Solar on a Tile Roof: What Changes, and What Breaks

Tile roofs are the default across much of the Southwest, Florida and coastal California — which is to say across much of where residential solar is installed. They are also the covering on which a solar installation is most likely to produce an argument, and the argument is almost never about the panels.

It is about tiles. How many broke, who replaces them, and what happens when the ones that broke are no longer made.

Three properties of tile, and everything follows from them

Tile is brittle. Clay and concrete tile is strong in the direction it was designed to be loaded and fragile in most others. Weight applied to the unsupported part of a tile cracks it. Every person who has ever been on the roof — the surveyor, the installer, the inspector, the service technician five years later — has applied weight to it.

Tile is heavy. A tile roof imposes a substantially larger dead load than an asphalt shingle roof of the same area, and the framing under it was designed for that load. Adding an array to a structure already carrying the heaviest common residential covering is a different structural proposition from adding one to a shingle roof.

Tile is hard to match. Profiles and colours are discontinued. Weathering shifts colour over decades, so even the same model from current production rarely matches a twenty-year-old roof exactly.

Nothing else about tile matters as much as these three, and they explain every clause that ought to be in the contract.

What the code requires

The International Residential Code treats clay and concrete tile in Section R905.3, and three of its requirements bear directly on a solar project.

Slope. Section R905.3.2 permits tile on slopes of 2½ units vertical in 12 units horizontal or greater. Between 2½:12 and 4:12, a double layer of underlayment is required rather than a single layer — the same two-tier structure the code applies to asphalt shingles, which sit at a 2:12 minimum under R905.2.2 with doubled underlayment below 4:12.

Deck. Section R905.3.1 requires tile to be installed over solid sheathing, with an exception permitting spaced lumber sheathing in certain seismic design categories. This matters to an array because the mount has to reach a structural member regardless of what the covering is, and the question of what is under the tile is not one to discover from the roof.

Underlayment. Section R905.3.3 sends the underlayment requirement back to Section R905.1.1, where the required type depends on the wind design conditions at the site.

The section numbering moves between editions and jurisdictions amend Chapter 9 freely, so treat these as the shape of the requirement and confirm the detail against the edition your building department has adopted.

The rule that surprises people: a tile roof cannot be recovered

Most roof coverings can, in defined circumstances, have a new covering installed over the old one instead of a full tear-off. Tile cannot.

Section R908.3.1.1 prohibits a roof recover where the existing roof covering is slate, clay, cement or asbestos-cement tile. It is an unconditional prohibition sitting in the same list as the water-soaked-deck condition and the two-existing-layers condition, and it is not relieved by a new covering's manufacturer instructions permitting a recover in general. The full R908 picture sets out how the permissions and prohibitions interact.

The consequence for a solar decision is direct. On a shingle roof there is at least a theoretical cheaper path at end of life. On a tile roof there is not: it is a tear-off, the array comes off for it, and the array goes back on afterwards. That is the most expensive routine sequence in residential solar, and it is why the roof's remaining service life belongs in the conversation before the array is fastened down rather than eight years into it.

How the array actually attaches

A mount cannot bear on the tile. Tile is a covering, not a structural element, and loading it is how it breaks. Two details dominate, both covered in more depth in how solar panels attach to a roof:

• A tile replacement flashing. A tile is removed and a metal pan shaped to the tile profile is substituted in its place. The mount passes through the pan, which carries the water over the course below.
• A tile hook. A bracket is fastened to the rafter and reaches out from under the tile above, so the original tile can sit back down over it. Nothing is substituted, but the hook has to clear the tile without holding it up off its seat — a hook that lifts the tile above it creates a high spot that cracks under the next footstep.

Both are designed so the waterproofing layer stays continuous and the tile carries no load. Both also require that somebody lifted tiles to fasten into the rafter, which means the tiles came off and went back on, which means some of them broke.

Breakage is a consumable, not a scandal

This is the point most worth internalising, on both sides of the transaction.

Breakage on a tile roof is normal and expected. A crew that breaks zero tiles on a full array installation is unusual. Competent practice reduces the count considerably — walking the supported lower portion of each tile, using walk boards to spread load, planning access routes so the same tiles are not crossed repeatedly, staging materials off the roof — but the realistic target is a manageable number, not none.

Because it is normal, it should be priced and written down rather than treated as damage to be argued about afterwards:

• Who replaces broken tiles, and whether the number is capped.
• Where the replacements come from — contractor stock, the homeowner's attic stock, or purchase.
• What standard of match is acceptable where an exact one is unavailable.
• What happens if no match can be sourced at all.

That last one is the clause nobody writes and everybody needs. It is also the reason to establish before the crew arrives whether the tile is still in production, and to locate any leftover tile the original roofer left in the garage or on the side return.

When breakage becomes a liability question instead

There is a line between expected breakage and damage, and it is usually crossed in one of three ways: the quantity is far beyond what the work required, the breakage is concentrated somewhere that suggests a specific incident, or a broken tile let water in and the consequence is now a ceiling rather than a tile.

At that point it stops being a contract-scope question and becomes the subject of who is liable if a solar installation damages your roof — a different route, with different remedies, and one that is far easier to travel if somebody photographed the roof before the work started. Where a roofing contractor and a solar contractor have both been on the same tiles, establishing which trade broke what is close to impossible retrospectively. A dated set of before-photographs costs nothing.

The bottom line

Tile does not make solar difficult. It makes three specific things true that a shingle roof does not: some tiles will break, the roof can never be recovered so its end of life is always a tear-off with the array coming off for it, and the covering's weight makes a structural review likelier than not.

All three are manageable at design and contract stage, and all three are expensive to discover at the end. The single most useful thing a homeowner can do before a tile roof is worked on is find out whether the tile can still be bought.