Help! Setting slope for slab?

[cdnc]

Gents - I've recently had a new 30x40 shop built. The footings and foundation wall were poured, but the slab will be poured after the frost is out of the foundation. We back filled with limestone screening. The stub wall inside will be 8", the slab 5" and 2" of foam insulation. When back filling we brought the screening up to about 15" below the top of the wall (8+5+2).

My question is how to set the right slope for the slab. The building inspector suggested 2% slope and I'm assuming that has to be managed by grading the limestone screening (vs having the slab thicker at one end and 'tapering' to 5")?

Do I snap a chalk line along the wall starting at the 'high point' of 15" below the top of the wall and then do final grading of the screenings to something like 20+" below the top of the wall (8+5+2+Slope of 5"-10")?

My plan is to have a more gradual slope of something like 1% over the first 20' where more of a shop will be and a potential lift and then increase slope to something like 1.5% towards the doors and trench drains where I will be parking tractor, trucks, etc for snow melt.

How do I make sure I am level across the 30' - laser, line, board,...?

Am I thinking of this the right way? I'm assuming that the concrete contractor will just pour on the grade and can't do much to set the slope. Help?!

Thanks CDNC

 

[Armorpoxy]

In our experience most competent concrete contractors can lay concrete to a slope as directed. Just tell them what you want, say the 1% and they should be able to comply.

 

[cdnc]

In our experience most competent concrete contractors can lay concrete to a slope as directed. Just tell them what you want, say the 1% and they should be able to comply.

I'm trying to get my head around that - so do they start with a 10" slab and work down to 5" for a 1% slope or 15" down to 5" for a 2% slope? That would more than eliminate the stub wall exposure at the "high" end? It seems like it would also use a ton of extra concrete?

Cheers Hugh

 

[schultzy]

Slab thickness should stay the same throughout. I believe you adjust for slope with your screenings.

 

[mitusa]

I'm not sure how you're figuring your slope but on a forty foot floor, the drop wouldn't be much. And I would think you would do it with your screenings......

 

[cdnc]

I'm not sure how you're figuring your slope but on a forty foot floor, the drop wouldn't be much. And I would think you would do it with your screenings......

That's what I thought as well. The slope would be 5" for 1% and ~9+" for 2% so it's fairly substantial.

 

[mitusa]

Bump for more opinions.....

I think a 1% slope is more than what I would want. Most of the barns around here are poured level with maybe a little slope at the doors.

Hopefully, others will chime in with their opinions.....

 

[Elginz]

5" over 40 feet seems like a lot to me.

 

[mmavet]

Your builder should have the front overhead door already set for you. If your using a 8' door just measure down from your header 8' , if 10' door measure down 10' and make a mark on the wall. Measure up from your mark to the top of the wall. That measurement gets transferred to your outside walls and chalk your a line across the front wall. Line should be level from side to side.
From there check your local building code for minimum fall on garage floor, ours is 1 1/4" per 10 feet of length for floors with out a drain. 40' deep would be 5" minimum. Go to your back wall and add 5" to the measurement that you had across the front wall. you should now be able to chalk the back wall. From there you should be able to connect the back and front lines by chalking your side walls. 40' is almost to much to try and chalk so find your 20' or middle of side walls and just take the amount of fall from back to front and divide by 2 and make a height mark in the middle of your side walls. Just grade your floor accordingly.

Gents - I've recently had a new 30x40 shop built. The footings and foundation wall were poured, but the slab will be poured after the frost is out of the foundation. We back filled with limestone screening. The stub wall inside will be 8", the slab 5" and 2" of foam insulation. When back filling we brought the screening up to about 15" below the top of the wall (8+5+2).

My question is how to set the right slope for the slab. The building inspector suggested 2% slope and I'm assuming that has to be managed by grading the limestone screening (vs having the slab thicker at one end and 'tapering' to 5")?

Do I snap a chalk line along the wall starting at the 'high point' of 15" below the top of the wall and then do final grading of the screenings to something like 20+" below the top of the wall (8+5+2+Slope of 5"-10")?

My plan is to have a more gradual slope of something like 1% over the first 20' where more of a shop will be and a potential lift and then increase slope to something like 1.5% towards the doors and trench drains where I will be parking tractor, trucks, etc for snow melt.

How do I make sure I am level across the 30' - laser, line, board,...?

Am I thinking of this the right way? I'm assuming that the concrete contractor will just pour on the grade and can't do much to set the slope. Help?!

Thanks CDNC

 

[coldh2o]

I went about 2%, 8" over 40'. Hardly noticeable except when building benches along the long wall. Slope the gravel.

 

[cdnc]

Your builder should have the front overhead door already set for you. If your using a 8' door just measure down from your header 8' , if 10' door measure down 10' and make a mark on the wall. Measure up from your mark to the top of the wall. That measurement gets transferred to your outside walls and chalk your a line across the front wall. Line should be level from side to side.
From there check your local building code for minimum fall on garage floor, ours is 1 1/4" per 10 feet of length for floors with out a drain. 40' deep would be 5" minimum. Go to your back wall and add 5" to the measurement that you had across the front wall. you should now be able to chalk the back wall. From there you should be able to connect the back and front lines by chalking your side walls. 40' is almost to much to try and chalk so find your 20' or middle of side walls and just take the amount of fall from back to front and divide by 2 and make a height mark in the middle of your side walls. Just grade your floor accordingly.

Thanks for the guidance. I'll go have a look tomorrow and think about this as I think I have to be looking at the building to understand. The doors are 10 x 10 and I believe the opening is cut low to allow for the slab to be poured over the cut-out.

CDNC

 

[cdnc]

I went about 2%, 8" over 40'. Hardly noticeable except when building benches along the long wall. Slope the gravel.

Good to know. The inspector suggested 2% as well. I think I'll try 1% at the back and then 1.5 - 2% at the front.

 

[machsnell]

We pour concrete and I did my garage floor with a .7 percent slope. 2 percent is what is done for roads and sidewalks outdoors to shed water. 2 percent is a lot and noticable to a trained eye easy.

Unless you are washing cars in there go as slight as possible.



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[zporta]

I would stick to 1% which is about 1/8" of fall per foot. That is what garages in the area are allowed that are MD inspection stations.

 

[pstnbly]

1% or 5" is plenty.

 

[cdnc]

I'm wondering less about the slope vs how to set and measure. I spent a bunch of time looking at the cutouts and I'm worried that the way things are cut I can't actually put a slope inside. Per MMAVET's comment I looked that the cutouts

The cutouts is effectively 10' 5" from the header. The door is 10' and the slab is 5" (over pour on top of the cutouts in the foundation wall) to close that gap. The problem is that the man door and garage door at the other end of the building have the same cutout....so I do t think I can actually slope the floor the required 5" - 10".

Am I missing something?

CDNC

 

[cdnc]

Thought I would post a pic to clarify. From the top of the foundation wall to the bottom of the cutouts is 12". From the header of the door to the bottom of the cutouts is 10' 5". The slab is 5". The distance from the cutouts to the garage trim piece is 5".

Thoughts?

 

[On-Wheel]

5" over 40 feet seems like a lot to me.

A car in neutral would never stay still.Those #'s must be for sewer lines.

 

[On-Wheel]

Run a chalk line on walls .Use a transit to shoot for grate stakes .Looks like your man door on the side is the same height as garage doors .Thats what you have to go by or doors won't fit.If your doing all height marks/grade stake I highly suggest having the concrete boss check it way before trucks arrive .

 

[themiller]

I have 1% over my front 20'. I have to chock any wheels if I don't want them to roll. Also allows for all the salt and road crud to drain quite nicely. If I was to do it again - I'd do it the same way. If the shop was for more working and less daily driver - I'd do less slope. My .02.

 

[cdnc]

Run a chalk line on walls .Use a transit to shoot for grate stakes .Looks like your man door on the side is the same height as garage doors .Thats what you have to go by or doors won't fit.If your doing all height marks/grade stake I highly suggest having the concrete boss check it way before trucks arrive .

Exactly - given that the front and rear doors are cut to the same level, I don't think I can actually have a slope in the garage - is that correct?

For the others - thanks for the input, but not wondering what slope to use. That's basically set by local building code and is often 1% - 2% (or 1/8" or 1/4").

 

[BobRae]

My current garage floor is sloped at a bit more than 2% giving me a bit over 5" on 24'. I'm pouring a new floor and will use a 1% slope. I'd like some drainage to the slot drain but with in floor heat I doubt much melt will make it to the drain. I'll wash the floor every couple of weeks to keep the sand out of the mud room between this attached garage and the house but will help drying time by using a floor squeegee rather than a greater slope - that way the garage lift is more level

 

[MagKarl]

Do you absolutely have to have your shop floor sloped? My garage is sloped, my barn is level.

 

[cdnc]

Do you absolutely have to have your shop floor sloped? My garage is sloped, my barn is level.

Good question. About 1/2 and 1/2. I'd like to slope where tractor and truck will be parked. After things like snow blowing will be a lot of water (gallons) combined with cold climate want to move it out.

The the part is more workshop area and needs less slope.

CDNC.

 

[On-Wheel]

I'd have it sloped only 22-24' (more if plow is on truck ) in from doors.Where truck and tractor is parked.A little high between truck and tractor and high on sides,your actual floor height.Just remember ,there's only 1 chance to get what you want without tearing it out.Tell them what you want.Water test it ,if not right? Have it all in writing if not right they fix it.
Good luck

 

[zporta]

Thought I would post a pic to clarify. From the top of the foundation wall to the bottom of the cutouts is 12". From the header of the door to the bottom of the cutouts is 10' 5". The slab is 5". The distance from the cutouts to the garage trim piece is 5".

Thoughts?

What cutouts are you talking about?

 

[welder4956]

Exactly - given that the front and rear doors are cut to the same level, I don't think I can actually have a slope in the garage - is that correct?

For the others - thanks for the input, but not wondering what slope to use. That's basically set by local building code and is often 1% - 2% (or 1/8" or 1/4").

Slope from center of slab toward doors?