DIY Off Grid Steel Garage – The Foundation

The Goal

The first thing that I want to think about with any structure is what purpose is it going to serve on our property. Ideally with off grid structures, we want them serve a multitude of purposes.

Purposes For The Off Grid Steel Garage

  • Provide shade and cover for our vehicles, tractor and materials
  • Provide ample roof space for a large solar system to charge electric vehicles
  • Provide ample roof catchment surface to capture quality rainwater for our future house and our garden
  • Provide an organized shop area where I can explore wood working, metal working and whatever building modality my heart desires
  • Provide an area where I we can record video podcasts and an office space for DIYHP
  • Provide an area where we can have workout equipment
  • Provide a greenhouse area where we can experiment with hydroponics or aquaponics gardening

As you can see, I’ve thought long and hard about all the different purposes that this garage will provide for us. The dimensions of the garage are 85’x45′ with a 10′ lean on the length. The footprint comes in at a whopping 4675 sq ft which sounds HUGE but will slowly feel smaller over time.

Foundation

The most important part of any structure is it’s foundation. It must be done right to ensure that the integrity of the building remains over the next decades. This is an area that I want done right and I enlisted the help of a local site prep specialist.

My neighbor Mike had a great experience with Joe Smith from Texas Rock & Canyon when he did the site prep for his house.

I had Joe out to look at the area we were going to put the garage. It wasn’t even cleared out yet so he recommended that I clear out the area myself to save money.

Leveling The Pad

When that was done, Joe was back out to determine the how much sand needed to be moved to create a flat surface. Our lot is on a 3% slope which means over the length of the shop pad, which was about 115′ there is about a 4′ difference in elevation. That means approximately 2′ of soil needs to be cut from the top and placed toward the bottom to create a level surface.

Our soil is pretty well pure sand. There are minor amounts of clay in it but overall it is all sand. Joe had me trench ditches from the top of the pad towards the mid point. The purpose for this was to water that soil and let it infiltrate so that when we moved the sand, it would compact much better.

Cutting 2′ of soil may not sound like a lot but for my tractor, the job proved to be far too much. Plus my experience with grading and site prep is nill so I had Joe spend a few days working on leveling the pad area. He has about 30 years of experience and he did a fantastic job of creating a flat surface for us to build on.

He also had the foresight to create berms towards the top of the pad area so that if water were to jump the banks of the drainage ways, it would be diverted away from the garage. Flooding can easily happen in our area during the monsoon season so this was important to plan for.

A/B Mix

He also recommended that we place between 3-6″ of A/B mix where the garage is going to go. A/B mix is an aggregate mix of rock that when is wetted and compacted, provides an extra level of foundation for the concrete slab. Since our soil does not hold it’s shape very well, this will help ensure that if any sandy areas underneath the slab sink, it doesn’t crack it. Depending on your soil type and composition, this step may be completely unnecessary for you. It is best to consult with a local site prep specialist about the best practices for your area.

We ended up putting down 200 tons of A/B mix to create a 6″ thickness. This was an expensive cost for the garage but like I said earlier, the foundation is the most important part of this build especially considering our soil.

Cost For This Step

  • 2 x 5000 gallon loads of water @ $300 = $600
  • 19 hrs of backhoe work @ $80/hr = $1520
  • 201.5 tons of A/B placed & compacted = $4836
  • Total for this step = $6956
-25%

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