Concrete Slope

[knightp25]

Hi, I am building a 17 x 22 garage

I currently started building the form for the concrete, for a 22' foot run I have the slope so far set at 3/4' from back to front.

My question is should I adjust higher, my drain will be in the front of the garage right outside of it. Thanks

 

[James-W]

What are planning on doing in the garage? Will you be using it as a garage (park cars inside) or will it be a workshop? If it is going to be a workshop I would make it flat instead of having a slope.

 

[Justanoldguy]

Extremely rare for garage floors to have any slope here in NZ.
But, I guess, we don't have a snow problem here either.

 

[knightp25]

I live in PA so we do get snow and rain, plan on using the garage as a regular workshop, storage, park cars.

I though it would be best for some slope in case water gets in, but I didn't want the slope crazy, to where my tool boxes would roll out of it.

 

[K'ledgeBldr]

The IRC has one of the most vague descriptions for this particular standard. The key word is "slope"- and that's it. There are no "numbers" associated with this requirement.

I've had AHJ's that did have concise directives for this standard- it was usually 1/8" per 12".

There is one directive that does give numbers-
ACI 362 recommends a minimum of 1.5% slope in any direction, with 2% being preferred for garages.

 

[larry_g]

does 3/4' = 9" If so a bit steep but not outrageous for parking in a snow zone. Me I have a level floor because it is more shop than garage.

lg
no neat sig line

 

[ssdave]

I've always used the rule that concrete, well finished, will drain water without ponding at 1/8" per foot. So, for a 22' floor, you'd need about 3 inches of drop across the 22 foot dimension. That's about 2% slope. If your finisher isn't real good, I'd double that to 1/4" per foot, for a total of about 5 inches in 22 feet.

 

[readhead]

I'm a little confused. Are you forming a slope into the entire slab? The edge of the slab should be level. If not you will be cutting every stud.

 

[James-W]

I'm a little confused. Are you forming a slope into the entire slab? The edge of the slab should be level. If not you will be cutting every stud.

If he has a stem wall then the walls should be straight and level and only the floor will be sloped. But you are right, he wasn't real clear on that.

 

[DougWil]

I have a raised stemwall in my shop and put in a 1/4" per ft slope on the floating slab.
Great for washing out the shop. Pain rolling around heavy things uphill on a floor jack or the gantry crane that always wants to head for the door.

 

[ItsNemo]

1% slope is ideal...anything more and a vehicle in neutral/off brakes will roll on its own.

 

[WVBrady]

If you just tilt the floor, any water that does not go out the door will run into the wall.

 

[Jackfre]

I built mine flat. For leveling tables and such it is much easier when doing projects. I have a 3' squeegee to take the little water the place ships. I put a 3/4" step at the door so water does not flow into the garage and the apron is at 1/4" per ft away. Good so far. It doesn't have to be sloped. My inspector asked about the grade and I told him it was "just fine". No problem.

 

[ct03911]

Mine is 27 1/2 foot deep and over 3" slope.
My cars don't roll and my tool boxes sure don't.
I haven't washed in there yet to see if it made any real difference in runoff for car washing, which was the plan.
I can't see how a little more slope would hurt.

 

[Fixin'Stuff]

A friend of mine built his to slope slightly towards the drain he installed in the center of the floor. This let snow melt and not have the runoff freeze the door to the slab and also let him wash his cars indoors.

 

[BillK]

My 24 x 24 detached garage is flat. I played heck convincing the concrete guys to do it that way years ago but am glad I did. If you are going to use it as a workshop then you definitely want it flat and level.

The attached garage on the house is sloped about 2 1/2 inches from front to back and it is a pain. Putting in any type of floor mounted work bench or cabinet along the sloped wall requires shimming.

 

[knightp25]

Thanks for all the replies, Yes will be sloping the entire floor from from to back, was also planning on putting up a metal building

 

[maxpower_hd]

My garage is used as a workshop and is sloped too. I also work on cars and motorcycles in it and wash them. So it is nice to have the water run out. I also pressure wash the floor from time to time. I don't have ANY issues with motorcycle jacks, cars, tool boxes or anything else rolling out and I have a polished floor. I did have to put shims under the bench when I built it which is 16 feet long but I certainly didn't have any difficulty doing it.

I currently have a Toyota truck in there on wheel dollies and it doesn't roll out unless I push it and get it going. I do have shims in front of the wheels in case someone does push on it unintentionally but by no means do I have things rolling around the shop uncontrollably.

 

[readhead]

Need more info. What type of metal building. Red iron or carport style? Different footing and bolt requirements for each style. Either one will require a flat surface to be erected on. Some slope can be formed into the slab and retain a level edge or a floor drain could be placed in the slab. Are you clear on your foundation requirements?

 

[lakeroadster]

Once you go flat, you'll never go back.

Once you go flat, you'll never go back.

Local building codes may dictate if it indeed needs slope. Here, if the garage is attached to the home it has to be sloped.

If it is a free standing building and not attached, no slope is required.

My last building had 4" of slope and was 28' deep. It was a nuisance. Cabinets along the wall needed every leg a different length, hard to keep things level that were being built on the floor, and cars easily pushed out the door, not easy at all pushing into the door.

My current pole barn we poured the slab about a month ago, and it is flat.

 

[wssix99]

I live in PA so we do get snow and rain, plan on using the garage as a regular workshop, storage, park cars.

I though it would be best for some slope in case water gets in, but I didn't want the slope crazy, to where my tool boxes would roll out of it.

The slope required by code is required so heavier-than-air gas fumes flow to the door and out of the garage, where they are explosive. As mentioned above, a 1/8" to 1/4" per foot slope will do this for you.

1/8" per foot is just fine for a "flat" work surface. I can roll a 600 lb cart around on my 1/8" per foot floor with no noticeable effort from the slope.

If water flow and snow melt is your concern, I can tell you from experience that 1/8" foot is not going to cut it... It's not aggressive enough. The variability in the surface finish of the floor causes some slight pooling/puddling and it leaves salt flats and dirt spots that need to be periodically dealt with. If you deal with a lot of snow melt and want to flow that out of a heated garage, then I'd go with a more aggressive slope.

 

[jives]

This issue has come up here several times. I urge you to search for the comments. Our garage (32 x 42) was built with no slope. Quite on purpose. Yes, the cars bring in slush, snow and drip from rain. Even with a slope I would squeegee out the slush with a 3' curved squeegee. Works great.

 

[K'ledgeBldr]

The slope required by code is required so heavier-than-air gas fumes flow to the door and out of the garage, where they are explosive.

Well, that's a new one.
Maybe you should read IRC R309.1
As I previously mentioned, there are no "numbers" attached to this code- the only reference to "slope" is the word itself- it's "to facilitate the movement of "liquids".

*aren't gas fumes just as explosive outdoors as they are indoors?

 

[78Bird]

Not really, no they aren't. Outside they dissipate, and it's hard to get to the concentration needed to ignite. remember any fuel needs the right fuel/O2 ratio to burn or explode.

Inside, MUCH easier for it to build up to a kaboom.

 

[wssix99]

Well, that's a new one.
Maybe you should read IRC R309.1
As I previously mentioned, there are no "numbers" attached to this code- the only reference to "slope" is the word itself- it's "to facilitate the movement of "liquids".

*aren't gas fumes just as explosive outdoors as they are indoors?

That's a handy way to kill two birds with one stone. If liquids flow, the gasses in question will, also. Many municipalities will not care so much about the fluids. The gasses are the more pressing safety issue. Other code requirements for the "gas curb" (so the gasses don't flow in the house) and for interior garage drains to drain to free air are related to the same phenomena.

The IRC is cute and I know that its widely used, but it certainly doesn't cover all the bases, which is one reason why major cities don't use it.

If you google "Garage Explosion" or "Sewer Explosion", there are lots of examples of how these environments are more hazardous than fumes in outside air. Anything that constrains the movement of vapors and keeps them concentrated is a problem. Here's a great example of a boat:

(A garage can be much worse.)