The Section That Did Not Make Sense
Same Riverside inspection where we found the spot-nailed tile, different problem, and this one was the builder's. Part of this home's patio roof is flat. And running right onto that flat section, laid down like it was any other part of the roof, was concrete tile. You can see it in the photos: the tile courses just flatten out and keep going. It does not make sense, and the roof has spent years proving it.
Why Tile and Shingle Need Pitch
Tile and shingle work the same way: they are overlapping layers that shed water downhill. Gravity is part of the system. Water hits a tile, runs down onto the next one, and exits at the gutter. Take away the pitch and you take away the plan. On a flat section, water does not run off. It sits, and it backs up underneath the overlaps, straight into the felt. Regular felt under tile is built to handle the little bit of water that sneaks past on a sloped roof. It is not built to be a swimming pool liner.
What Years of Backed-Up Water Did
Walk under this patio and look up. The roof deck is not just stained, it is rotted through and caving in, with openings you can see daylight through. That is what standing water does when it has years and nowhere to go.
The one piece of luck in this story: it is an outdoor patio. The rot is happening over the barbecue, not over a bedroom. Same physics on a flat section over living space and this is a very different conversation.
What Actually Belongs on a Flat Roof
Flat and low-slope sections need a system that seals instead of sheds: a torch-down system, granulated base and cap sheets over 75-pound felt, built as a continuous waterproof surface. Water can sit on it, think about life, and evaporate, and nothing underneath gets wet. That is the difference: sloped systems shed water, flat systems seal it out.
The Fix Here
For this patio, the repair is honest and specific: the rotted deck gets a resheet, new plywood over that section, and the tile comes off the flat area for good, replaced with a proper torch-down flat roof system. Tile stays where it has pitch, flat roofing goes where it is flat, and every material does the one job it was designed for.
If your home has a flat patio cover, porch, or room addition wearing tile or shingles, go take a look at the underside. The deck will tell you the truth before your ceiling does.