I am having an attached garage built. I had planned on having a drain in center that just goes to daylight (per code can't tie into the sewer line). That way when I come in with snow on car the water can just go down drain. It is big garage 27' 9'' deep and 24' wide, so may even wash cars in it. The general contractor wants to slope the slab so water runs out the front. Problem with that is that it creates issues with the entranceway into house and getting the rise and run of steps correct. I think he was talking about 8" (1/4" per foot would be about 7" in my 27' 9" garage) I would like to hear the pros and cons of having flat slab with drain vs sloped slab or combination.

 

If I had the choice, I would go for the drain every time.

 

If you are having a garage with concrete block stem walls and a floating concrete slab about 8" below the top of the block, you can get away with less slope since you cane easily wash/sweep it out without rotting the wood since the wood will be high and dry.

If you bring in snow, you will also drop ice and sand that you will have to get rid of. Your drain will have to slope enough to keep reasonably clean unless you want to flush it periodically.

Much depends on the amount of snow/ice/sand/slop you have in your area.

 

Oh crap! I just somehow lost a whole page of text I had responded to your topic with. Here goes again.

By all means, pitch your nice new garage floor to one of those nice new space age plastic garage floor sumps and run a pipe to daylight if it's practical. If it is not practical to go to daylight and works with your local codes and inspectors at least run the 4" drain pipe from the sump ouitside the garage and well away from the foundation pitching 1/8" per foot to a mini drain field of 10 to 30 feet of level perforated pipe. You can't wash cars or let the hose run forever through this drain but for strictly water dripping off a car this system is more than adequate.

The floor sumps I'm talking about are designed to have a big catch for road gravel and debris to drop into and the 4" drain pipe is above the well so water escapes the gravel debris. They have a nice 10 1/2" square space age plastic grill you can drive right over that rests flush with the floor that is poured sloping to it. Just after finishing a garage floor we always saw a slight relilef cut (3/8"). This cut follows the line we snapped through the center of these sumps dividing the garage floor in quarters. When the floor checks, chances are pretty good the crack goes right down the scores we provided to the drain hole so it won't show.

Now you have described your garage as basically 28 X 24.
I shall assume you might drive through one of two nine foot garage doors in the 24' wall. The garage sump belongs in the middle of your floor and needs to set below outside floor level of by no more than 2". for that 24' wall (with a sump in the middle) that equates to 1/6 " per foot. As for the long wall, your car only needs to be driven into that garage a maximum of 20-22'. (probably less) The floor needs only be pitched beneath the car leaving the back 6-8' of surface of the garage floor poured flat. Center the drain beneath the car and your taking up say 20 or 22' of the 28' length and the floor pitches perhaps 10 or 11' either side of the drain. This time you are more than 1/6" of drop per foot. What we are trying to do is just keep the water beneath the car and the reason follows.

If you pour that floor flat, some of that salt brine and water coming off that dripping wet car loaded with melting snow or rain water goes to the outside wall. Garage walls are usually collection points for shovels and lawn mowers and boxes and foot traffic none of which survive well in salt brine or water for that matter.

Now that front lip of the floor that sticks out beyond the garage door needs some hand work when the floor is poured. We don't want that pitching back to a floor drain inside. A good concrete man will take and cut that level slightly below the form as the concrete is poured. He wants to see to it that water pitches away from the garage door at that vulnerable point. You don't need the floor approach lip outside the doors pitching to a sump or water will be running into your drain in garage from outside when it rains. We are speaking of that area of floor that is just outside the garage doors. With this slight difference your floor is basically only a 1/2" or so less that outside floor grade so you have plenty of help for that step grade.

.02 worth for free, I'm finally done.

bs5

 

thanks all. I live in Baltimore, so not really large amounts to deal with. I know the slab will not be in contact with any wood. As far as these sumps, can you tell me some names that I can look up on web site? Are they available at HD, Lowe's ? I lost you a little in your description. Let me clarify my dimensions. you enter on the 24' side and it is 28' deep. I understand about front of slab level, say 10', leaving the rear 18' for the car. so of that 18', the drain will be in the center of that meaning there will be 9' between doors and sump and 9' from sump to the area where slab is flat. So you want both of these 9' areas to slope to the sump. What is the pitch to be? And it will be centered L to R in the 24' wide garage, so there is 12' to left of drain and 12' to right of drain. What is the slope here to be? are you able to draw something and scan it in particularly showing the front apron area?

Thanks
Bill

 

Yes if it was my garare then there will be an drain install

 

http://www.ndspro.com/cms/index.php/...-&-GRATES.html

would these be what you are talking about?

Bill

 

or how about this channel drain --two of them running long ways front to back under each car? but it says you need expansion joints running parallel to channel 4" from it on each side which would seem awkward.



http://www.ndspro.com/cms/index.php/...EL-DRAINS.html

 

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The drain box you have linked is very similar to the floor sumps we used to use. The ones I used were a bit simpler in design however. Instead of that double snout on the side of that thing you linked a plastic ring sealed the perimeter of a 4" pipe as it fitted through a larger hole cast in the side of the box. We bought them at our local "Do-it" Hardware store that also happened to be a building centere or at those "Plumbery" stores. These stores are usually run by larger plumbing contractors and seem to sell lots of plumbing pieces to the public and other tradesmen. They are really heavy duty and we always set them in a half wb load of concrete or even mortar a day or so so they maintained their level and plumb position prior to the poor. We filled the sump with sand after temporarily plugging the 4" drain pipe and usually left the top or grille right off so it did not get covered with concrete when we poured the floor. After the floor pour a flatwork guy has to get out there with toe boards and a bucket and rag and clean that sump up digging the excess concrete out of the sand filled opening before it dried. As he exits on the fresh and fairly soft concrete floor he can take a couple of nice arcs around the drain to clean up the finish.

I think we both had our descriptions adequate for the floor dimensions and floor plan and with a 24' wall with two nine foot doors you will have no extra room so the doors get centered. The floor drain does indeed get placed in about 9 or 10' in and as it works out will be in lline with your short wall section between your doors. The floor beneath each car slopes the opposite direction but to a common and single drain. For a pitched garage floor the size you are building the floor can be screeded in two 12' pulls over three screed pipes the center one sloping to drain and outside pipes remaining level. The screed pipes slid over the tops of the stakes and the void filled as you work the poured concrete back out to garage doors and forms across doors.

Now, your concrete guy is going to have his own way of doing things so I hope you don't insist he has to do it any other way. However you asked and we made it work for us. First we established the floor grade and snapped that on the side of the block foundation. now we stretched a string stake to stake through the center of the drain and attached a tight mason's line. What ever the top of he floor was shot with the transit, and in your case we would add two inches to that measurement and set the top of the drain box at that grade. This means we just pitched the floor by 2" from outside to center and that is 12' to outside of foundation as we are running parallel to the plane of your garage floor here. Floor sump 12' (less thickness of block) wall to center of floor drain and 2" below os floor grade. That for all practical purposes happens to be 1/6"/per foot. Magically, we use three screed pipes and only one follows the pitch to the drain. Outside pipes are flat and slide across the tops of 1X4" stakes shot to grade with a transit or laser level (plus thickness of outside measurement 1 1/2" iron pipe screeeds) The stakes make three rows and the centere string we talked about to weight to top of drain and then drive 1X4" stakes centered beneath the string and thickness of screed pipe below grade. The string through the center of sump gets weighted to the level of the sump and following placement of stakes and screed pipes you get a floor pitched to a drain So I hope you are starting to understand the method. I can't tell you all the secrets of the trade but basically given a system that I poured many a floor utilizing over the years. To each his own but it worked for me. Floor slopes need not cause water to jet too the drain. but a pitch like this for a floor leaves those perimeters we talked about high and dry and a man does not have to slip down a slippery slope as he walks across this floor. Good luck.

bs5

 

thanks for all the info. since this is 2 car garage, the middle area will likely end up with junk, like someone previously mentioned about the sides of the garage. What do you think of having two of these basins, each one centered under a car, so that the center stays dry?

 

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You asked what I think of a separate drain under each car bay. Quite honestly I would say that it's a moot point. For a 24' wide garage width that is going to have two 9' garage
doors that only leaves you with less than two feet spacing between the door opening and the two outside walls and two feet between the garage doors. How do you open your car doors without taking out junior's Schwinn bicycle. No room left in the middle for any storage. That's just the way it is. And it gets worse, these two nine foot doors get placed in less than a 24' wall because we are probably centering them inside the two opposing block or poured walls. Why make your flatwork crew have to screw around with setting up a much more complicated floor with an extra drain when it does nothing for you.

That is the way I see it. Maybe someone out there disagrees with me.



bs5

 

Well, first let me say that I only *wish* I could have a garage as big as what you're planning to build. That would be nice. Unfortunately the cars would slowly get elbowed out by my saws and tools and such.

My parent's garage is level. They bring snow in and it drips on the floor but rarely makes a puddle bigger than the tire. And then it evaporates. They sweep it once a year whether it needs it or not. They have no floor drain and never needed one. I would just imagine a floor drain being great if you were going to wash cars, but I really imagine that a guy would do that out in the driveway. I'd tend to use the floor drain as a giant dustpan and then I'd cuss when it came time to clean it out. heh heh!

They really like their 18' garage door that I put in for them. We replaced the header with a laminated beam in their gable end so it should never sag. They like it much better than their old double doors and that stupid post in the middle.

Oh- the other reason a level garage floor is nice is so that you can set old cabinets on the sidewalls and have a nice workbench. But I have seen a lot of new houses with the cement stem wall and floating floor inside with about 1/4" per ft of slope. I just don't see the point. How often do you hose your garage out? I wouldn't like a slope on the floor because nothing you put on the floor would sit level and plumb. I think that would drive me bananas.