How To Look At A House
McGarry and Madsen's home inspection blog for buyers of
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Is it alright for a gutter downspout from an upper roof to empty onto a lower roof?
Monday, July 22, 2019
It depends on who you ask this question. There is no building code citation that forbids a gutter from draining onto a lower roof. So it’s a matter of what the home inspector or contractor considers acceptable. Generally, a contractor that drains a gutter onto a lower roof will say that it is an “industry standard,” whereas a contractor that rants against it will say that it's “not best building practice.” And both have good arguments to backup their opinion.
Opponents say that the concentrated water flow wears away the granules faster in the lower roof where it drains across it, which is true. But it is also true that a woven (closed) valley takes a lot of water and loses granules faster than the rest of a roof, and closed valleys are not frowned on. Although the granule loss is noticeable after about 10 years, we have never seen a roof that needed to be replaced early because the granule loss was so significantly worse than the rest of the roof.
The one thing that pretty much everybody agrees on is that at least there should be a downspout to deliver the water to the lower roof and point it in the right direction. A hole at the bottom of the gutter or an open gutter end will just splash water around in a heavy rain. It is also not a good idea to drain down a lower roof too close to adjacent wall above the roof.
Then there is the aesthetic consideration. Some homeowners feel that a gutter running across a roof, especially at the front elevation, messes with the curb appeal of the house. The photo at the top of the page is one example of a upper gutter draining into a lower one neatly, coming down tucked around the side wall, and not calling attention to itself. So it can be done unobtrusively in some situations.
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To learn more about roofs and attics, see these other blog posts:
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