Slab above grade or below grade with block wall?

[Hoops.]

I am planning on building a 24x36 storage garage soon, and I will be building it in my backyard which has a slight slope, about 24" in grade change over 36'. The back is higher than the front. Since this is a gradual hill, I do not want to have to worry about water coming into my building. I'm thinking of either:

1) Put the monolithic slab 4" above the highest point of the grade. Meaning the front of the garage will be about 24" above existing grade, and I will have to do some grade work to make it look and function properly.
2) Put the monolithic slab 4" above the grade at the front of the garage(the back would be below grade), and add 2-3 courses of concrete block to the walls. I am leaning towards this as I feel it would look better and require less grade work. I also can use 8' lumber to get a 10' wall. Would I have to put anything other than dirt around the block wall to prevent water coming in?

Any experiences with option 2?

 

[pattenp]

My garage is below grade a few feet in the back because of grade slope and I have around 8 courses of block. The key to no water is proper water sealing of the outside of the wall and drain pipe with gravel back fill. I have had no problems with water.

 

[Gary S]

MIne is above grade. I built it that way to prevent water problems in the future. If you put it below grade, the first crack will make a waterway into your garage. If you can guarantee your concrete and blocks will never crack, it doesn't matter.

 

[Garage Dog]

Knowing where you live (i.e. does the ground freeze) and what type of soil (i.e. clay, sandy) you have would be helpful.

Option #2 is certainly possible if the block wall is built, sealed and back-filled properly with drain tile to daylight. You could also consider building a short retaining wall to eliminate having fill against your structure.

 

[Steevo]

The second option, with the back a couple of feet below grade is a very common design.
Just make sure the perimeter block foundation wall is a good foot or more above grade, properly sealed on the outside, has a good gravel/drain pipe system along the entire back and sides, and that you grade behind it so that the first few feet slope away from the building.

 

[ed_h]

My sure-fire recipe for leak-free below grade block walls:

1. Lay concrete blocks in the conventional way. Use a full mortar bed for the first course.
3. Parge outside surface using a rich sand mix. Include a generous filet between the wall and the footing.
4. After the parge has set, spray on conventional black waterproofing compound.
5. Trowel on fibered roofing cement 1/4-3/8" thick.
6. Cover with 6 mil black poly sheet. Extend poly sheet under sill plate on top.
7. Lay perforated drain tube around perimeter, making sure that drain slopes to exit, and the highest part of the tube is below the first course of block. Tube should be surrounded by filter fabric and/or course gravel or crushed rock. The poly should extend down below the tube.
8. If there is a heated space on the other side of the wall, stick on rigid insulation panels outside.
9. Backfill.
10. For any parts of the wall that remain above grade, provide some protection for the insulation or the poly.

Used this method on my house 27 years ago. I don't have gutters (don't like the looks of them), and never made any particular provision for surface drainage. No hint of moisture in the basement so far, even with a few inevitable settling cracks.

 

[kbs2244]

I would go with option two and follow ed h’s procedure for the ground work.
But I would absolutely go with gutters.
Run the back downspouts to the downhill side of the garage.
Put them into a swale or drain tile if possible.

The dirt will stay a lot dryer if the water never gets to it.

 

[pattenp]

While eh_h's wall sealing method will work, it is labor intensive. Use a waterproofing membrane engineered for the purpose.

http://www.certainteed.com/products/foundations/waterproofing/311508

 

[Clik]

I don't know what climate you are in but shops that I've had built into a hill were much, much cooler in the summer and much warmer in the winter. I never had to worry about stuff freezing or getting too hot. I've got a newer steel sided pole barn in Southern Maryland and it gets like an oven in there even though it's got some shade during the day. I would suggets putting foam board insulation on the outside wall below grade if it's deep as it may condensate in humid weather. I didn't mind as it kept humidity off tools and cars like a free high efficiency dehumidifier.

 

[Hoops.]

Thanks for the reply guys.

I'm pretty much convinced going below grade is my best option. I'm looking at a grade pitch of 2' over 36'. A lot of good options for sealing the block.

When laying the block, what sort of rod do you set in the concrete to attach the block to? I assume its a rod I would cut and tap to the appropriate length to hold the sill plate down. Or just use threaded rod?

 

[kbs2244]

When they pour the slab have them place “L” shaped rebar around the edge where the block cells will be.
The masons will fill those cells to lock the block to the slab.