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Forum topic by agallant posted 11-11-2014 03:48 PM 1171 views 0 times favorited 15 replies Add to Favorites Watch
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551 posts in 3062 days

11-11-2014 03:48 PM

Wife and I are looking at building a detached 2 car garage for my shop with an apartment above it. I have a few questions.

1. Anyone do this before if so can you share your thoughts
2. How flat does the land need to be to pour a slab? Can thicker concrete make up for a difference in grade of say a foot or so?
3. I am seeing cost all over the place from 11K to 50K
4. Worst case if its to expensive to grade we may just do a pier foundation on concrete footings.

Any input would be helpful.

15 replies so far

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7739 posts in 2182 days

#1 posted 11-11-2014 03:53 PM

Using “thicker” concrete will add a lot to costs. You can back-fill with gravel to make the ground more level, then pour the concrete. That’s what I did when they put in my pole barn up in TN.

-- Perform A Random Act Of Kindness Today ... Pay It Forward

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551 posts in 3062 days

#2 posted 11-11-2014 04:13 PM

More than a retaining wall with back fill?

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92 posts in 1675 days

#3 posted 11-11-2014 04:52 PM

Put footings in, how deep depends on how deep your frost goes down in winter. footings support you structure, back fill with gravel and compact it at least 6 inches for drainage. next a vapor plastic then 2 inch styro foam for insulation. Slab of 4 inches with mesh and rebar should be all you need. Floating slabs are ok if you have footings to hold it in place. good luck. 50k would build me a shop to die for. :)

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590 posts in 1539 days

#4 posted 11-11-2014 04:53 PM

When you run electrical, go 250 amp or higher!

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Bill White

5106 posts in 4136 days

#5 posted 11-11-2014 05:51 PM

Be sure to add water supply, recepts at 4’ above floor, insulate like crazy, dbl. pane windows and insulated doors, at least one double door, and 9’ ceilings.
Aren’t I good at spending your money?


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4032 posts in 3146 days

#6 posted 11-11-2014 05:55 PM

I had a slope of 18” one way and 6” the other over a distance of 16’ and 24’ respectively. So I built a 16’ x 24’ on piers spaced on 8ft centers, set in concrete. Floor joists are 2×10s spaced on 12” centers. There is a beam down the middle so my joists are only 8ft long. This setup is solid as a rock. I love it.
I have an attic with an upstairs office. The shop area has 9ft ceiling ht. Building this shell with Hardie plank siding, cost me about $12,500 in Tennessee, done by local contractor. I’m doing the wiring, plumbing, insulation and interior finishing myself.

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551 posts in 3062 days

#7 posted 11-11-2014 06:01 PM

We are hoping to keep it as close to 30K if we can including the apartment buildout. I just spoke with the concrete guy and got a quote of $4,800 for a 30X30 4” slab with grading (no more than 8 inches) price includes the concrete ramps seeing as we don’t have a paved driveway .

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5141 posts in 3419 days

#8 posted 11-11-2014 06:50 PM

Don’t forget to have the slab machine trowled for a smooth “roll-on” surface. I left mine rough as poured and now it’s hard to move machines around. I guess with an apartment above, you will need permits and drawings to submit.

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242 posts in 1723 days

#9 posted 11-11-2014 06:57 PM

You didn’t include your location, but where I live you need a stem wall around the outside, and pour the slab inside that. The stem wall foundation supports the building, the slab is just the floor. Surely you don’t expect to just build the building on a slab? In my location, they use a trencher and dig a 12” wide trench to pour full of concrete, 30” deep, then pour the slab so it overlaps the slab for that type construction. Stem wall type construction is better.

-- Jim from Kansas

View Charlie's profile


1100 posts in 2461 days

#10 posted 11-11-2014 07:04 PM

My slab was poured monolithic. No control joints tooled in. The next morning they came back and saw cut the control joints. It wasn’t machine troweled but the concrete guy knew what I was building on it and his guys stayed and steel troweled the whole thing. The floor is darn near shiney even when dry. The cut joints are a saw kerf wide so things roll over them as though they weren’t even there.

I don’t have a second floor. It’s just a shop. So there are no footers. Just a floating slab. The edges are haunched so the entire perimeter is about 16 inches thick about a foot … maybe foot and a half in. I believe if you’re going to have an apartment above, you’re almost surely required by code to have footings below frost level.

For your out-of-level grade condition you can dig it down on the high side and just remove any sod on the low side. On the high side you lay a couple of courses of block to bring you above grade for framing. On the OUTSIDE of that high-side wall you lay some drainage pipe, wrapped in fabric, and then back fill what little are you have against the building with stone. The main thing is to make sure you have masonry projecting above grade so you never have dirt against your sills.

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551 posts in 3062 days

#11 posted 11-11-2014 07:21 PM

I live in North Carolina. Im not sure if there is even a frost line here.

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1317 posts in 2110 days

#12 posted 11-11-2014 10:32 PM

1. Try to manage a wood floor of some sort, even if you just put 2×4’s on edge and put 2 layers of 3/4” plywood over that as your floor. I’ve always had concrete floors in my shops and it wears on the feet. I’ve heard wood floors are much easier on the body (and on your sharp tools when you drop them). This might also give you a shot to save some money if a pier and beam foundation is cheaper than a concrete slab.

2. Put some windows in there. Nothing beats natural light for working and for keeping your mood up.

3. Make a driveway up to it so you can move stuff in and out easily.

4. Plumb it.

5. Install some sort of HVAC and insulation, so you can keep it between 55 and 85 or so. That is a helluva lot better than 25 and 105. Worth every penny in my mind.

6. Plywood or shiplap walls to screw into. and paint the walls white. Makes you feel less like a caveman and more like a craftsman (even if you are closer to a caveman…)

7. This on is my favorite- Put full size garage doors on BOTH ends. I know it sounds nuts, but I had this in my first real shop and I loved it more than any other feature. Multiple reasons: a) On nice days you can have a nice breeze blowing thru with lots of sunlight (seems like NC would have plenty of nice days compared to many other parts of the country) b) When applying finishes, just open the doors and the fumes will clear out. c) When the shop gets dirty, open both ends and use the leaf blower to clean it all out. d) When using power tools, the wind tunnel effect does a much better job at getting rid of fine dust than any high dollar cyclone ever could. Chip collection is still necessary, but it is much more bearable than a closed in shop.

Sorry to rant, hope this helps.

-- The Wood Is Your Oyster

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1060 posts in 2762 days

#13 posted 11-11-2014 10:42 PM

I built my 33X30 garage with a dormer, water, sewer for bathroom and 200mp service cost $34,000. See my workshop to get a picture.

View bigblockyeti's profile


5256 posts in 1896 days

#14 posted 11-11-2014 10:54 PM

My parents are in South Carolina and did just what you’re planning on, they were into it for ~$60K, but it was just under 800 sq.ft and could have been built more cost consciously. It was on flat land, on a slightly sloped lot as yours, you might consider having a footer dug, blocked up and back filled with gravel before pouring the slab. In my experience your best bet might to be able to find someone who has the knowledge and equipment and can do it as side work. Paying someone cash on the side as you go (or after completion, NOT up front for a side job) can be a real value for you and who you’re having do the work. +1 to the walls being painted white, my shop has 7/16” OSB painted white, and it reflects light much better than if not painted. Plan for lots of 240V outlets. Include plumbing if you haven’t already planned that for the apartment.

-- "Lack of effort will result in failure with amazing predictability" - Me

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1060 posts in 2762 days

#15 posted 11-12-2014 12:29 AM

There is a one bedroom, full bath and kitchenette in the upstairs apartment . I use it when family comes to visit. I do not want to worry about shop noise and pleasing renters.

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