Lisa asked, "I heard that when rainwater mixes with pigeon excrement it becomes acidic and it is a common cause of roof leaks (mixture eats through the waterproof underlayment). Is this true?"
I asked Ian Hollandsworth from Ruffle Feathers Bird Control in Sacramento this question. If anyone could answer this question he could, being in the bird abatement business for many years.
"Hi Bob, It is true that pigeon droppings are acidic and can cause damage to roofing materials but it happens over a long period of time. What more commonly happens is droppings pile up and can trap or divert water on the roof or block up the gutters causing damage and leaks. You are more likely to see water damage caused by a build-up of pigeon droppings than you are to see damage from the acidity of the droppings. I hope that helps!"
So, Lisa, it looks like your bird's droppings are acidic and can cause damage to the roofing if left unattended for a while. The droppings can dam up the water flow around flashings, chimneys and valleys, filling things up and clogging things bad enough that water moves sideways causing leaks. They can also affect your rain gutter system, causing water to back up and overflow, damaging the wood along the eaves of your home. Birds, nesting material and droppings leave an unsightly mess and detract from the appearance of your home.
I would also be concerned with humans contacting the disease-infested run-off around the downspout area where children may play in the yard.
Here's a tip for a better roof - Never install a skylight under an antenna, or vice-versa. The birds gather and drop their bombs all day on the skylight. This looks horrible from the inside looking out and needs cleaning every day.
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