Garage Foundation Choices

[danmor]

Hi!

I will have a 25x25 garage built on a 25% sloped lot. Low side slab floor will be ~2' above grade, high side 6' below. I will have living space above. From what i've read, I would need footings with a stepped stem wall and a slab. This would then be 3 separate pours? Is this the best option? Average frost level is 12-18".

Thanks,
Dan

 

[larry4406]

Yes 3 pours if traditional footing, wall, and then slab.

 

[ConCretin]

Really no any other way to do it given the grade change. A stepped footing and wall followed by the slab. Just curious why the front edge of the slab will be 2' above grade. Are you intentionally building up the access drive?

If you are in frost country, you'll need to maintain a minimum footing depth relative to exterior grade. The footing will need to have frost cover at the 'low side' but can be right below the slab on the 'high side'. Your probably want to step your walls to hold your framing up from exterior grade without too much exposed foundation.

You'll want to consider drainage and possibly waterproofing on the sections of wall where exterior grade is higher than slab elevation.

 

[Jking24]

Your not required to have a step footing it's just cheaper from a material standpoint. The requirement is generally just that the bottom of the footing sit on undesturbed soil at our below the frost line. I have a similar situation although not as aggressive of a slope. Mine was like 2 above 2.5 below and we did the complete footing at the same depth. Used more block and concrete but didn't have to do any framing in the footer trench and it made the block work easier. My personal opinion is if your gonna have any issues with your footing it will be where it steps up or down. If you gonna do a monolithic some places will let you do the walls and footings in one pour. If doing this your self just make sure you check with your local code office/ website. Most places have a maximum height of unequal fill before an engineer needs to sign the plans

 

[danmor]

Thanks for the comments. Didn't see them until now. Either don't have the email notification enabled, or it doesn't work.

The garage slab, which is now 28' wide, would be 2' above grade on the low side for a couple reasons. 1) it is already a steep drive, 16-25%. 2) a good place to put some of the excavated fill 3) I don't know any better.

Dan

 

[Fastie]

Am curious of cost of this type of foundation. I am building a 26 x 32 ft long garage. The garage will be level with existing driveway and then slope down about 3ft in height to the 32 ft length. I am struggling finding a good contractor in my area - but trying. Building a pole barn structure on top of this block or concrete foundation. Would love to hear how your project worked out and cost approximately I can expect.

 

[CraigStu]

7 yrs ago we had an extra bay added to a 2 car garage, The contractor said that if the finished slab was >2 ft above the normal grade then engineering was required and that usually ended up needing the slab supported by piers. A LOT of extra expense. We were able to avoid that by having the new bay floor 3 ft lower than the existing bay floor.