Boral Underlayment & Deck Repair Nationwide

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

Boral-compatible underlayment and deck repair in San Francisco typically runs $1,100 to $3,400 installed, depending on how much decking has failed under the surface. We stock Boral roof decking and underlayment on our trucks and can usually complete a standard repair in one day once the roof is opened. Most San Francisco homeowners discover the problem the same way: a soft spot near a scupper, a leak showing up on a ceiling after a heavy fog cycle, or a roofer from another company pointing at rotted decking during an unrelated repair.

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Here’s the reality: Boral makes good products, but no underlayment on Earth survives a deck that’s been quietly holding water for three seasons. In San Francisco, where marine air sits on flat roofs for months at a time, the underlayment is doing most of the waterproofing work. When the deck beneath it rots or sags, the underlayment fails right along with it. We see it most often on older Sunset District and Richmond District homes where flat roofs are the norm, not the exception.

If your Boral roof is leaking, bubbled, or soft underfoot, this page will tell you what you’re actually paying for, whether it’s worth patching, and how we handle it at Brennan Roofing Co San Francisco. We’re an independent service provider, not a Boral dealer or affiliate – which means we’ll tell you honestly if an aftermarket decking equivalent will do the job just as well as the OEM sheet.

Which Boral Models This Applies To

Boral’s roofing division has been through a few name changes over the years – Boral Roofing became part of the Westlake Royal Building Products umbrella, but San Francisco supply houses still call it Boral, and so do most roofers. The underlayment and deck repair work we do applies to Boral concrete and clay tile roof systems, plus the Boral Steel line on a smaller number of homes in the Bay Area.

The compatibility gotcha with Boral underlayment is this: Boral tile roofs in California are almost always installed over either two layers of ASTM D226 Type II asphalt-saturated felt (the classic 30-pound felt) or one layer of a high-temperature synthetic underlayment rated for tile. If your roof is older and still has cedar shakes underneath, that’s a different deck repair conversation entirely. The decking itself is typically 15/32-inch CDX plywood or 1×6 tongue-and-groove boards on older San Francisco homes, and it fails at the same rate regardless of what’s on top of it.

For OEM versus aftermarket: Boral’s branded underlayment is manufactured to spec and works well, but we regularly install GAF Deck-Armor, Owens Corning Deck Defense, and CertainTeed RoofRunner as quality equivalents. The decking is plain construction-grade material – there’s no such thing as “Boral plywood.” We’ll match what’s already on your roof, write the exact product name on your estimate, and explain why we chose it before any work starts. That’s the Garrison Standard, and it’s the same on every job we do in San Francisco.

Signs Your Boral Underlayment & Deck Repair Is Failing

• Water stains spreading across the ceiling below the roof. This usually means the underlayment has lost its bond or torn at a seam, and water is traveling between the deck boards before it finds a gap. In San Francisco, we see this worsen after the first real rain of the season, when the deck is already saturated from fog condensation.
• A soft or springy spot when someone walks the roof. That’s rotted decking, plain and simple. Underlayment cannot hold water out if the deck sags enough to create ponding, and in San Francisco’s flat-roof neighborhoods like the Outer Sunset, ponding is a year-round condition.
• Visible underlayment that looks brittle, cracked, or sun-baked near roof edges. If you can see felt or synthetic underlayment peeling at the drip edge, it has already exceeded its useful life. UV breaks down even high-quality underlayment fast once it’s exposed.
• Granules or fine debris collecting in gutters and downspouts. This usually comes from the tile itself, but on Boral systems, it often signals that the underlayment beneath has degraded and is allowing tile movement. The tiles grind against each other, and the granules wash down.
• A musty smell in the attic or upper floor after foggy mornings. San Francisco fog is the silent deck killer. It condenses on the underside of the roof deck, soaks the wood, and rots it from above. By the time you smell it, the deck has usually been wet for months.

Replacement Cost & What’s Included

Boral underlayment and deck repair in San Francisco runs $1,100 to $3,400 installed for a typical repair area of 100 to 400 square feet. Here’s the line-item breakdown we give every homeowner before any work starts:

The range comes down to two things: how much decking has actually failed once we open the roof, and whether your San Francisco home is in a flat-roof zone that requires two layers of underlayment per local code. We write the exact price on paper before any work begins, and that number does not move at the door. Every repair carries the 365-Day Done Right Promise: if it fails within one year, we come back and fix it at no charge, in writing. No change orders, no surprise line items.

DIY or Call Us?

A homeowner can safely check a few things from the ground or from a ladder: cracked or missing tiles near the roof edge, underlayment visible at the drip edge, water stains on the ceiling. Those observations help you tell us what you’re seeing. What you shouldn’t do is walk a tile roof to inspect the deck yourself – Boral tile is slippery when damp, which in San Francisco is most mornings, and a cracked tile underfoot on a steep Victorian pitch is a fast way to take a serious fall. We’re saying this from experience, not liability paperwork.

The underlayment itself is not a repair you can patch from above. It sits under the tile, and any repair means pulling tile, cutting out the failed section, inspecting the deck, and reinstalling everything in the right order. Do it wrong and you’ve just hidden a leak under a fresh layer of tile. If you’re in the Sunset, Richmond, or anywhere from Alamo Square to Noe Valley, call us at (831) 318-8819. We’ll inspect it, tell you what needs replacing now and what can wait, and give you a written price before any work starts.

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