IKO Underlayment & Deck Repair Nationwide

IKO Underlayment & Deck Repair: The San Francisco Owner’s Guide

IKO underlayment and roof deck repair in San Francisco typically runs $450 – $1,850 installed, depending on how much decking has rotted and which IKO underlayment your roof system calls for. We stock IKO-compatible underlayment rolls and decking on our trucks, so most repairs are done in a single visit. The way owners usually find out this part has failed is water staining on a ceiling, curling shingles near a vent, or a roofer pointing it out during an inspection. Here’s what actually happens under those shingles and what it costs to fix it right.

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San Francisco’s marine air is the quiet killer here. Fog sits on roofs for hours in the Richmond and Sunset districts, keeping underlayment damp long after the shingles look dry. Once moisture works into the decking, the plywood starts to delaminate. Travis Oakley has pulled back shingles in the Sunset and found decking so soft a screwdriver sinks in like it’s butter. The shingles looked fine from the street. The underlayment had failed first, like it almost always does.

Which IKO Models This Applies To

IKO makes a few different underlayment products, and they’re not interchangeable. The two you’ll most likely find on San Francisco roofs are IKO’s felt underlayment (15 lb and 30 lb) and their synthetic lines like IKO Stormtite or IKO’s peel-and-stick products. Each has a different weight, thickness, and nail pattern. Using the wrong one under IKO shingles can void the manufacturer’s wind warranty, and that’s a compatibility gotcha most homeowners never hear until it’s too late.

Here’s how to tell what you have. If you kept the original roof paperwork, the underlayment spec is listed in the materials line item. If not, the felt number is sometimes printed on the exposed edge near a rake or eave. For synthetic, look for a woven-looking surface and a printed grid pattern for nail spacing. If you can’t read it, we’ll identify it during the estimate.

On the decking side, San Francisco homes built before the 1980s often have 1×6 tongue-and-groove pine rather than plywood. That matters because the repair approach is different – you can’t always patch one small section of old growth T&G without matching the board thickness. Newer homes usually get 1/2-inch or 5/8-inch CDX plywood, which is easier to spot-repair. We’ll tell you which you have and write the cost down before anything gets torn off.

One note on OEM versus aftermarket: IKO manufacturers underlayment, but they don’t make the plywood decking. So the underlayment is matched to IKO specs, and the decking is a structural material we source from local San Francisco lumber suppliers to meet code. No mystery there, and no markup on the difference. Brennan Roofing Co San Francisco is an independent service provider, not affiliated with IKO, but we install their underlayment to manufacturer spec every time, and we also stock GAF, Owens Corning, and CertainTeed parts for roofs that have mixed materials.

Signs Your IKO Underlayment & Deck Repair Is Failing

• Water staining or a soft spot on the ceiling – This is the classic sign that underlayment has worn through and water has reached the decking. By the time you see it inside, the decking has usually been wicking moisture for weeks or months, and the repair is no longer just a shingle swap.
• Curling or lifting shingles near roof penetrations – Vents, pipes, and skylights are where underlayment degrades first. The sealant dries out in San Francisco’s temperature swings, water gets under the shingle edge, and the underlayment holds it against the deck. Curling at the edges means the fastening surface is compromised.
• Granules in the gutter but no visible bare shingles – IKO shingles hold their granule layer reasonably well, so if you’re seeing heavy granule loss in the downspout, the shingle has been flexing. That flexing almost always comes from uneven or rotted decking underneath.
• A musty or damp smell in the attic after a fog spell – San Francisco fog doesn’t just sit on top of the roof; it gets pulled into the attic through soffit vents. If the underlayment is porous, the decking behind it stays damp and starts to smell. That’s a warning sign you can catch before a full structural failure.
• Visible gaps or sagging between roof rafters when viewed from the attic – If the decking is rotting from the underside, you’ll see discoloration, dark streaks, or actual sagging between rafters. This is the deck telling you it’s load-bearing days are numbered.

Replacement Cost & What’s Included

In San Francisco, a small deck repair with new IKO underlayment around a single penetration usually runs $450 to $750. A moderate repair covering a few sheets of decking and a full underlayment patch runs $800 to $1,250. A larger job, meaning ten or more sheets of decking replaced and full underlayment over a whole roof plane, lands between $1,500 and $1,850. The range comes down to three things: how much decking has to come out, how steep the roof is, and whether your roof has one layer or two of old shingles.

Every quote from Brennan Roofing includes the decking material, the IKO underlayment cut to spec, fasteners, disposal of the old material, and the labor to remove, repair, and reinstall shingles. The price goes on paper before any work starts, and it does not move at the door. We follow The Garrison Standard on this: written price, no change orders unless a hidden problem actually changes the scope, and we show you photos of what we found before we cover it back up.

All work is backed by our 365-Day Done Right Promise. If the repair fails within one year, we return and fix it at no charge, in writing. That’s not a vague warranty; it’s a specific one, and it covers the underlayment, the decking, and the shingle work above it.

DIY or Call Us?

You can safely inspect a few things from the ground or inside the attic: check for water stains on the ceiling, look for curled shingle edges from the sidewalk, and shine a flashlight at the decking from the attic access. What you shouldn’t do is pull up shingles and start cutting out decking. Once you break the shingle seal and expose the underlayment, you’ve created a new leak path you’re now responsible for closing before the next rain. And San Francisco rain doesn’t wait.

Where DIY really goes wrong is on steep roofs. A 6/12 pitch or steeper with damp underlayment is slicker than it looks, and a fall from even a single-story San Francisco roof sends people to the hospital every year. Trained roofers do this work on ropes and harnesses with proper anchors. If the decking has rot, you also need to check that the rafter underneath hasn’t lost its load capacity before you nail new plywood onto it. We do that as part of every deck repair, and we don’t charge extra for the inspection.

If you’ve got stairs, a hatch, and a healthy respect for gravity, keep your feet on the ground and call (831) 318-8819. We’ll come out, open up the roof, and give you a written price before any work starts.

FAQs

Call for a Free Estimate

If your IKO underlayment or deck is showing signs of failure, don’t wait for the next rain to confirm it. Call Brennan Roofing Co San Francisco at (831) 318-8819 and we’ll schedule a free estimate with a written price before any work starts. You’ll get a live person on the phone, a background-checked uniformed technician on your roof, and a one-year written guarantee on the repair. That’s The Garrison Standard, and it’s the same on every job we do.

Written by Travis Oakley, Owner, Brennan Roofing Co at Brennan Roofing Co San Francisco, serving San Francisco and nearby areas.