are engineered to their specific fastening patterns and exposure ratings. If you’re trying to identify what’s on your roof now, look for the IKO logo printed along the underlayment roll edge, usually visible at the rake or where a shingle has blown off. The stamp will show the product name, ASTM D226 or D4869 compliance, and sometimes a lot number.

We are an independent service provider, not affiliated with IKO. That said, we source IKO-branded underlayment through authorized distribution, and we also carry Grace Ice & Water Shield and Titanium UDL as quality alternatives when the job calls for it. The OEM-versus-aftermarket question usually comes down to warranty: if your IKO shingles are still under their limited warranty, mixing in non-IKO underlayment during a repair won’t void coverage, but using IKO-branded material keeps the documentation cleaner. For deck repair, there is no “IKO deck” - it’s standard CDX plywood or OSB, and we match thickness to what’s in place, typically 15/32″ or 19/32″ in Seattle’s older homes, 7/16″ OSB in post-1990 construction.

Signs Your IKO Underlayment & Deck Repair Is Failing

• Water stains on the ceiling that grow after every rain. The underlayment has torn or the fasteners have backed out, letting water run down the deck and pool in the insulation. In Seattle’s climate, this happens faster on north-facing slopes where moss holds moisture against the shingle edge and wicks it underneath.
• Soft spots when you walk the roof, or visible sagging from the ground. The OSB or plywood deck has delaminated or rotted through, usually at the eaves where gutters overflow or in valleys where two roof planes dump water. We’ve replaced entire 4×8 sheets in Leschi that were mush from the top down but looked fine from the attic because the stain hadn’t broken through yet.
• Shingles curling or blowing off in clusters. When the deck flexes, the nail pops; when the nail pops, the shingle loses its grip. IKO Cambridge shingles are heavier than some competitors, so a compromised deck shows the strain sooner, especially on 4:12 pitches common in Ravenna and Green Lake bungalows.
• Black mold spots in the attic, especially near the soffits. Failed underlayment lets humid exterior air into the roof assembly, and Seattle’s cool, wet springs keep that moisture from drying. The mold is a symptom; the underlayment gap is the disease.
• Ice dam damage after a freeze, even a mild one. ArmourGard is rated for ice dam protection, but if it was installed without proper overlap at the eaves or if the self-adhering strip failed, water backs up under the shingles and into the wall cavity. We see this every few winters when a cold snap hits after a warm, rainy December.

Replacement Cost & What’s Included

The range depends on three things: how much decking needs replacement, how steep the roof is (steep pitches in Queen Anne or West Seattle take longer and require more safety setup), and how many penetrations we’re working around - skylights, vent pipes, chimneys. Every estimate we write breaks out material, labor, and disposal separately. The number on the estimate is the number on the invoice. Our 90-Day Done Right Promise covers the workmanship: if a seam lifts or a fastener backs out, we come back and make it right, no paperwork, no arguing.

DIY or Call Us?

There is honest work a homeowner can do from inside the attic: tracing the water path, photographing the stain pattern, checking for daylight through the roof deck. That information helps us diagnose before we even set a ladder. But once you’re on the roof, the risks stack fast. Seattle’s composite shingles are slick with morning dew eight months of the year, and a rotted deck won’t hold a ladder foot or a roofing nail. Removing shingles to expose underlayment without tearing the surrounding field takes a flat bar and a feel for the fastener depth that comes from years of doing it.

We don’t recommend homeowners pull decking or handle synthetic underlayment installation themselves. The self-adhering membranes need proper temperature to bond, and in Seattle’s spring and fall, that window is narrower than most people realize. A good roof doesn’t ask for your attention. That’s the whole point. If you’re seeing stains or soft spots, call (866) 850-9676 and we’ll get a technician out with a camera, a ladder, and the material to fix it.

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