Tile Roofs on a South San Francisco Hillside: Weight, Slope, and Doing It Right
Tile sets the look on many South San Francisco hillside streets, but it asks more of a roof than asphalt does. Here is what weight, slope, and the underlayment underneath really mean for a tile roof here.
Why tile suits the hillside, and what it asks in return
Tile is a familiar sight on the South San Francisco hillsides, and for good reason. It suits the look of many of the homes and streetscapes here, it stands up well to the coast, and a tile roof done right can last a very long time. But tile is not asphalt, and treating it as if it were is one of the more common and more expensive mistakes a homeowner can make. Tile asks more of the structure beneath it, more of the install, and a different kind of attention over its life, and getting any of that wrong turns a long-lived roof into a recurring problem.
The first thing to understand about tile is that the tile itself is not really what keeps the water out. People assume the tile is the waterproof layer, but on most tile roofs the tile is the durable, weatherproof shell that protects the layer underneath, and it is that underlayment that actually keeps the water out. This single fact explains most of what is misunderstood about tile roofs, and it is the key to understanding why a tile roof can start leaking while every tile on it looks perfectly intact.
Weight, structure, and slope
Tile is heavy, far heavier than asphalt, and that weight has real consequences on a hillside home. A roof structure has to be built or verified to carry the load of a tile roof, and you cannot simply swap a light asphalt roof for tile without confirming the framing beneath can handle it. On the varied hillside builds of South San Francisco, with their multiple levels and additions worked into the slope, that question of whether the structure can carry tile is not academic, and it is one of the first things we look at when a homeowner is considering tile on a home that does not already have it.
Slope matters too. Tile sheds water by overlapping pieces channeling it downhill, and that system depends on the roof having enough pitch to move water along quickly. On a steep hillside roof tile works beautifully, but on the lower-slope sections that some homes have, tile is less forgiving, because water moves more slowly and has more chance to find its way to the underlayment. On a roof that mixes steep and low-slope areas, which a lot of complex hillside homes do, the right answer is sometimes tile on the steep sections and a different system on the low-slope ones, rather than forcing tile everywhere and creating a weak point.
- On most tile roofs, the underlayment keeps water out, not the tile
- Tile is heavy and the structure must be able to carry the load
- Steep hillside slopes suit tile; very low slopes do not
- A mixed-slope roof may need tile on the steep parts only
- Tiles can outlast the underlayment beneath them by decades
The underlayment is the roof you cannot see
Because the underlayment is what actually keeps the water out, the lifespan of a tile roof is really the lifespan of that underlayment, and here is where many tile-roof homeowners get caught out. The tiles themselves can last a very long time, often far longer than the underlayment beneath them. So a tile roof can reach a point where the tiles look fine, even excellent, while the underlayment underneath has aged out and started letting water through. The roof leaks, the homeowner is baffled because the tiles look perfect, and the real problem is invisible underneath.
When that happens, the job is not a simple repair. The tiles have to be carefully removed and set aside, the old underlayment stripped, fresh underlayment laid down, and the tiles, the sound ones at least, reinstalled, with broken or unusable tiles replaced. It is a substantial job, but it is the job the roof actually needs, and on the coast it is one that comes around because the marine damp and salt work on the underlayment and the flashing beneath the tile just as they do on everything else. An honest tile inspection here reads the underlayment and the flashing, not just the tiles, because that is where a tile roof's real condition lives.
There is also the matter of walking a tile roof. Tile cracks underfoot if it is walked carelessly, so inspecting and working on a tile roof takes a crew that knows how to move on it without breaking it. A roof that comes back from a careless inspection with a trail of cracked tiles has been made worse, not better, and replacing those cracked tiles becomes its own small repair. This is one more reason a tile roof rewards a crew that actually knows tile rather than one that treats it like any other surface to stand on.
Doing a tile roof right on the coast
Doing a tile roof right in South San Francisco comes down to respecting what tile is. Confirming the structure can carry the weight, matching tile to slopes that suit it, installing a quality underlayment that is the real waterproof layer, using corrosion-resistant flashing that will not give out before the tile does, and maintaining the roof with an understanding that the tiles and the underlayment age on different schedules. Do all that, and a tile roof on a South San Francisco hillside is one of the longest-lived roofs you can have.
Skip any of it, and tile becomes an expensive disappointment, leaking despite intact tiles, cracking under careless feet, or sitting too heavily on a structure that was never verified to carry it. The material is not forgiving of shortcuts. When we work on tile here, we treat it as the long-term system it can be, which means reading the underlayment and the structure honestly and telling you what the roof actually needs, even when that is more than a homeowner hoping for a quick tile swap wanted to hear.
A tile roof can outlast almost anything when it is done right, and disappoint when it is not. If you have tile on a South San Francisco hillside home, call 650-431-1123 for a free inspection that reads the underlayment and the structure, not just the tiles.
When you are ready, call 650-431-1123 for a free roof inspection.