How many downspouts for a 60x80 barn

[camnick]

I just had a 60x80 barn built. I am about to have gutters and downspouts installed. They recommended 4 on each side. Is this overkill? I am going to bury the downspouts. Will a 4" corrugated pipe be large enough to flow all that water away from the barn? hopefully someone has run accross this problem.

 

[tinbender 66]

If it's the 80' length that the gutters go on then 4 is about right. Any thing over 50' should have an expansion joint also. So you basically end up with two gutters on each side. My experience is in commercial architectural metal so YMMV. As for the corrugated, I don't really know but from the jobs I've been on it should work. Don't know how much rain you get though.

 

[kbs2244]

Go with the 4 down spouts.
And go with 6 inch, not 3 inch.
That is a whole lot of roof.

I had a commercial "flat roof" building your size with the roof drain plumbed with 3 inch across the street from where I once worked. The exit came out about 3 foot above ground level onto the parking lot that was slopped to a creek.

It worked fine with a slow gentle rain. But with a hard spring thunder storm the water would jet out 4 feet before hitting the ground.

Do the math.
You have 4800 sq. ft. of roof.
That is 57,600 sq. in. of roof.
So a one inch rain is 57,600 cu. in. of rain.
At 1728 cu. in. to a cu. ft. that is 33.3 cu. ft. of water.
A cu. ft. of water is 7.5 gallons.
So 7.5 times 33.3 means a one inch rain is 250 gallons of water.

In central IND how often do you get 2 and 3 inches of rain in less than a hour?
Where is that water going to go?
Do you have a field drain tile nearby?

 

[jimp]

I have a 60X80 shop in KC area. It has 6 total (3 each side) 6" down spouts. They seem to be more that enough.

 

[camnick]

I have a drainage ditch, but it's about 400 feet away. I was thinking about running a 6" pipe to the drain and tie in all the downspouts. Hopefully the 6" pipe will flow enough.

 

[kbs2244]

Yeah
6 inch from top to bottom.

 

[Eric Commarato]

I am a registered architect that has been in practice for 25 years. We always base gutter sizing here in the south on a 4" per hour rain. Seems like a lot, and though very rarely would happen non the less you have to prepare for this type of storm. We usually use a chart in Architectural Graphic Standard along with a set of formulas that takes into account roof pitch, area etc. I can scan this and post it if you would like. A 4" downspout and take a motherload of water. I sounds like you are fine with the number...overkill??? I rather be safe than sorry.

 

[PhantomEB]

And with that amount of roof/gutter, why not invest in a few rain barrels, I have always invisioned my future 32x72 shop having them at each corner as well in the center of the 72, possibly two, never hurts to have free water when you need it.