# Question about slope of garage slab foundation



## AndyGump

I am sure that your plans show that you have a min. 8" high x 6" wide conc. stem wall around the perimeter of the garage.

It should show that the stem wall is level all round.

Andy.


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## pttcc

The plan doesn't show that. It's monolithic slab of single pour with turned down edges.


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## AndyGump

But you are in California, a stem wall in a garage is prescriptive.

How did the engineer or Archy get by that one?

Could you post the plan or the detail showing the garage area?

Andy.


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## pttcc

Thanks Andy for the heads up. I will get it fixed!


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## AndyGump

BTW, on the slope issue:

*R309.1 Floor surface.* Garage floor surfaces shall be of _approved_ noncombustible material. 

The area of floor used for parking of automobiles or other vehicles shall be sloped to facilitate the movement of liquids to a drain or toward the main vehicle entry doorway. 

Andy.


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## jomama45

As Andy noted, a curb or stem wall formed and poured the same time as the slab is the correct way, code required or not.

As for pitch, 1" per 10 feet is extremely minimal, and a guarantee to hold water w/o an absolutely perfect installation. If you're DIY'ing this slab, you're going to have a hard time with the perfection part. Better to shoot for about 1" per 5'.


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## Willie T

And also be careful that you don't inadvertantly create a puddle trap of a low area all across the bottom of the pull-down door.


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## pttcc

I visited San Jose city hall this morning and talked to inspectors. According to them, monolithic slab is ok for garage foundation.


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## AndyGump

HI Pete, (I'll just call you Pete if you don't mind) a monolithic slab is fine yes.

But usually you will have a detail something like this to show the garage wall attachment to the foundation showing a stem wall.

Your plans do not have this?

This is just something I threw together to illustrate, your plans would be much more detailed than this.

Andy.


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## firehawkmph

jomama45 said:


> As for pitch, 1" per 10 feet is extremely minimal, and a guarantee to hold water w/o an absolutely perfect installation. If you're DIY'ing this slab, you're going to have a hard time with the perfection part. Better to shoot for about 1" per 5'.


Jomama,
So if he has a garage say 24' deep, your talking almost 5" of fall. That's seems like way too much. Maybe it's different in CA, but here in Ohio, 1 1/2" of pitch towards the door would be plenty. If you end up with puddles, then the guys didn't do a good job setting their grade pins. 
Mike Hawkins


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## concretemasonry

firehawk -

The slope and construction is a local need and preference and most codes allow for variations.

In many places, a true "floating slab" inside (and not connected to) the stem wall (concrete or block) is preferred. The floor slopes from a level at the the stem wall down to the desired location. Usually the stem wall is used as a raised curb. The slab can slope to the overhead door or to a central floor drain. A standard for decades.

If you have to deal with frost footings at the frost level it is much more practical and gives a garage that can be easily drained and kept clean, especially if it is an attached garage.

Dick


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## jomama45

firehawkmph said:


> Jomama,
> So if he has a garage say 24' deep, your talking almost 5" of fall. That's seems like way too much. Maybe it's different in CA, but here in Ohio, 1 1/2" of pitch towards the door would be plenty. If you end up with puddles, then the guys didn't do a good job setting their grade pins.
> Mike Hawkins


We almost always go with 3.5" (mostly because the height of a 2x4 is the simplest way to do it) on a standard depth garage. On a 24' depth, it's not uncommon to leave the back few feet level for ease in installing cabinets/workbench/shelves/etc... The pitch generally just needs to extend a little past the length of the vehicles parked in it. Here, the main concern is that ice/snow/rain that drip off of the vehicle finds it's way to the OH.

Have I gone flatter than 1" per 5'?? Certainly, but i do it for a living and I know our limits from pouring thousands of yards of concrete. More importantly, 95% of the time I'm the guy who goes back to saw joints, and I witness the flatness firsthand when snapping lines. From my experience, I wouldn't recommend that a DIY'er try to install a floor with as little as 1" in 10' unless they are willing to accept some puddles and standing water.


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## ddawg16

firehawkmph said:


> Jomama,
> So if he has a garage say 24' deep, your talking almost 5" of fall. That's seems like way too much. Maybe it's different in CA, but here in Ohio, 1 1/2" of pitch towards the door would be plenty. If you end up with puddles, then the guys didn't do a good job setting their grade pins.
> Mike Hawkins


Recheck your math....his spec was 1" per 10'....on a 24' garage, that would be about 2.5"....which is a lot. My garge is 25" and it slopes about 1"....and I don't have an issue getting water out.

pttc.....I would 'highly' suggest stem walls. Without them, your going to be cutting every single 2x4 stud a different length if you want you roof to be flat.

Click on the link in my signature for the Garage build....I went through it about 2 years ago.


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## joecaption

Personaly I'd never suggest a DIY try and pore there own slab, way to many ways for it to go wrong. As you guys know it's a one shot deal.
Without a stem wall behond what's been mentioned is the siding would be low and rot from splash back.
We also all know if the foundations messed up everything else above it's going to be messed up.


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## jomama45

ddawg16 said:


> Recheck your math....his spec was 1" per 10'....on a 24' garage, that would be about 2.5"....which is a lot. My garge is 25" and it slopes about 1"....and I don't have an issue getting water out.
> 
> pttc.....I would 'highly' suggest stem walls. Without them, your going to be cutting every single 2x4 stud a different length if you want you roof to be flat.
> 
> Click on the link in my signature for the Garage build....I went through it about 2 years ago.



Mike was referring to the minimum I suggested, not the min. mentioned by the OP, at least from what I can tell.

After looking at your garage build picture, it appears you could have really benifitted from a little additional pitch on the garage floor. The ramp to the garage must drop 5" in 3'................


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## ddawg16

jomama45 said:


> Mike was referring to the minimum I suggested, not the min. mentioned by the OP, at least from what I can tell.
> 
> After looking at your garage build picture, it appears you could have really benifitted from a little additional pitch on the garage floor. The ramp to the garage must drop 5" in 3'................


I think the pitch is fine....any more and I would find it uncomfortable to walk on....I do a lot of woodworking and I like a flat floor....but if water does get on it...it flows out fine.

As for the ramp into the garage....sore point....I was pissed at the contractor for making it so steep.....

Once I'm done with my 2-story addition...I'm going to replace the existing driveway with one without 'cracks'....and I'll saw cut the ramp and make it more gradual....


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## Willie T

We usually run 2 to 2.5 minimum on 20' slabs here.


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## firehawkmph

Interesting thread guys. I guess everybody does it a little different depending on where you are. Most of the attached garages around here get a drain in the middle that is tied into the sanitary in the basement. With the drain in the middle of a 24' x 24' garage, the guys usually pitch everything towards the drain in the middle with 1 1/2" being the fall. In my shop I have two areas. One is 28' x 56', the new addition onto that is 28' x 36' to make the building an ell shape. The original floor is poured flat with no drains. I didn't want any pitch in my shop area. When I do park in there, the snow melting off my van will leave a slight puddle around the wheels, most of the water hits the cut joints and finds its way out. The new addition we poured the floor flat except for the first 9' coming in from the doors. That area has a 3/4" pitch. I am planning on putting a twin post auto lift in there on one side and it calls for a flat floor. 
I definitely agree with the stem wall. Around here the bottom plate has to be at least 8" higher than grade.
Mike Hawkins


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## jomama45

ddawg16 said:


> I think the pitch is fine....any more and I would find it uncomfortable to walk on....I do a lot of woodworking and I like a flat floor....but if water does get on it...it flows out fine.
> 
> You "Think" it would be uncomfortable, but the reality is you wouldn't ever know the difference unless you could eyeball it next to the level curb. ANd, there's no correlation between a flat floor & a pitched floor. You can have both in conjunction, and they have no bearing on each other.
> 
> As for the ramp into the garage....sore point....I was pissed at the contractor for making it so steep.....
> 
> Other than replacing alot more of your driveway or putting more pitch on the slab, what other option did he really have?
> 
> Once I'm done with my 2-story addition...I'm going to replace the existing driveway with one without 'cracks'....and I'll saw cut the ramp and make it more gradual....


I think you're missing my main point here. You paid a professional to install the floor, with minimal pitch, and it still shed water to your satisfaction. For someone to attempt this with little to no experience, they're likely to have puddles or "duck ponds"......


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## jomama45

firehawkmph said:


> Interesting thread guys. I guess everybody does it a little different depending on where you are. Most of the attached garages around here get a drain in the middle that is tied into the sanitary in the basement. *With the drain in the middle of a 24' x 24' garage, the guys usually pitch everything towards the drain in the middle with 1 1/2" being the fall.* In my shop I have two areas. One is 28' x 56', the new addition onto that is 28' x 36' to make the building an ell shape. The original floor is poured flat with no drains. I didn't want any pitch in my shop area. When I do park in there, the snow melting off my van will leave a slight puddle around the wheels, most of the water hits the cut joints and finds its way out. The new addition we poured the floor flat except for the first 9' coming in from the doors. That area has a 3/4" pitch. I am planning on putting a twin post auto lift in there on one side and it calls for a flat floor.
> I definitely agree with the stem wall. Around here the bottom plate has to be at least 8" higher than grade.
> Mike Hawkins


Mike, if you consider that you're dropping that 1.5" in only half the distance (12' at most), you'll see that it's the equivalent to 3" in 24'. 3" really isn't that much different than the 3.5" I mentioned earlier...........

I certainly agree though that different regions have different requirements. Parts of the South that don't get freezing precip. dropping off of parked vehicles, or much rain, likely don't need the same amount of pitch. Also, dry concrete will absorb fairly large amounts of water more rapidly if the pitch isn't sufficient.


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## Ninjaframer

If I'm just trying to run water I use an 1/8 per foot as a min. slope. We do monolithic garages all the time here as long as they meet requirements for frost protection. I don't usually slope detached garages. I just slope the approach pad and drive way.


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## pttcc

Ninjaframer said:


> I don't usually slope detached garages. I just slope the approach pad and drive way.


Could you explain a little bit why you don't usually slope detached garages? Thanks!


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## Ninjaframer

It's not required. At least not in Utah. And it totally depends on intended use, if your not going to be hosing the floor down how is water going to get inside? Your door will have a weather seal that will prevent rain fall from getting in. Now if you need to be able to spray down the floor you should slope it but then you don't want a mono slab, you want stem walls with the floor set below there grade.


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## cmctyankee

AndyGump said:


> HI Pete, (I'll just call you Pete if you don't mind) a monolithic slab is fine yes.
> 
> But usually you will have a detail something like this to show the garage wall attachment to the foundation showing a stem wall.
> 
> Your plans do not have this?
> 
> This is just something I threw together to illustrate, your plans would be much more detailed than this.
> 
> Andy.


I hope this reaches Andy???
I saw your sketch in a post from 1/2012. It's exactly what I want for my garage.I haven't been able to find instructions, diagrams, pictures of the framing to construct to create the monolithic footer/slab/stemwall you described. Is there a web site, how to book, or whatever that I can obtain to see how this would be formed?


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## jomama45

cmctyankee said:


> I hope this reaches Andy???
> I saw your sketch in a post from 1/2012. It's exactly what I want for my garage.I haven't been able to find instructions, diagrams, pictures of the framing to construct to create the monolithic footer/slab/stemwall you described. Is there a web site, how to book, or whatever that I can obtain to see how this would be formed?


Pretty sure Andy draws for a living, I'm sure he could hook you up with whatever you need for a small fee..............:whistling2:


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## Canarywood1

cmctyankee said:


> I hope this reaches Andy???
> I saw your sketch in a post from 1/2012. It's exactly what I want for my garage.I haven't been able to find instructions, diagrams, pictures of the framing to construct to create the monolithic footer/slab/stemwall you described. Is there a web site, how to book, or whatever that I can obtain to see how this would be formed?


 

Don't know if this will help,but i like the wall to be 6/8 inches higher than the slab.

http://www.google.com/imgres?imgurl...AMEUqj0NpTlygHmjIHICw&ved=0CH4Q9QEwDA&dur=232


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## ddawg16

cmctyankee said:


> I hope this reaches Andy???
> I saw your sketch in a post from 1/2012. It's exactly what I want for my garage.I haven't been able to find instructions, diagrams, pictures of the framing to construct to create the monolithic footer/slab/stemwall you described. Is there a web site, how to book, or whatever that I can obtain to see how this would be formed?


Look at the pics in my Garage build link (in my signature).

Depending on where you are, you might need drawings from an architect.

Any decent concrete guy will know what to do.


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