Channel / floor drain - how much?

[thoraxe]

I am doing a large garage build and would like to be able to wash cars in the building. You can find out more in my build thread:

https://www.garagejournal.com/forum/showthread.php?t=325666

Here's the tentative floor plan (move the lift to the left in your mind, but basically doesn't matter):


I want to put drains opposite the lift so that I can pull a car in the door, wash it, and then back it out. Yes, I know I have to look into my local codes to see what requirements there are for traps, separators, whatever. I am on septic but was hoping to just have the drain go into the yard -- after all, if I wash a car in the driveway, the water just goes into the yard anyway.

That being said, my question is more about how MUCH drain I need. I am in Atlanta, no snow, just sometimes rain. Car washing would be the most water accumulation. I have an E350 van that I would need a ladder to wash, but it probably wouldn't be more wet than washing a regular car.

I'm looking at these:
https://www.lowes.com/pd/NDS-40-in-L-x-5-in-W-Channel-Drain-Kit/50373212

It says cars / light trucks, so I assume it would also work with an enclosed trailer. I probably need to look at the NDS website to find the specific maximum weight that can roll across these. But, I digress.

How long of a drain should I do? The van is 80" wide. An enclosed trailer is ~110" wide. I assume I want at least as wide as the thing being washed, or if the floor is sloped a little does it not matter? I'm also okay using a squeegee if need be. It's almost 10' of drain to be wider than an enclosed trailer....

Thanks!

 

[ConCretin]

I prefer to locate floor drains under each vehicle parking area. Based on a 10' by 20' footprint, setting the drain 1 1/4" low results in a functional pitch to the drain of 1/8" per foot the long way and 1/4" pitch across the vehicle. This is adequate pitch to eliminate most bird baths and promote drainage.

Locating the drain under the vehicle allows the surrounding areas too be level, which avoids issues with tool boxes, work benches, etc. I wouldn't bother with trench drains. A simple round grate works just fine.

 

[Chris705]

I would agree that a simple round floor drain would suffice and the amount of water used to wash a car doesn’t require a trench drain ( but you may want to consider a drain with removable grate and internal catch basket to contain debris that may get washed down the drain). I would stress/urge you have a conversation with your mason to make sure they understand the extent of the sloped floor area. All too often when placing a large floor like yours the contractor will lessen the area of sloped floor and increase the slope to a smaller area. I wash my vehicles in my garage and often have to squeegee and each time I do I curse my mason cause they failed to get the extents of the area I requested be sloped.

LLWillysfan would you comment on how to converse with a mason to get this sloped area installed correctly and would there be any merit to pour the sloped area as a separate pour so the mason can focus on that task specifically?

Thorax - best success with your pour and the rest of your garage build!
Regarding an oil/sand separator, you won’t need a very large one, Schier (and others) make some small units you can locate just as your plumbing exits your footprint.

 

[joes169]

First of all, you have the trench drain orientated 90 degrees off from where it should be. THe 3' side slope is going to be extreme, or the 12' long slope is going to be too flat to shed water.

Second, trench drains work best in long rectangles, round drains work best in relatively square areas. The length of a trench drain is generally determined by the difference of the length vs. width of the area you're trying to drain. For example, in a 12' x 20' area, itis ideal to have about 8' of trench drain so that the pitch from all four sides is equivalent.

Third, 1/8"per foot pitch is a little light IMPO. Not to split hairs, but I like to set them closer to 1/6" to 1/7"per foot to ensure good water flow. In a perfect world, 1/8"per foot is plenty,but until they we can eliminate the human error factor out of concrete placement, I prefer a little more pitch........

 

[ConCretin]

LLWillysfan would you comment on how to converse with a mason to get this sloped area installed correctly and would there be any merit to pour the sloped area as a separate pour so the mason can focus on that task specifically?

The first step is obviously to reflect the desired floor pitch in the sub grade and secondly to set the drain to the desired elevation. In addition I like to stake out the limits of the sloped areas with something the finisher can easily pull out one the floor is screeded. At this point all the finisher needs to do is connect the dots.

Third, 1/8"per foot pitch is a little light IMPO. Not to split hairs, but I like to set them closer to 1/6" to 1/7"per foot to ensure good water flow. In a perfect world, 1/8"per foot is plenty,but until they we can eliminate the human error factor out of concrete placement, I prefer a little more pitch........

I don't necessarily disagree. 1/4' per foot is the generally the minimum to dependably move water and prevent birdbaths but when placing a drain in the center of a 10' x 20' area, the pitch the long direction is doubled the short way. This can result in a pretty abrupt drop in the middle of a garage. I'm sure the pitch you suggest would be fine but I did mine with 1/8" and I don't get any puddles.

 

[Neighbor]

My garage is similar size to yours. 32x48 I installed a trench drain running lengthwise in the center. All the concrete is sloped to the drain. I don't remember for certain but I think all tolled cost about $2,000

 

[mike93lx]

How often are you washing your cars? Maybe just pitch the slab to the door and push any standing water out with a squeegee? That way you can maintain a relatively flat floor

 

[thoraxe]

The first step is obviously to reflect the desired floor pitch in the sub grade and secondly to set the drain to the desired elevation. In addition I like to stake out the limits of the sloped areas with something the finisher can easily pull out one the floor is screeded. At this point all the finisher needs to do is connect the dots.



I don't necessarily disagree. 1/4' per foot is the generally the minimum to dependably move water and prevent birdbaths but when placing a drain in the center of a 10' x 20' area, the pitch the long direction is doubled the short way. This can result in a pretty abrupt drop in the middle of a garage. I'm sure the pitch you suggest would be fine but I did mine with 1/8" and I don't get any puddles.

Thanks LLWillysfan!

It sounds like if I just want to drain one car area, a single round drain would suffice (one round drain for a 10x20 parking area)?

Looking at Lowes' product selection here, I don't think the plastic round grates are rated to be driven over. I'm also not sure if I would need a catch basin, or if I could just have a round grate over a hole in the concrete that then exits out to the side.

Chris705 - this appears to be the smallest / cheapest thing from Schier:
https://schierproducts.com/gb1/

Is this all I would need? It's still $500!

 

[thoraxe]

I got some confirmation that daylight drain for the garage floor will be OK.

So now the only question is what kind of actual physical drain do I put in the floor in the 10x20 area, and what should the slope be?

It sounds like I need ~1/8" - 1/4" of slope per foot to avoid pooling/puddling, but I don't wash cars often and I don't get snow, so I'd be OK with squeegee-ing after a car wash.

 

[Chris705]

Do two round drains if you want to stick to 1/4” per foot... or use one drain and have different slopes, the key from my perspective is to be sure your mason is on board and understands what you want. I like LLWillysfan thought on putting in the grade stakes (metal stakes available at the BB stores used to hold form boards in place. Buy four of them and have the extents of the sloped area set to your finish floor elevation. They then place the concrete inside this area sloped to the drain whose elevation is set according to the side slopes being at 1/4” and the top/bottom triangles being at 1/8” per foot this is when one drain is used....

I’d use a 4” round floor drain... something like a Watts or Zurn....I think you would still want to put a 4” pipe trap in to be sure to keep insects and other crawling insects out of the drain....hope you have enough fall in elevation to accommodate that and still drain to daylight.

 

[joes169]

I got some confirmation that daylight drain for the garage floor will be OK.

So now the only question is what kind of actual physical drain do I put in the floor in the 10x20 area, and what should the slope be?

It sounds like I need ~1/8" - 1/4" of slope per foot to avoid pooling/puddling, but I don't wash cars often and I don't get snow, so I'd be OK with squeegee-ing after a car wash.

With a 2:1 ratio, I'd recommend about 8-10'of trench drain, running down the center of the long direction, so water is only running 5' from all sides and about 7-8' on the diagonals. This would keep the drain completely out of any tire traffic as well.

If you really want to use a single round drain, these are the industry standard around these parts:

https://www.menards.com/main/plumbi...ity-floor-drain/860-3pspk/p-1444442711385.htm