Aerial view of a finished concrete tile roof by GAX Roofing
Homeowner Guide

Understand
Your Roof

The part you see from the street is not the part that keeps the water out. Here is how a roof is actually built, what wears out first, and how we decide between a repair, a lift and relay and a replacement.

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A Roof Is a System,
Not a Surface

Shingles and tile are the armor. Under them is the waterproof layer, under that is the wood deck everything is fastened to, and at every edge, wall and pipe there is metal flashing. When a roof leaks, the cause is almost always in one of those hidden layers, not the part you can see from the driveway.

These two drawings show the layers from the framing up. The numbers match the list under each one.

Asphalt Shingle Roof

An exploded drawing of a shingle roof from the rafters up: deck, drip edge, ice and water barrier at the eaves, underlayment, shingles and the ridge vent and cap.
  1. Rafters or trusses. The framing the roof sits on.
  2. Roof deck. Plywood or OSB sheathing. Everything else is fastened to it.
  3. Drip edge. Metal along the roof edges. Its little lip flicks water away from the fascia board instead of letting it soak in. At the eaves it goes on first and the waterproof layers lap over it; along the rakes (the sloped side edges) it goes on over the underlayment.
  4. Ice and water barrier. A self-sealing membrane in the spots that take the most water: the eaves, the valleys and around vents, chimneys and skylights.
  5. Underlayment. The synthetic layer across the rest of the deck.
  6. Starter strip and shingles. The layer you see. Shingles shed water and take the sun so the layers under them don't have to.
  7. Ridge vent and cap. Lets hot attic air out at the peak.
Illustration of a typical assembly with the layers pulled apart so you can see each one, not a drawing of a specific roof. The exact products and layers on your roof are named in your contract.

Concrete Tile Roof

An exploded drawing of a tile roof from the rafters up: deck, self-adhered underlayment, battens, concrete tile and ridge tile.
  1. Rafters or trusses. The framing.
  2. Roof deck. The wood sheathing, same job as on a shingle roof.
  3. Underlayment. On the tile roofs we build, a self-adhered (peel and stick) membrane. This is the layer that keeps water out of the house.
  4. Battens. Wood strips the tile hooks over, on many tile roofs.
  5. Concrete tile, fastened. Tile sheds most of the water and shields the underlayment from the sun. Fasteners and battens hold it in place.
  6. Ridge and hip tile. Closes up the peaks and the hips.
Illustration of a typical assembly with the layers pulled apart so you can see each one, not a drawing of a specific roof. The exact products and layers on your roof are named in your contract.
The one most people miss

Why Tile That Looks Fine
Can Still Leak

Concrete tile is tough. In my experience it usually outlasts the underlayment under it. From the street the tile can look like the day it went on, while the layer underneath has dried out, cracked or torn, and that hidden layer is the one keeping water out of the house.

So an honest tile inspection looks under the tile, not just at it. When the tile is still good and the underlayment is not, you don't need new tile. That is exactly what a lift and relay is for: your own tile comes up, new underlayment goes down, and the same tile goes back on.

Roof deck with water staining along the seams, exposed during a tile roof repair under solar panels in Rancho Cucamonga
Water staining along the deck seams, found under tile during a repair in Rancho Cucamonga. From the ground, that roof looked fine.
Six parts that matter

The Parts That Matter Most

If you only learn six words about your roof, learn these. They are where leaks start and where a cheap bid usually saves its money.

Roof Deck

The wood everything is nailed to. Nobody knows its real condition until the old roof is off, which is why our contracts put a wood allowance in writing instead of guessing.

What's under your roof →

Underlayment

The layer that actually keeps water out. A self-adhered membrane seals around the nails that go through it, a backup old felt never had.

Felt vs. modern underlayment →

Flashing

Metal where the roof meets a wall, a chimney or an edge. Flashing is the seal. Caulk smeared over a gap is not flashing, it's a delay.

Why caulk is not flashing →

Valleys

Where two slopes meet, the valley carries the water off both. It needs an open channel. Tile run too far into it turns it into a dam.

Why valleys leak →

Penetrations

Every pipe, vent, skylight and solar mount is a hole in the roof. Each one needs its own flashing. On tile, that means a flashing at the tile and another at the deck.

Solar mounts and your roof →

Ventilation

Hot attic air needs a way in low, at the eaves, and a way out high, at a ridge vent or low-profile vents. Without it, the attic bakes the roof from below and the heat comes back into the house.

The attic that hit 157 degrees →
What right looks like
New OSB deck going down over old skip sheathing during a tear-off in Colton
New OSB deck over old skip sheathing, Colton tear-off.
Open tile roof valley with new ribbed metal and the tile cut back on both sides, Yorba Linda
An open tile valley: new metal, tile cut back on both sides. Yorba Linda.
New flashing around a skylight on a finished GAX tile roof in Yorba Linda
New flashing around a skylight on a finished tile roof. Yorba Linda.
Roof shapes

Know Your Roof Shape

Roof shapes at a glance. Shape describes the roof's form, not the material covering it.

Orange gable roof with a triangular end.

Gable Roof

Two sloped sides meet at a ridge above triangular end walls.

  • Two roof planes
  • Triangular ends
Orange hip roof sloping on all four sides.

Hip Roof

Four sloping sides meet at hips and a short ridge.

  • Four sloping sides
  • No gable ends
Orange low-slope roof on a rectangular building.

Flat or Low-Slope Roof

A nearly level roof surface with a slight slope for drainage.

  • Low profile
  • Slight drainage slope
Orange shed roof with one sloping plane.

Shed Roof

One continuous roof plane slopes from a higher wall to a lower wall.

  • One roof plane
  • Unequal wall heights
Orange gambrel roof with a broken-pitch gable profile.

Gambrel Roof

Two roof sides each change pitch, with vertical gable ends.

  • Two double-pitched sides
  • Barn-like end profile

Illustrations use GAX brand colors to highlight shape. They are not product color samples or construction details.

When to call

Warning Signs Worth a Call

None of these alone tells you what a roof needs. They tell you it's time for someone to get up there and look.

Aged shingle roof with heavy granule loss, inspection in Riverside

Shiny, Bare Shingles

When the granules wear off, the shingle looks shiny and the fiberglass mat shows through. In my experience, that roof is near the end of its life.

From an inspection in Riverside.
Read about granule loss →

Cracked or Slipped Tile

A few cracked tiles can be swapped. A lot of them, or tile sliding out of line, is a reason to look at what's underneath.

How long tile roofs last →
Counter flashing face-nailed flat against a brick chimney with exposed fastener heads, found on an inspection

Nailed or Caulked Flashing

Nail heads through the face of the metal and caulk where metal should be lapped are shortcuts that leak later.

Found on an inspection.
Caulk is not flashing →
Rake edge of a Highland roof showing three or more layers of shingles stacked over the drip edge, found on an inspection

Layers Stacked at the Edge

More than one layer of shingles hides the deck and adds weight. On every shingle job we do, all of it comes off. We'll look at yours and tell you how many are up there.

Three or more layers, Highland inspection.
Overlay vs. tear-off →
Thermal camera image of a ceiling showing a cold spot where water had soaked in

Stains or Wet Spots Inside

A thermal camera can show a cold, wet spot in a ceiling. The attic confirms it. The stain is rarely right under the leak.

A thermal camera finds it; the attic confirms it.
How we find a leak →

Leaks That Keep Moving

One patch, then a new leak somewhere else, usually means the underlayment is done, not that you've had bad luck.

Why the leak came back →
What it actually needs

Repair, Lift and Relay,
or Replacement

We decide on the roof, not over the phone, and not by the age of the house alone. Here is what usually points each way.

Repair

When the damage is isolated

A few shingles off after wind, one failed pipe boot, flashing pulled away from a chimney, on a roof that is otherwise sound.

Roof repairs →

Lift and Relay

When the tile is good and the underlayment is not

Your own tile comes up, new underlayment goes down, the same tile goes back on. You keep the look and fix what failed.

Tile lift and relay →

Replacement

When the roof itself is worn out

Shingles past their life, or leaks that keep showing up in new places. On shingles that is a full tear-off. On tile, a tile replacement with new tile.

Roof replacement →

Flat sections have their own systems (most get torch-down modified bitumen; TPO, PVC or EPDM when a roof calls for one). See flat roofs, and if you're weighing the options, repair vs. replacement walks through how we think it through.

If you want a straight answer about your roof, we'll come out, get up there and show you what we find, with photos you keep. Asphalt shingle roofs, tile replacement with new tile, tile lift and relay, and flat roofs, across the Inland Empire.

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Sources

Pages checked October 5, 2026. Everything else on this page comes from what we see on our own jobs.

Want to know what's under yours?
We'll get up there and show you.

(909) 819-8394