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Garage drain for new house build

Posted on 4/21/26 at 3:11 pm
Posted by prestigeworldwide
Member since May 2018
432 posts
Posted on 4/21/26 at 3:11 pm
Looking for ideas on what type of drain would be best for my garage on a new house build. I was thinking of some type of square drain in the middle of the 2 bay opening so I can wash my vehicles.

Never had one before and always wanted one. All suggestions welcomed along with any pros/cons, size of drain pipe, etc.
Posted by Spelt it rong
Louisiana
Member since Oct 2012
10886 posts
Posted on 4/21/26 at 4:04 pm to
Your intention is to wash them inside your garage?

I like the idea of a garage drain regardless of the reason. frick it. Do it. 2" will suffice.
Posted by gumbo2176
Member since May 2018
19957 posts
Posted on 4/21/26 at 4:17 pm to
I'd be concerned about possible mold/mildew issues with humidity also being a factor if in La. with a damp floor following a car wash, especially if your garage floor is just a bare slab.

It would be better if it was epoxy coated with a non-skid finish so any water would not be absorbed into the slab.
Posted by cgrand
HAMMOND
Member since Oct 2009
48530 posts
Posted on 4/21/26 at 4:20 pm to
Do a prefabricated trench drain with traffic rated grate cover. You’ll need the frame and drain pipe on site when they form and pour the slab. Make sure you know what the invert of the drain should be relative to finished floor elevation of the slab and the invert of the receptor (so you can set the slope of the pipe)
Posted by Spankum
The Sip
Member since Jan 2007
61980 posts
Posted on 4/21/26 at 4:23 pm to
quote:

I'd be concerned about possible mold/mildew issues with humidity also being a factor if in La. with a damp floor following a car wash



Agreed…I also would think anywhere you wash cars would need traps to catch oil and also dirt so that wouldn’t go down the sewer. There may be some regulatory issues, too.
Posted by mtcheral
BR
Member since Oct 2008
2104 posts
Posted on 4/21/26 at 9:03 pm to
Why in the world do you want to wash your cars in the garage?
Posted by gumbo2176
Member since May 2018
19957 posts
Posted on 4/21/26 at 9:33 pm to
quote:


Why in the world do you want to wash your cars in the garage?



Watched too many of those car recovery shows where they take barn finds covered in filth and power wash, hand wash and then polish the turds to make them somewhat presentable.
Posted by Tree_Fall
Member since Mar 2021
1229 posts
Posted on 4/22/26 at 9:43 am to
Trench drain is a good idea. I'm thinking about putting one across my carport entrance when I have the driveway replaced. During very heavy rain I get some water backup. When your slab is poured include a moisture barrier everywhere including the garage. That will prevent damp slab problems if you coat the garage floor.
Posted by RaginCajunz
Member since Mar 2009
7167 posts
Posted on 4/22/26 at 9:56 am to
quote:

Trench drain is a good idea. I'm thinking about putting one across my carport entrance when I have the driveway replaced. During very heavy rain I get some water backup. When your slab is poured include a moisture barrier everywhere including the garage. That will prevent damp slab problems if you coat the garage floor.



Having added many catch-basins and 4" PVC runs to the rear ditch in Prairieville. I am a fan of drains. I dream of re-doing my driveway with trench drains across the garage door, carport, and random spots throughout. (Our driveway is fairly level with the yard, if not slightly below with the grass height. More drains are always better than less IMO.
Posted by Maillard
BTR
Member since Jul 2021
331 posts
Posted on 4/22/26 at 5:35 pm to
If you do it, add a trap primer line. Otherwise, when the p-trap dries out, you're going to start smelling sewage. Unless you're just going to run to a ditch. I would think that would violate many codes.
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