Slope for garage floor

[central1ny]

So the excavator is coming tomorrow to start digging footings for the new garage. The mason was here today to stake out the garage but only got 3 stakes in the ground, and at the wrong locations at that. I am already scared by this mason who has been in business for > 20 years. But that's another story.

I need to know how to create the slope for the garage slab. I was under the impression that the correct thing to do would be to have the excavator slope the sub-base and then the mason would just pour the slab at a consistent thickness such that the slab is parallel to the sub-base. But the mason claims he always starts with a level base and then slopes the concrete to create the slope. I am having a 5.5” slab poured and the mason wants to slope from 5.5” thickness to 4” thickness. This just seems odd to me. What is normally done?

Also, how much slope should I have? The garage will be 24' wide x 40' deep. The rear 20 feet of the garage will be level for a workshop so the slope will run toward the door in the first 20'. I was thinking 1" of slope over 20'.

 

[Gary S]

I have no idea how the professionals do it because I did my own floor. I rented a Bobcat and excavated it at the slope I wanted the finished floor. Then I set my forms with the same slope as the dirtwork. My floor is then the same thickness across the garage. I'm happy with the results. Mine has 1" of slope every 4'.

Either way should work however if you don't mind different thicknesses from one end to the other.

 

[darkk]

Normal slope is 1/8" per foot sloped to the door opening. The excavator guy should slope the prepped area at 1/8" per foot. The concrete guy will follow the site work.

 

[holdover]

I poured mine about level, have a drain in an area that I might wash cars at some point and the pitch is very slight towards the drain for about 6' around it, no more than 1/8 or so. 1" in 4', which is about right for plumbing, seems like a lot, that would be 10" in 40', things might roll out of the garage without brake on..

 

[Gary S]

1" in 4', which is about right for plumbing, seems like a lot, that would be 10" in 40', things might roll out of the garage without brake on..

Yes, my vehicles will roll out of the garage if not in gear or the brake on, but I like it that way because in an emergency, one person can roll them out alone. My toolbox will also try to roll if not parked sideways along the slope.

 

[Ripped]

I am a contractor, and I'd suggest that you slope your (good quality) subgrade, and allow for 3.5-4" of good mpa concrete. Strong concrete will take bolts and anchors without breaking. Dig recesses for future equipment, such as lifts etc. It's only a few $ when pouring, even if you never install anything, It's hundreds of $, if you have to cut the concrete and do it later.

You can snap chalk lines, or drive in stakes (in the field) to indicate slope.

It depends on how much rain or snow that you get, but 2-3" of slope in 20' is good, if you have a placer who does not leave humps and valleys in the concrete.

Our current job, the architect has spec'd 6" of slope. IMHO, it's too much, especially if you're going to be working on vehicles (jacks jackstands etc)

Good luck

 

[ConCretin]

Normal slope is 1/8" per foot sloped to the door opening. The excavator guy should slope the prepped area at 1/8" per foot. The concrete guy will follow the site work.

X2. 1/4" will get most of the water out but is too steep and will cause issues with things you want level. 1/8" is marginal for moving water so be prepared for birdbaths. I'd pour it flat.

 

[bad_idea]

completly off topic, but related question: why does the garage floor need a slope? i understand for water to flow out, but what water?!? i have a 1 car attached that is 20 ft deep and has about 4-6" of slope from front to back. i would imagine washing the car in the garage would soak the drywall and lead to mold. i dont have a washer/dryer or hotwater heater in the garage. am i missing something? thanks for humoring my tangent.

 

[red]

Have you checked your Building Code? My garage floor was sloped for 1/8 per foot and the base was sloped as well. Will you install a vapor barrier? Today most masons place 1/2" of sand on top of the vapor barrier for the moisture from the concrete when it's drying.

 

[ConCretin]

completly off topic, but related question: why does the garage floor need a slope? i understand for water to flow out, but what water?!? i have a 1 car attached that is 20 ft deep and has about 4-6" of slope from front to back. i would imagine washing the car in the garage would soak the drywall and lead to mold. i dont have a washer/dryer or hotwater heater in the garage. am i missing something? thanks for humoring my tangent.

I'm kinda right there with ya. Never really got the point. I'd rather locate a drain or two if you need them than to try and move water the length of the garage.

 

[ansehnlich1]

completly off topic, but related question: why does the garage floor need a slope?

Here in PA when I roll in the garage with a truck that's just run through a half foot or more of snow she melts a good bit of water off into the garage. I always broom it out the next day, the right slope helps it drain out the front door.

I don't wash vehicles in the garage but I know many folks do just that.

 

[BADSIX]

I'm kinda right there with ya. Never really got the point. I'd rather locate a drain or two if you need them than to try and move water the length of the garage.

i'm kinda with ya to

 

[Licensed to kill]

If you live where there is snow, you need drainage like ansehnlich 1 said. However, if you live where you get snow AND it gets cold, sloping towards the door is not a good idea. The water will run to the door and the door will freeze to the floor. In this case, slope it t the center of the garage and put a drain. If you don't want to run plumbing for a drain, make a sump about 20"X30" and 2' deep with a grate (a piece of checker plate with a few holes drilled in it works fine) and just pump it out when it gets full.

 

[sfckiddo]

i wash mine out ocassionally have a strip around the walls like in a hosptal to keep water from them. 2 in over 30 ft. just built the form higher in the back and leveled the concrete with the form.

 

[70redbee]

Are you pouring a monolithic slab or using a stem wall? Where are you located,do you need frost protection? Need more info. to answer your questions.I have been buildind for 40 years and have never had an excavayor slope the ground for the slope, always level. After the excavator is done the concrete crew takes over prepping for slope,adding gravel,vapor barrier,wire and or rebar. The concrete crew is the one who has to level,square and make the finished floor correct. The prep work is the most important part. I like a level floor but many like sloped, local codes could determine what you have to do. If slope is required, I would keep it to 1/8" per foot at the most. There is nothing worse than working on something that is not level. Just my 2 penneys.

 

[darkk]

I poured mine about level, have a drain in an area that I might wash cars at some point and the pitch is very slight towards the drain for about 6' around it, no more than 1/8 or so. 1" in 4', which is about right for plumbing, seems like a lot, that would be 10" in 40', things might roll out of the garage without brake on..

hahahahaha! you flunked math right? 1/8" every foot for 40 ft is only 5" total. That's 1" every 8 ft. That is standard pitch.

 

[steel 35]

Mine is 2" total in 36' Enough I use a wheel chock and the water doesn't go uphill.

 

[Falcon67]

I told my guy I want it flat, square and level. Zero slope. I have no interest in chasing sockets out the door.

 

[holdover]

Darkk,
you flunked reading:
hahahahaha! you flunked math right? 1/8" every foot for 40 ft is only 5" total. That's 1" every 8 ft. That is standard pitch.

read it again, The pitch is only around the drain, not the floor length of the garage, except for this very small area in the 40 X 60 garage the floor is level

 

[central1ny]

Are you pouring a monolithic slab or using a stem wall? Where are you located,do you need frost protection? Need more info. to answer your questions.I have been buildind for 40 years and have never had an excavayor slope the ground for the slope, always level. After the excavator is done the concrete crew takes over prepping for slope,adding gravel,vapor barrier,wire and or rebar. The concrete crew is the one who has to level,square and make the finished floor correct. The prep work is the most important part. I like a level floor but many like sloped, local codes could determine what you have to do. If slope is required, I would keep it to 1/8" per foot at the most. There is nothing worse than working on something that is not level. Just my 2 penneys.

I have a block stem wall so the slab will be poured inside the stem wall. I am located in central NY where it gets very cold and 100's of inches of snow. The excavator is doing all prep work below the plastic.

 

[central1ny]

If you live where there is snow, you need drainage like ansehnlich 1 said. However, if you live where you get snow AND it gets cold, sloping towards the door is not a good idea. The water will run to the door and the door will freeze to the floor. In this case, slope it t the center of the garage and put a drain. If you don't want to run plumbing for a drain, make a sump about 20"X30" and 2' deep with a grate (a piece of checker plate with a few holes drilled in it works fine) and just pump it out when it gets full.

Does anyone here live where you get a ton of snow and still have a sloped garage floor?

 

[darkk]

Darkk,
you flunked reading:
hahahahaha! you flunked math right? 1/8" every foot for 40 ft is only 5" total. That's 1" every 8 ft. That is standard pitch.

read it again, The pitch is only around the drain, not the floor length of the garage, except for this very small area in the 40 X 60 garage the floor is level

OOOOPPs! stick foot in mouth! I concede sir, you are correct. You're not going to make me perform Seppuku for losing face are you?

 

[holdover]

no way, everything is cool, I have also put my fingers in gear before......

 

[steel 35]

Does anyone here live where you get a ton of snow and still have a sloped garage floor?

Is 600" a lot?

 

[mrobins297aaa]

I agree with "what water?"...... 1" in 4' that has to be a misprint, lets see in 64' ft that would be 16" of pitch.... omg!

I made my 36x64 flat, I do have a drain in the middle with a very small amount of slope in a 8' circle around the center of the drain

I don't like chasing sockets either.

for the record i think plumbing waste is pitched 1/8"/per ft

 

[Gary S]

I agree with "what water?"...... 1" in 4' that has to be a misprint, lets see in 64' ft that would be 16" of pitch.... omg!

Not a misprint. My garage has 12 inches of slope in the 48 foot length. I get lots of snow here and winter lasts a long time. My previous garages had no slope or minimal slope and they all ended up with water on the floor that eventually ends up as ice.
This garage drains itself when I pull in a snow and ice loaded vehicle and the ice melts on the floor. Now I don't have to clean the garage floor daily. I also have a 4" high ramp just outside the door so once the water reaches the door, it leaves the area on its own before freezing there.

 

[Motown 454]

If your worried about the water freezing to the door seal just hit it with some Armor All or silicone spray, the ice won't stick to it.

 

[darkk]

If your worried about the water freezing to the door seal just hit it with some Armor All or silicone spray, the ice won't stick to it.

Pam cooking spray works well on my snowblower....it's all we had at the moment. But it does work well for keeping ice and snow from sticking...

 

[duneslider]

Does anyone here live where you get a ton of snow and still have a sloped garage floor?

Around here it is code to have it sloped. We have had snow and single digit weather and I have never seen a garage door freeze shut. I am sure it could happen but I haven't seen it.

 

[ChargedUp!]

So how do you slope a garage with floor drains and a 2 post lift? Lift needs a level floor, right?

 

[ADSR]

So how do you slope a garage with floor drains and a 2 post lift? Lift needs a level floor, right?

Bingo. It's not that bad. You just need metal shims and shim the posts plumb.

 

[TOOL_MONGER]

... fwiw... code around here requires a sand/oil separator if you have a floor drain and it must go to the sanitary sewer, not always possible with a detached and/or un-heated garage...

 

[wedge40]

They just poured my garage and I have two drains about 6' from the doors. From the back toward the drains it slops to the drains and from the door to the drains it slops to the drains. This way I should never have standing or frozen water at the door opening.

Wedge

 

[ADSR]

... fwiw... code around here requires a sand/oil separator if you have a floor drain and it must go to the sanitary sewer, not always possible with a detached and/or un-heated garage...

Do you really go out and buy a permit? If i had to jump through hoops with a trap and such, i'd just pour it and call it existing.

 

[TOOL_MONGER]

Do you really go out and buy a permit? If i had to jump through hoops with a trap and such, i'd just pour it and call it existing.

you're the guy that pleads ignorance, and does what he wants...

With where I work, I have to follow the rules... and enforce them...

 

[ADSR]

you're the guy that pleads ignorance, and does what he wants...

With where I work, I have to follow the rules... and enforce them...

ahhh.. I guess you're a building inspector? I'm sure it's the same no matter where you live, the code book lacks a lot of common sense.

 

[dirttracker18]

Around here it is code to have it sloped. We have had snow and single digit weather and I have never seen a garage door freeze shut. I am sure it could happen but I haven't seen it.

We have double digit below zero temps and I have seen it happen. If you can get it not to freeze to the door seal then you get a hump of ice instead.

We never slope to the door around here as it is an issue. Better to be flat and broom it out later. I just put in a drain that goes out to the hill behind the shop. I parked in the garage last night and had all the snow melt off my truck. I would have had a pond in there otherwise

If the garage is not heated then you can just shovel the snow out the door.

 

[Bondo]

Does anyone here live where you get a ton of snow and still have a sloped garage floor?

Ayuh,.... I'm up here, on the other side of the snowbelt from ya,...

'round here, SoP to prep for a floatin' slab is to completely Level the foot print of the garage, at 4" to 6" below finish grade, dependin' on the thickness of the slab required for the loads anticipated..
4"s bein' standard for a car garage...
'n add a footer 'round the perimeter.. so's ya have a 1' thickness 'round the outside...
The footer runs 'bout 18" to 2' to the inside, 1' deep, with the floor level at the thickness ya want...
The sub-grade is never Ever pitched...

And, to answer the question in the quote, Yes,...
Either put a floor drain in it, 'n pitch to it, or pitch the whole slab to the door...
'n the pitch, ain't gotta be great, as anything not level, Drains....
1/4" in 10' is Plenty....

 

[KPSquared]

I have an inch on ten feet towards the trough drain that goes all the way across the shop a couple feet in front of my doors. Haven't parked in there yet but it should work.
Tons of snow melt here. . .

 

[NHBandit]

Well I guess I'll be the guy who goes against the grain and raises an issue that always rubs me wrong. Your concrete contractor has been doing this for over 20 years ? You hired him because he's an expert and you're not, correct ? Or did you just hire the cheapest guy you could find ? It makes a difference WHY you picked that particular guy. The first thing that comes to mind is the old sign I had in my automotive repair shop. You've all seen it. The one that makes reference to the labor rate being double if you ask questions & triple if you want to help. Don't get me wrong, I do understand the desire to make sure everything is done perfectly and you're talking about a considerable amount of money.. but... If I am hired to do a job based on the fact that I have MANY years of experience and have done this same job too many times to count, and if the customer is constantly pestering me with "don't ya think' & "maybe you should" ******** I am very likely to tell him to do it himself & walk away.. Just something to consider.