parking area drainage

[rieferman]

Hey GJ,
We're finally getting around to having our parking area (about 25 feet x 30 feet) paved by a local pro with many solid recommendations from people I know/trust.

In our case, we have no choice but for the parking area to pitch towards my yard and sidewalk that goes from our house to the barn, rather than out to the street. Trying to pitch towards the street would entail a very major overhaul to sidewalk, fencing, yard etc. Not in the cards.

In the past, rain had the opportunity to drain into the ground through the gravel. Once paved, that won't occur anymore.

We have underground 4" PVC pipes run for gutter drainage already near to parking area.

Our thought is to put in a drain box (say 12" x 12") at the low corner and direct the water to run there. We'll have to keep an eye on leaves/debris clogging etc.

Do you think a drain box of this size, running to 4" PVC pipe will be able to handle the run off from a 25x30 parking area? Any other words of wisdom?

Thanks!

Bob R.

 

[strutaeng]

Hey GJ,
We're finally getting around to having our parking area (about 25 feet x 30 feet) paved by a local pro with many solid recommendations from people I know/trust.

In our case, we have no choice but for the parking area to pitch towards my yard and sidewalk that goes from our house to the barn, rather than out to the street. Trying to pitch towards the street would entail a very major overhaul to sidewalk, fencing, yard etc. Not in the cards.

In the past, rain had the opportunity to drain into the ground through the gravel. Once paved, that won't occur anymore.

We have underground 4" PVC pipes run for gutter drainage already near to parking area.

Our thought is to put in a drain box (say 12" x 12") at the low corner and direct the water to run there. We'll have to keep an eye on leaves/debris clogging etc.

Do you think a drain box of this size, running to 4" PVC pipe will be able to handle the run off from a 25x30 parking area? Any other words of wisdom?

Thanks!

Bob R.

Sure, not a problem. Those catch basins can collect a huge GPM of water.

It's the drain pipe the limiting factor. What's the slope and distance of the pipe? Smooth or corrugated?

I've got a 12x12 catch basin collecting at least 500 square feet combined concrete driveway and roof. It's connected to 6" SDR 35 about 125' at about 0.5% slope. Works great. We had about 8" of rain in a single event last year, and never overflowed. It's sized for adfitional future drainage.

You can probably do 3" smoothwall with a 9x9 basin. The 12x12 drops the pipe about 4". NDS drains has a calculator online.

 

[rieferman]

Thanks for the input!

It will be smooth wall, non-perforated 4" PVC. It will be capturing a very small section of roofing (about 10x10) and this 25x30 driveway too.

Not sure of the slope of the pipe exactly, but it's roughly a 4 foot drop over the first 50 feet, a bend, then an 8 foot drop over the next 100 feet.

Currently, the gutters run into this system for about 10 years without any issues, but I wanted to think it through before adding the driveway (basically another roof).

I'll check out that NDS calculator too. Thanks!

 

[strutaeng]

That's a huge drop! That pipe will carry a lot of water!

It's a good idea to leave a cleanout in case it gets clogged. Probably won't get clogged from silt/sediment, but maybe some animal can get in and die.

For that length maybe 2. Cleanout near the inlet also serves for any future downspouts or other inlets. Those boxes also have this provision.

 

[Fix Until Broke]

Anywhere there's an elbow, put a Tee in instead with a cleanout.

 

[rieferman]

For sure. We have a clean out where the 50 foot section connects to the 100 foot section, and then we daylight at the top and the bottom too.

Thanks for the advice!!

 

[Bruce 993 SEA]

You should work REALLY closely with your contractor doing the paving to make sure your slopes all work to get the water to the drain.

In the past I have had some pretty poor results when the paving guys were left on their own. Too much slope with a low drain or uneven surface that leaves puddles.

I have had way better luck with concrete guys getting the slopes just right.

Sounds like you have some natural slope that will work to your advantage.

Cheers!

 

[theoldwizard1]

Years after it was installed, my driveway had a very slight pitch toward the house. The area was an odd shaped triangle, in some places 5' from the house and in other almost 20'. Never had any water in the basement but it was always soft/muddy. The base is mostly clay.

I had it dug out 1' deep and filled with broken concrete (2"-4") and 3/4" crush limestone. This was compacted. I planned on brick pavers for the top layer, so underneath them I had 4"-6" of stone dust laid and compacted.

Water does puddle on top during hard rain, but within a few hours after the rain, the pavers are dry.

 

[rieferman]

You should work REALLY closely with your contractor doing the paving to make sure your slopes all work to get the water to the drain.

In the past I have had some pretty poor results when the paving guys were left on their own. Too much slope with a low drain or uneven surface that leaves puddles.

I have had way better luck with concrete guys getting the slopes just right.

Sounds like you have some natural slope that will work to your advantage.

Cheers!

Totally agree. We picked this particular contractor because he has a history of doing a nice job, is local (his shop is at the edge of our neighborhood), and his family knows a lot of our friends and connections (e.g. his wife is a school teacher at the same school as one of our close friends).

That said, we spent a lot of time talking about drain placement etc. He'll be digging out about 4" of existing gravel material across the entire area so that he has enough room for base and top coat, so we'll be able to fine tune the natural slope as needed during that step.

I don't have a transit level, but I'll bet he does (and will follow up to ask him to bring it / use it).