Free roof inspection with deck photos before we talk money - GAF and Owens Corning certified installation
Before
After
Before
After
Before
AfterCertainTeed Underlayment & Deck Repair: The Los Angeles Owner’s Guide
If you’re searching for CertainTeed underlayment and deck repair in Los Angeles, here’s the straight answer: we stock CertainTeed-compatible underlayment and plywood decking on our trucks, and most repairs run between $450 and $1,800 installed depending on how much decking has rotted and how many squares of underlayment need replacing. Same-week scheduling is typical for us, not same-day. The way most Los Angeles homeowners discover this problem: a leak shows up on the ceiling after a heavy rain, or a roofer doing a shingle replacement lifts the old felt and finds the decking underneath has turned to sponge.
Underlayment is the waterproof layer between your roof deck and your shingles. Decking (also called sheathing) is the plywood or OSB that everything sits on. When either fails, water gets into places it shouldn’t, and Southern California’s heat and occasional pounding rainstorms accelerate the damage quietly for months before you see it inside.
Which CertainTeed Models This Applies To
This page covers repairs under any CertainTeed shingle line installed in the Los Angeles market, including Landmark, Landmark Pro, Presidential Shake, XT 25, and the Grand Manor and Carriage House luxury lines. The underlayment and decking underneath don’t care which shingle is on top. What matters is what was installed originally and what condition it’s in now.
Here’s the compatibility detail most homeowners never hear: CertainTeed warranties for Landmark and above require a specific underlayment class, typically a synthetic like CertainTeed’s own DiamondDeck or RoofRunner, or a #30 felt minimum. If your original installer used 15-lb felt or builder-grade paper, the shingle warranty was compromised from day one. When we do a repair in Los Angeles, we check what’s actually on the deck and match the replacement to what the shingle line calls for, not just what’s cheapest at the supply house. L.A. County code also requires a minimum of one layer of ASTM D226 Type II felt or an approved synthetic, which is a lower bar than CertainTeed’s own spec, so don’t assume code-compliant means warranty-compliant.
We’re an independent roofing contractor that installs and repairs CertainTeed products. We’re not affiliated with CertainTeed, and we don’t pretend to be. We do stock their underlayment products alongside equivalent materials from GAF and Owens Corning, and we’ll tell you honestly when an aftermarket synthetic performs as well as the OEM product for less money.
Signs Your CertainTeed Underlayment & Deck Repair Is Failing
- Water stains on ceilings or walls after rain. This is the most common first sign. By the time water is visible inside your home, it has already passed through the shingles, the underlayment, and the decking. The stain you see is the last stop on a longer trip.
- Granules collecting in gutters or at downspout bases. CertainTeed shingles shed granules as they age, but a sudden surge means the shingle itself is degrading and likely exposing underlayment beneath. If you’re seeing bare fiberglass showing through, water is not far behind.
- Soft spots when walking the roof or visible sagging between rafters. Spongy decking means rot has already set in. Los Angeles humidity near the coast accelerates this, and homes within five miles of the Pacific get more of it than homeowners expect.
- Daylight visible through attic boards or water trails on rafters. If you can see light through the deck from inside the attic, the structural layer has gaps that underlayment alone was never designed to bridge. This is direct evidence of deck failure.
- Lifted, curling, or missing shingles exposing the layer underneath. CertainTeed’s fiberglass asphalt shingles seal with heat activation, but after years of Los Angeles sun and the occasional Santa Ana wind event, sealant strips fail and shingles lift. The underlayment is then doing the only waterproofing work, and it wasn’t rated for that job alone.
Replacement Cost & What’s Included
In Los Angeles, expect these installed ranges for deck and underlayment repair:
- Underlayment replacement only (single layer, tear-off and reinstall): $180 to $350 per 100 square feet (one square)
- Deck repair with plywood replacement for rotted sections: $2.50 to $5.00 per square foot replaced, including materials, fasteners, and disposal
- Full deck replacement (complete re-sheathing): $4,500 to $9,000 for a typical 1,500 to 2,000 sq ft Los Angeles roof
- Combined underlayment and partial deck repair (most common job): $450 to $1,800, with the variance coming from how much deck is rotted once we open it up
The honest truth about deck repair pricing: no roofer can quote a final number until the old underlayment is peeled back and we see what’s underneath. What we can guarantee, and what sets us apart, is this: you get a written price before any work starts, and that written estimate includes our contingency assumptions for deck exposure. If we find more rot, we show you photos, we show you measurements, and we agree on the additional figure before we cut another sheet of plywood. No surprise invoice. Our 365-Day Done Right Promise covers every repair, and if something fails within a year, we return and fix it without a second invoice.
DIY or Call Us?
You can safely do the inspection work: get into the attic with a flashlight on a sunny day and look for light gaps and water trails. Walk the roof only if you’re comfortable with heights and have a stable ladder, and check for soft springy sections. Those observations help you understand what a roofer will tell you.
What we don’t recommend is partial DIY deck replacement. Rotted decking is structural, not cosmetic. Cutting out a section while actively standing above the area you’re cutting changes the load distribution in ways that surprise even experienced contractors. If you replace decking and don’t seal the joints properly, you’ve installed a leak. If you misalign the new underlayment, the CertainTeed warranty paperwork is void and nobody will catch it until water is inside. For what a proper repair costs in Los Angeles, the risk-reward on this one points one direction. Call (743) 200-8347 and we’ll give you a written estimate, not a pitch.
FAQs
CertainTeed’s synthetic underlayments, like DiamondDeck, are rated to perform for the life of the shingle, but real-world lifespan in Southern California runs 15 to 25 years depending on sun exposure, attic ventilation, and whether the roof was ever walked on after installation. Concrete or tile roofs in Los Angeles often outlive their underlayment, which is a common repair scenario we handle. Call (743) 200-8347 for a free estimate and we’ll tell you exactly what’s under your shingles.
Yes, in some cases. Small tears or gaps caused by replaced vent boots or satellite mounts can be patched with the correct material and proper overlap, and this runs under $200 in most Los Angeles homes. But if the underlayment is brittle, cracked, or showing signs of age across a whole slope, patching it is throwing good money after bad, and we’ll tell you that plainly. Estimates are free, so call (743) 200-8347 and hear it from us directly.
Most repairs take one to two working days. Day one is tear-off, deck replacement, and underlayment install. Day two is shingle reinstallation and cleanup. If we’re replacing the entire roof, plan for two to four days depending on size and weather. Los Angeles rain is rare enough that you’ll get a clear window, and we schedule accordingly.
Yes. Our service trucks in Los Angeles typically carry CertainTeed DiamondDeck and RoofRunner in multiple widths, plus #30 felt for budget repairs and matchable plywood decking. We also carry GAF and Owens Corning equivalents when a job calls for a specific product the homeowner already has. Most repairs don’t even require a supply-house run.
Grant Whitlock will tell you the thing he’s learned across almost two decades of Los Angeles roof work: underlayment and decking fail quietly, and homeowners catch it late because they’re never looking for it. His crew does the looking for you. A roof that’s doing its job is one you never think about. Let’s keep it that way.
Call (743) 200-8347 to schedule your free estimate. Every visit starts with a name and a photo sent before our background-checked, photo-badged technician knocks on the door. Written price first, written guarantee always, and a real person answers the phone 24/7.
Written by Grant Whitlock, Owner, Mercer Roofing at Mercer Roofing, serving Los Angeles and nearby areas.