Do palm trees make roofs dirtier?

Start with what no document read has measured. The Tile Roofing Industry Alliance names the variables that affect growth on a tile roof, and the kind of tree is not one of them.

TRI Alliance writes that “many environmental variables affect the potential for this organic growth, including location of the structure, the direction the roof is oriented to the sun and the quantity of trees, canals and lakes in the area.” Quantity of trees is on that list. Which kind of tree is not.

The Asphalt Roofing Manufacturers Association describes what overhanging branches do in a bulletin written for asphalt shingle roofs, and it names no species.

ARMA writes that “overhanging tree branches provide additional shade and drop debris on the roof that further holds in moisture and acts as a food source for moss.” The same bulletin lists “trimming tree branches back to allow more sunlight to reach the roof and minimize debris accumulation” among the steps that discourage moss and algae, as a step for the owner to take.

Nothing in that mechanism names a tree. Shade keeps sun off the plane beneath it, and debris holds moisture against the surface, so any tree that overhangs a roof can do both. The full account of roofs getting dirty under the trees covers every kind of canopy together.

The one primary document read that describes a palm's own habit is UF/IFAS Extension's sheet on the queen palm.

UF/IFAS writes that “fruit drop is a major concern for queen palms because fruit clusters can weigh over 100 pounds and contain over a thousand seeds.” The same sheet adds that queen palms “are not considered to be self-cleaning, so every leaf must be manually cut off after it dies,” with the flower and fruit stalks typically removed at the same time “to reduce the mess caused by falling fruit.”

So a queen palm near a roof has two documented habits: heavy fruit that falls, and dead leaves that stay on the tree until someone cuts them. No source read measures either habit against growth on a roof, or compares a queen palm's debris with any other tree's.

On a tile roof, TRI Alliance places the growth on what settles on the tile rather than on the tile itself.

Mildew, algae and moss, TRI says, grow on “the accumulation of dust and other organic materials that settle on tile.” Fallen fruit and leaf litter are organic material, but TRI does not name palm debris, and no source read says one tree's litter feeds more growth than another's.

UF/IFAS's instruction that every dead leaf be cut off is palm pruning, and pruning is tree work.

Where a canopy needs cutting back from a roof, or a queen palm's dead leaves and fruit stalks need removing, an arborist or a tree service is the trade to ask. ARMA lists trimming branches back among the steps an owner can take; it does not say who does the cutting.

Palm trees are one part of a bigger question about anything overhanging a roof.

ARMA says algae discoloration should not be confused with moss or tree droppings, which “typically produce only localized discoloration,” unlike the black streaks algae can leave. Whether a roof cleaning also clears leaves and debris is its own question, and what collects in a roof valley is part of the under-trees account.