Gutters and downspouts

Does anyone have a good rule of thumb for distance between downspouts?
I am at an inspection (new construction) with a roof pitch of 12/12 and there is a distance of about 100 feet between downspouts.:shock:

I think that they recommend a down spout every 30 ft.

That’s what I thought as well, but this is the third new construction house I’ve seen like this in a month.:roll:

I believe distance between downspouts may be subject to local ordinance, but don’t quote me. :wink:

depends on how much roof surface it’s serving.
i think i read 1 rainleader per square of roofing

This might help.



Did they have kickout diverters?

No, no kickouts. I would also think the roof surface area would play a part in the amount of downspouts.

The correct answer per SMACNA is typically 40 feet maximum distance. This is assuming a 2" x 3" downspout leader pipe. The rain tables in the SMACNA manual also would further weigh on the distance.


A lot of new construction in my area has the upper roof downspouts spilling onto the lower roof and then into the lower gutters. Use some common sense when making this type of determination. There may be no definite rule to go by.

There’s nothing more stupid than 1/2 of a roof over a 2 story, 3000 sf house that has to drain everything through 2 downspouts. Poor design, poor installation.

On asphalt shingles especially, that practice will cause premature wear where the concentrated water load is on the lower roof.

In our neck of the woods I was taught to go by the rule of 20-25 feet for a 4" gutter and 30-35 feet for a 5" gutter system. Seems reasonable to me.

We are very close to as area of Vancouver Island known to have one of the highest rainfalls in North America, 27 feet per year (Kildonan, B.C.).


Is it “right” because everyone is doing it?
I believe a D/S for every 40 ft of gutter is recommended. It may be worth a call to the builder(s) and ask them why.


Interesting thread, below is my standard gutter comment.

Here is a link from pathnet regarding this topic.

CHAPTER 4 - Rain and Water Vapor


“The rain tables in the SMACNA manual also would further weigh on the distance.”

I’ll scan then from my copy and post them the next time I’m in the office.


Thats the tables I mentioned in my earlier post, but someone swiped my SMACNA manual and it is not available free online upon a very short search.

If I tried harder, I’m sure I could find them, but I would appreciate the copy that you could scan, with any pertinent data and conditions, such as pitch factors and the such.


Thanks for the link, Ed.
North Witcher
Omaha, NE