Grading / Draining options

[scoob8000]

First off, my apologizes for all the newb threads popping up from me here.
We're in the midst of our first garage build and I've got a ton of questions..


We're doing a pole building with floating slab floor. Garage is situated on a flat spot on a hill that sees quite a bit of water during the rainy season.


The contractor moved the dirt and set the posts while I was at work. I would have liked to had more level ground before the slope starts. I have 4ft in the rear and almost 2 on the side. At most there is a difference of 4-5 ft of elevation from the floor of the garage to the top of the slope.


A few thoughts that I've had are:
A. Rent a machine and grade the hill back a few more feet to match the rear, (Giving myself 4ft all around) then install the french drain.

B. Leave the slope alone, build a small foot wall around the flat spot and put the drain at the base of it on the slope side. (But in the long run, I'd really like to be able to get a machine around the garage if needed)

C. Leave it as is and put a drain pipe in the existing flat spot.

Whatever dirt I move can easily be used to build up the other side of the garage which is very low.

 

[MagKarl]

I would want to do some more grade work if that were mine. I would start by cutting deeper and away from the shop so that the grade slopes away from the building for several feet on all sides. At that point you can decide whether to grade a surface ditch/swale or dig for a pipe. The right answer may depend on whether we are talking about ground water or surface runoff.

 

[36truck]

I would cut the hill side down. Give yourself a good 8to 10 feet of space between the building & the base of the hill. Slope away from the garage so water drains by itself. Like you said use the extra dirt to fill in the low side. Save the topsoil to reuse when done.

 

[shocker998md]

Im fighting raining at my house now. You definitely need to cut more and have the building be the high spot. The water will collect there if you leave it as is.

 

[justin1795]

I would shape it as a v so the water goes one way or the other. I would consider putting some large drainage pipe around the building also im fighting similar issues but my problem is slightly different.

 

[tomshep]

Do it once and get it done right. I would grade back and create a swale that would divert the water so you don't have to worry about drains, ,etc.

Tom

 

[rocklobster]

Option A: More time and money but done right first.

Plus you get to play with a bit of earth moving equipment.

 

[kursplat]

I like "A" but would cut back more. 6'-8'
"B" is bare minimum.

was there anything in the contract about what grading would be done?
have you talked to the inspector about what they're going to want?

 

[Rookie2]

You will need a french drain , your already funneling water toward and under your slab which will freeze. Then snow will collect on the roof and dump along the sides and saturate the soil even more. I have sandstone but I still cut in a drain and filled it with 2b gravel.

 

[theoldwizard1]

I like "A" but would cut back more. 6'-8'

+1 !


Your French drain should be at least 1' wide and 2-3' deep. Line it with HD landscape cloth. lay in a couple of inches of 3/4" crush gravel (use it to adjust the pitch). Use 4" solid (not corrugated) drain pipe inside of a sleeve. Cover with more 3/4" gravel up to a depth of about 8-12". Fold in the landscape cloth and cover with dirt. If you are concerned with surface runoff, fill completely with gravel.

I hope you have a a large place to send all of the water ! You will be surprised how much water will come out that drain !

 

[NUTTSGT]

I'll echo what the others have said, cut it back, French drain or swale to help divert the water around and away from your shop.

 

[Farmall450]

+1 !


Your French drain should be at least 1' wide and 2-3' deep. Line it with HD landscape cloth. lay in a couple of inches of 3/4" crush gravel (use it to adjust the pitch). Use 4" solid (not corrugated) drain pipe inside of a sleeve. Cover with more 3/4" gravel up to a depth of about 8-12". Fold in the landscape cloth and cover with dirt. If you are concerned with surface runoff, fill completely with gravel.

I hope you have a a large place to send all of the water ! You will be surprised how much water will come out that drain !

+1, the neighbor's yard will do

 

[buddyboy]

no way you can leave as is

if it's mine I would cut it down to drain away from the building on all sides

the highest point of your swale needs to be at least one foot below the bottom of your lowest skirt board.

In other words go out 6 to 8 feet from the building and cut/fill to make it at least 1 foot lower.

as others have said you should have a swale to divert the water around the building.

a pole building should be 1 foot above grade before construction and finished grade would be running away from the building on all sides

 

[scoob8000]

Sorry for the untimely reply. Worked a couple 16 hour days last week and still trying to get back to normal.


The low side, and garage door side are always going to face downhill. That high side is my biggest concern.

The pickle I'm in is my property is only 75 feet wide. I have about 30 feet to the property line on the high side. I'm afraid if we cut back too far, the bank is going to be too steep to ever mow. I'm almost thinking a skidloader bucket width level, then taper into the hill.


Buddyboy,

1ft deep sounds good for the drain, how far away from the posts? About the same?

 

[theoldwizard1]

I have about 30 feet to the property line on the high side. I'm afraid if we cut back too far, the bank is going to be too steep to ever mow. I'm almost thinking a skidloader bucket width level, then taper into the hill.

Sounds like you need a 3-5' retaining wall !

If you go that way, don't cheap out ! You a foundation of some kind (for short walls, you can usually get away with one block below grade), and good drainage behind the wall.

Some type of drainage is still required for the lower level.

 

[earthworks]

i don't know if you found a solution but here's a couple pics of a garage i built this season where i had to cut into a slope. I did what you said, about a skidsteer bucket width away, put in a weeper and sloped away from the slab then built a retaining wall with the stone i excavated from the site.