Gutter & Downspout sizing

[shooon]

Just had a contractor come install gutters and downspouts on the new shop. I was under the impression each gutter would have its own independent downspout, but it looks like he tied the two gutters into a common downspout and "T'd" into the one side.

We've had some crazy rain and flooding up here the past few years, within the 110mm + over a couple days type deal. Not sure what the max mm/hr or GPM equivalent was though.

It looks better ascetically the way he installed it... Just wondering if based on roof specs this is going to be adequate or if I need to split them into separate spouts as originally thought.

Roof area: 1100 sq.ft (550 per gutter)
Roof pitch: 4/12
Gutter length: 36' 5" K style per side (2x)
Downspout length side 1: 3x elbows 12' of corr. square pipe 3x4"
Downspout length side 2: 1x elbow 30' of corr. square pipe 3x4"

What do you guys think?

 

[kbs2244]

It isn't the length of the pipe, it is the size.
I would want 4x6, or even 6x8 pipes for that amount of roof.

And what about he gutters them selves?
Where they oversized?

To get an idea of what you need go behind a store in your area with the same sized roof.
You will see a professionally sized, and inspected, set up.

 

[lakeroadster]

What do you guys think?

I think the internet is awesome... Gutter Size Requirement Calculator

Assuming Seattle rain data and then running the numbers... looks like you are ok as is.

 

[shooon]

I think the internet is awesome... Gutter Size Requirement Calculator

Assuming Seattle rain data and then running the numbers... looks like you are ok as is.

Thanks!

I found that same calculator and couldn't make sense of it once I punched everything in. Figured I might get clarity from the people of the forum

 

[lakeroadster]

Thanks!

I found that same calculator and couldn't make sense of it once I punched everything in. Figured I might get clarity from the people of the forum

Your welcome. FYI: This is the data I used..