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Posted by z on November 7, 2005, 11:08 am
Dan_Musicant wrote:
> My roof (2 story, 1925 square foot house) was just replaced and I heard
> the project manager and crew chief debating whether I needed one or two
> downspouts for the bottom roof. On the front of the house, everything
> from the ridge forward drains toward the front. That includes a large
> dormer (2nd story), whose downspout drains directly onto the lower roof.
> Water from that flows down about 5 feet of 50 year asphalt composition
> shingles into the gutter on the lower roof where it meets the runoff
> from the lower roof. The debate was whether one or two downspouts are
> needed from the lower gutter and the project manager decided on one, at
> one side. I wonder if this is enough. I also wonder if there shouldn't
> be an extension of downspout from the dormer roof directly to the lower
> gutter so all that water doesn't run down one part of the lower roof for
> 5 feet.
> The total area of roof forward of the ridge is something like 700 square
> feet and all that going down one downspout (standard size aluminum, I
> figure around 7 square inch cross section) seems like a lot to expect of
> one downspout in a heavy rain. What is the situation? Is there a website
> I can go to to figure out downspout requirements for a given roof area?
> Thanks for any help.
> Dan
Between the normal size and oversize gutters typically available at
Home Depot or Lowes, if you can manage to adapt the larger size
downspout to a regular size gutter, you get a lot better drainage and
freedom from clogging. Often just enlarging the hole in the bottom of
the gutter and dropping in one of the separate oversize outlets will
work. depending on how the gutter is shaped.
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> the project manager and crew chief debating whether I needed one or two
> downspouts for the bottom roof. On the front of the house, everything
> from the ridge forward drains toward the front. That includes a large
> dormer (2nd story), whose downspout drains directly onto the lower roof.
> Water from that flows down about 5 feet of 50 year asphalt composition
> shingles into the gutter on the lower roof where it meets the runoff
> from the lower roof. The debate was whether one or two downspouts are
> needed from the lower gutter and the project manager decided on one, at
> one side. I wonder if this is enough. I also wonder if there shouldn't
> be an extension of downspout from the dormer roof directly to the lower
> gutter so all that water doesn't run down one part of the lower roof for
> 5 feet.
> The total area of roof forward of the ridge is something like 700 square
> feet and all that going down one downspout (standard size aluminum, I
> figure around 7 square inch cross section) seems like a lot to expect of
> one downspout in a heavy rain. What is the situation? Is there a website
> I can go to to figure out downspout requirements for a given roof area?
> Thanks for any help.
> Dan