Q: Our house roof drains on our garage roof. Is this common and is it ok to do this?

A: I see this all the time. Builders are still doing this on new builds but I don’t recommend it. I can show you multiple examples of a roof that is otherwise in good condition but has a section under a downspout that has been ruined by the added water of an upper roof hitting it. In a heavy rain you can see the water pounding onto the lower roof. It is not surprising that this added water will shorten the life of the shingles. I often walk all over a roof and find an area that has only a couple years of life left while the rest of the roof would likely be fine for at least another ten years. To me it’s clear that draining an upper roof onto a lower roof is a bad idea.