I am in the initial planning phases of building an attached garage. Has
anyone created their own foundation for such a structure. I have been
involved in framing a structure but not the actual foundation building and I
wanted to know if this was something beyond the scope of a DIY'er. I am
aware of all the basics that go into making footings and concrete slabs but
I am specifically interested in gotchas or things like grading the land
especially if there is a steep slope to content with, thanks.
When you make up your reinforcing steel in the footer trench be sure to
add one length of galvanized rebar to the top. Tie it twice to every
piece of rebar it crosses. Stub one end of it up at the point were the
buildings electrical power will enter the building. As long as you
don't line the footer trenches with plastic that will be the best
grounding electrode that the buildings electrical service could have.
Do not substitute a bare copper conductor unless you Cadweld it to the
reinforcing steel. The bare copper does not stand up well to the
concrete's corrosive affects.
"This alternating current stuff is just a fad. It is much too dangerous
Call the local building department. Single story garage should not be all
that hard to do in my area. However I do not live in a earthquake zone, nor
tornados, nor hurricanes, nor snow actually the weather here is usually
If you are going to put the slab on a slope, you need to level the site
first. Removing soil is easy but if you need to build up, do it with base
rock and do it 3-5" at a time, compacting between each layer to assure a
For example if the site is clay, don't just scrape off the high spot to fill
in the slope, you need to use a more stable fill like base rock. Do not
build on uncompacted disturbed soil, use a t least 2-4" of base rock over
even undisturbed soil. This is a garage, so it will see a heavy load (as
opposed to a shed) you will need 4" maybe up to 6" of concrete if the
vehicle is very heavy.
Cracking is unavoidable, provide ample stress relief cuts in the pour. Use
wire fabric or rebar. Try to pour it (each part) all at once or at least
within 1 hour, this may require a delivery of premixed or rental of a larger
(1 yard) mixer.
I don't understand why people insist on this. For a long skinny
sidewalk, maybe. I mean, I could do it, but it would be cheaper
and easier to just build a raised steel walkway. But there's no
excuse for not being able to pour a simple floating slab the size
of a one car garage without it cracking.
People have built oil tankers out of concrete. It's just a question
of making the extra effort.
The biggest problem you will likely face is working/finishing the slab.
You could do the footers as with them it is all in the setup, but once
you pour a slab you don't have much time to work it yourself.
I would personally sub out the foundation - if not, at least hire some
finishers for the slab. Plus, excavating/grading/sub-base will not
likely be a piece of cake.
We built our own detached garage a few years ago. My wife and I poured
the footing and perimeter wall ourselves, then hired out the slab work
Our site was mostly level, so I formed the footings using 2x8's and
2x10's (I later ripped these into 2x6's for studs and blocking. Nothing
went to waste). We were required to install a row of rebar in the
footing, as well as vertical rebar stubs every 4 feet to tie in the wall.
After the footings were poured, I made wall forms using 3/4" plywood and
a 2x4 framework. Each panel was 2'x8'. I fastened these to the existing
footing forms, and tied the tops together. I used long bolts every 4' or
so to tie the inner and outer forms together, through a short piece of
pvc pipe inside to maintain the correct thickness. It worked great. We
also had to install another row of rebar and the anchor bolts at the top
of the wall.
Pouring the footing and wall was frantic and intense work. But it only
took about 30-45 minutes for each pour. We stripped the forms 7 days
For the slab, we set up the forms, installed a 6-mil vapor barrier, and
compacted a gravel base ourselves. The professional crew simply poured
and finished the slab. They had four "experienced" guys working their
butts off as fast as they could. There's no way my wife and I could have
pulled that off on our own. We used fibermesh additive in the 24'x28'
slab, and they did an excellent job of finishing the slab. About five
years later now, and no signs of any cracking.
We reused the wall forms to build the foundation for our house, then I
sold them to a farmer who was going to build shelters for his animals or
As for grading the land, I rented a small bobcat to level the site where
we built our house. It was mostly level anyway, just needed a foot or so
of fine tuning here and there.
I used a simple water level to get the site and foundation forms level.
Did you mix the concrete yourself or did you pay for a mixer truck? Don't
certain localities require a certain grade concrete for footings (etc.) and
are these higher grade concretes something the DIY'er can do themselves?
We hired a company called "Mini-Mix" with a truck that mixes concrete on-
site. We used them for all of our concrete work.
It's an incredible system. You only pay for the concrete you need (no waste
to dispose of), and they can usually supply extra if you underestimate the
concrete you needed (which I did once).
They can remotely control the chute and truck while pouring. So he can
easily put the truck and chute where he needs it. VERY convenient.
Our guy always supplied a 3000psi mix which, I believe, is stronger than
code requires for residential work around here.
As for mixing it myself, not a chance. I've mixed up a few bags for a small
step or something, but you would need hundreds of bags to pour a
foundation. Parts would be setting up before you could get the rest mixed.
On a related note, when we wanted to put pea gravel in our crawlspace, I
hired a company with a conveyor truck. He simply parked in our driveway and
shot the gravel about 50 feet out to our foundation. He could control the
distance and angle while delivering, so he did the majority of the
spreading for us. All I had to do afterwards was a light raking to smooth
These high tech trucks make simple work out of some tough jobs.
The guys who did our slab had an old fashioned concrete truck deliver their
concrete though. :)
Oh, and if you don't mind me asking about what were your material costs for
building the foundation of your garage (and how much to build the whole
thing), and how much of your own time was spend on the foundation and did
you need any special help?
It has been a few years, but I think we spent about $1000-$1500 to pour the
footings and walls. This included the lumber to build the footing and wall
forms, rebar, anchor bolts, concrete, etc. Most of the form materials got
reused in the rest of the building.
The slab itself cost another $1500 to hire out.
The total cost of our 24'x28' garage was about $13,000. That includes
permits, lumber, insulation, sheetrock, electrical, T&G wood for the attic
ceiling, roofing, and tools (air compressor, nailers, etc.).
I'm guessing about a month of "mostly" full time work. This included
digging out areas for the footings, setting the forms, waiting for
inspections, pouring the concrete, and waiting a full 7 days to strip the
It took us exactly one year to build our garage, though 1/3 to 1/2 of that
was wasted trying to find excavators and foundation contractors. Eventually
we gave up and did everything ourselves.
Nope, just my wife and I, while our daughter took pictures. :)
I spent a lot of time reading and studying though, so there was no
guesswork when it came time to build.
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