I've recently started smelling a musty smell in my upstairs bedroom. The bedroom closet just happens to be where the downspout from the main roof drains onto the roof for my garage and creates a kind of corner in the roof. As I have been looking into it, how the downspout has been configured feels completely wrong.

Is there any way this makes sense? Why angle to downspout into/up the slope of the shingles as opposed to out and across the slope/away from the siding?

downspout angle downspout angle 2

  • 3
    Once you have or even before you have that downspout directed away from there, check to make sure that corner is sealed tight or have the sealing redone. That corner might hold onto water and cause leaks into the house.
    – crip659
    Commented Mar 19, 2023 at 21:49
  • 2
    I’ve got the company that installed the gutters and redid the roof coming this week for a warranty repair. I plan on having them reassess the flashing and siding as well. The wood siding definitely needs to be replaced as I t falls apart just by touching it with my finger.
    – philmonroe
    Commented Mar 19, 2023 at 23:45
  • 8
    @philmonroe I'd be getting them to remove the shingles, check and repair if necessary, the probably rotten substrate, as well.
    – SiHa
    Commented Mar 20, 2023 at 7:21
  • 7
    Why install like that? Most likely because that was the last elbow they had on the truck and it was easier to put that on there than it was to go to back to the shop to pick up the right part.
    – FreeMan
    Commented Mar 20, 2023 at 15:59
  • The intention MAY have been to stop a large flow overtopping the lower edge. If so, a solid sheet on top of the shingles would have stopped water being driven up and under them. Commented Mar 21, 2023 at 12:44

3 Answers 3


It's completely wrong!

The shingles overlap each other. This ensures that water running from top down doesn't enter under them.

When you flush water against the overlapping sections, they are not water proof. Water may enter under the top shingle.

You should ensure that water flows from shingle on top to shingle under it.

  • Don't know how much water it carries: downspouts can carry a lot of water and eject it with a fair amount of force. Not only don't you want it running up against the shingles, you don't want it running across them either. Frankly, you shouldn't let that water run onto a roof at all (rubs granules off). You should add downspouts to get it to the ground (perhaps run it into that lower gutter). Commented Apr 14 at 21:05

Get it out of that corner and have the water flow downwards not upwards under the shingles guaranteed to leak.

You just need one more part.

Downspout Side Elbow



  • 2
    There are Type A and Type B elbows, and this has the wrong one. But even with the correct type, you'll still need at least one more elbow and an extender section to ensure that the outflow is directed downward and not across the shingles. (Across isn't as bad as upward, as it is now, but it's still wrong.) It that's hard to set up, you might consider a Flexible Downspout Extension. Commented Mar 20, 2023 at 2:42
  • 7
    I might argue that the OP needs two elbows—a B elbow attached to the downspout, and an A elbow attached to the B elbow, to turn the water more downslope than across slope.
    – Huesmann
    Commented Mar 20, 2023 at 12:18
  • OP already has the A elbow - I think this answer implies it's to be re-used below the added B elbow, but it could make that clearer. Commented Mar 23, 2023 at 16:35

That down spout is the termination point for ALL the rain water on that side of the roof! All that water is being directed to a small area and shot against the overlap of the shingles.

Do yourself a favor and remove all the gutters and downspouts on the second floor. Let the roof shed the rain as it was designed to do and let the lower roof collect the rain. You then don't have all that water concentrated in one small area.

  • 2
    To clarify: there are other downspouts from the primary/second story roof as well. Some go to the other side of the lower garage roof, while others go all the way to the ground. I would estimate that this downspout gets 1/8 to 1/6 of the rain off the primary roof. It’s still quite a bit of water though…
    – philmonroe
    Commented Mar 20, 2023 at 1:05

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