Tie deck drain and downspout drains together?

Cluckr7

Active member
Jun 19, 2020
37
Texas
Is it ok to have a common drain to the street for both my deck drain and my downspouts from the roof?

It would be a main 4” PVC pipe to the street, with 4 roof downspouts and the deck drain feeding it.

I think it’s probably a 1-2 foot elevation drop from the first downspout to the street. All the other downspouts and the deck are roughly the same elevation.

I wasn’t sure if this is a typical practice, or if the preference is to have separate drains for the deck vs roof downspouts. Would there be a chance the roof downspouts would actually hydraulically back into the deck drain in very heavy rain?
 

tim5055

Mod Squad
TFP Expert
LifeTime Supporter
May 11, 2014
10,996
Franklin, NC
The first thing to look at is if your jurisdiction has any rules regarding discharging storm-water to the street. Many jurisdictions have passed local ordinances requiring storm-water to be retained on the property.


Once past that, then yes, if the discharge pipe to the street was overloaded then the deck drain being the lowest opening would become a discharge for the downspouts.
 

Cluckr7

Active member
Jun 19, 2020
37
Texas
Thanks for the response Tim.

My municipality allows (maybe requires I think) draining to the street and all the houses here are built with downspouts that drain the the street.

My existing underground pipe is that black corrugated stuff that I believe is crushed somewhere because all of my downspouts overflow and I see very little water at the street end. Also I have replace one segment of crushed pipe with rigid PVC already, I guess there’s at least one other area of crushed pipe.

Anyway, I am about to build out a new pool and also want to replace this entire length of black corrugated drain pipe that basically runs the entire length of the side of the house back to where the pool will be.

So I’m trying to figure out if I should get a landscaper to replace my existing drain pipe, and independently have the PB install a new and separate drain that would basically run parallel. And if these are separate, is there a right sequence?

Or if would be smart / OK to have everything tie to a common drain and just ask the PB to tie in the downspouts to his drain pipe.
 

tim5055

Mod Squad
TFP Expert
LifeTime Supporter
May 11, 2014
10,996
Franklin, NC
I personally don't see a problem with tieing them together, but would probably go with larger pipe, maybe 6".

Another thing to look for is restrictions on draining pool water to the street. This is another area some jurisdictions are restricting, usually with no understanding of pool water or chlorine. A friend built a pool a couple of years ago and put in a sand filter (my favorite, wonder where he got the idea). His jurisdiction prohibits teh discharge of pool water to the street and storm drains unless there is a system in place to remove the chlorine before it is discharged. But, they exempt Salt Water pools because as the inspector told me (I kept my mouth shut) they don't use chlorine.
 

CrystalRiver

Well-known member
Jun 19, 2020
234
Massachusetts
Four 2x3 downspouts have an area of 24 sq inches. A four inch pipe is half of that, at a bit over 12 sq inches. A six inch pipe is a bit over 28 sq inches. Water will flow quicker through the downspouts than through your horizontal pipe at the same cross sectional area, because of gravity.

If your gutters are 3x4, that's 48 sq inches.

I think you need a lot more than just a single four inch pipe. One for the deck and two for the downspouts, or a six inch for the downspouts and a separate one for the deck.
 

BowserB

Silver Supporter
Jul 29, 2018
324
Katy, Texas
My house has 9 downspouts, and two are in the back where they would have emptied onto or next to the pool decking (the others around the house just drain onto splashblocks or conduits through flower beds.) The PB tied the two into the pool overflow drain going to the street. Where we are, in the City of Katy, permits and inspections is, I think, all the city does. If the drains were a problem, they would have failed inspection. Since September 2018 we've not had a rain sufficiently hard to cause the drain to back up.
 

Cluckr7

Active member
Jun 19, 2020
37
Texas
Thanks all. I will chat with my PB to see if we can keep things separate just in case. Was hoping to avoid trying to coordinate landscaping and PB but maybe it just needs to happen
 

rphpool

Well-known member
Mar 4, 2015
675
Sugar Land , TX
My PB tied all my drain lines ( pool & house & yard ) together and they dump to street. We have had no issues except Harvey. It rained so hard , so fast that when streets flooded there was no where for the water to drain.