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I think 8” concrete is totally unnecessary for your use. Also, most 6” concrete is actually 5 1/2”, 8” is 7 1/2”, etc. I believe this comes from the days of using wood forms....2”x6”, actually being 5 1/2”. I had 2’ of dirt and clay dug out under my slab and had 3’ of engineered fill(basically sand) hauled in and packed for the base. They lined the perimeter of my building with 4’x8’ sheets of 2” dense foam board for a frost barrier, then put rebar on a 2’ grid throughout the entire building before pouring it.
I am pretty sure he mentioned putting a lift in.

4-6” concrete without rebar reinforcement isn’t thick enough for a decent lift with a 8-10k on truck hanging off of it.

Just went through this with a huge ordeal at work and lifts. Plus personal experience with it.
@buildingup can chime in.
 

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I am still working on my 20x26 telephone pole shed that I've done all the work except the concrete pour, literally just the pour and finish. I put the rebar in. If I was in your shoes this is what I would want to hear

  • your planned building is TOO small. It needs to be bigger.
  • Compression strength of concrete is amazing. 6" floor is MORE than sufficient for anything you might drive unless you have 4x4 tractors, loaded dump trucks, etc. Consider only beefing up areas where concentrated weight is expected (two post lift, walls, heavy shop equip, etc.)
  • Tensile strength of concrete SUCKs. Spend the money on more and/or bigger rebar, not additional concrete.
  • plastic pipe is cheap. Consider plumbing for a radiant floor even if you're on the fence about this. I WISH i would have done this in my shed. Simple pump, a DIY heat exchanger and a wood burning stove and you could heat the building.
  • Shed that big needs at least some drains if not a sloped floor and drains. You will get water in your building from rain or snow. Have a way to deal with it
  • Plastic electric conduit is cheap. Plump penetrations using some elbows and short lengths of pipe. This will prevent wall penetrations keeping things looking nice
  • Speaking of cheap pipe, consider whatever you might like to have through the foundation and lay that before you pour. (see pics below of my 'vise' holder idea)
  • Plumb penetrations at every corner. The pipe is too cheap to not do this
  • Tie your ground to your rebar. Its called a Ufer ground. I didnt do this and wish i would have which is why i'm mentioning it
  • Spray foam unless you can get cheap foam board like I did. Spend the money on spray. Air leaks is where the energy goes and this will cover you.
  • Radiant barrier. Trust me :)
  • Install Gutters
  • i didnt install windows b/c of the cost but a larger bldg like yours will need natural lighting. I'd avoid the clear panels on the roof but definitely consider them on the sides depending on your overhang setup
  • speaking of overhangs, i'm darn glad I have 2' overhang around the whole bldg. Not as modern but i'm going for utility (if you cant tell by the pics)
I'll add more ideas as i think of them...

Yes, it was harder than heck to get the bldg sqaure
No, it is not square
Yes, the concrete chairs are too short
Yes, that is a double 2x24 LVL for the Ridge beam
Yes, overbuilt is an understatement but it houses my truck.
Yes, its too small.



The three things in the floor are some custom square tubing holders i built out of 4" angles to hold 3" square tubing. They are 18" tall and sit flush with the concrete.
This allows me to mount a vise/whatever to the top of ANY 3" square tubing and drop in the hole. I've yet to figure out a good way to keep them down for any vertical force i apply to them but this hasnt been a problem yet.
If you do this, set them 1/2-1" below the concrete floor and then bust them out. Mine are flush which didnt allow the guys to run over them with the troweling machine so the concrete looks goofy around them and is not level either.

 

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JD,
On my barns all concrete has rebar in it. My footings and beams are minimum 12" wide by 24" deep and the slabs are 6" thick. I don't park anything as heavy as you expect too so I think that the 8" suggestion is correct. I have not seen concrete poured inside a building after it was erected like LeonardS's was done. On a slab first type, there is a small ledge in the outer footing for the sidewall metal to sit in-- keeps all water sheeting off the side walls out of the building. My buildings are all welded to plates anchored into the slab when it was poured and it was been tornado tested in 2004. Never lost so much as a metal screw in 18 years. Maybe you can compare a metal building to a wood building construction costs. Down here, metal is almost always used because its cheaper and doesn't require much maintenance over its lifetime.
As for a floor drain, when I built the acft. hanger I had, we had the drainbox formed when they formed for the slab in the center of the floor front to back. it sloped to the rear of the building and out to a trap system. It was covered with removable heavy-duty grates which held up to 40K lbs each. That might eliminate the under slab plumbing you are concerned with.

Lots of great info on this post-- wish I had asked the same question when I was building mine.
 
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Upgrade the PSI strength of the concrete. If locally they use 3,000 PSI, upgrade to 4,000 or 5,000 PSI concrete. No more than 4 inch slump - watery concrete is WEAK. And go with bigger than recommended rebar as previously suggested. Lot of good suggestions have been posted - make good use of them.
 

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Discussion Starter #26
Thanks again to everyone who has provided input; I'm learning a lot and I'm starting to get a sense of what I need to convey to the builder.

I will probably put in a two-post lift at some point, so I will specify that a certain part of the slab be poured/reinforced according to the specs for a 12k lift. That should allow me to decide later which specific lift I want.

I think I will go with a forced hot air system because the ductwork will also allow me to install air conditioning, basically killing two birds with one stone.

As for insulation and moisture control, I'm leaning toward the spray foam type. How do insulation and moisture barriers interact? Does insulation make the latter redundant, or do I still need to specify a barrier? Does it depend on the type of insulation?
 

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I worked in a building once that had the slab heating. When the doors were opened in winter it would get cold, but once the doors shut the building was short sleeve weather again in about 5 minutes. The next building over would take almost an hour to warm up with forced air.

Asking about the cost to heat the two buildings in the winter, the bill was only %25 of the cost of the forced air one.
 

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I have radiant heat in the concrete in my main building, it is awesome.
My storage barn has no heat, 60'x60' 16' to the truss bottom from finished floor. (should have gone 100' long)
14' door to allow pontoon boats on forklift and our 5th wheel in summer.
I run a 14k# forklift with 20'+ boats on it on a 5" floor with wire mesh no issues.
 

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I worked in a building once that had the slab heating. When the doors were opened in winter it would get cold, but once the doors shut the building was short sleeve weather again in about 5 minutes. The next building over would take almost an hour to warm up with forced air.

Asking about the cost to heat the two buildings in the winter, the bill was only %25 of the cost of the forced air one.
A heated mass is a powerful warming force.
 

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Thanks again to everyone who has provided input; I'm learning a lot and I'm starting to get a sense of what I need to convey to the builder.

I will probably put in a two-post lift at some point, so I will specify that a certain part of the slab be poured/reinforced according to the specs for a 12k lift. That should allow me to decide later which specific lift I want.

I think I will go with a forced hot air system because the ductwork will also allow me to install air conditioning, basically killing two birds with one stone.

As for insulation and moisture control, I'm leaning toward the spray foam type. How do insulation and moisture barriers interact? Does insulation make the latter redundant, or do I still need to specify a barrier? Does it depend on the type of insulation?
Look at the differences between open-cell and closed-cell spray foam insulation. I'm not knowledgable enough otherwise i'd just share. That should give you the information you need to make the decision on type of spray foam, vapor barrier, etc.
 

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Open cell is cheaper than closed cell and closed cell is much more resistant to moisture absorption. Closed is more efficient R value too for the same thickness.

When I built my guest house I used open cell inside and shot the underside of the floor joists with closed cell.

IIRC for 2x4 walls filled with open cell was 1.45 soft. Closed cell shot 2 inches was closer to 1.80-2.00 sq ft.


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Open cell is cheaper than closed cell and closed cell is much more resistant to moisture absorption. Closed is more efficient R value too for the same thickness.

When I built my guest house I used open cell inside and shot the underside of the floor joists with closed cell.

IIRC for 2x4 walls filled with open cell was 1.45 soft. Closed cell shot 2 inches was closer to 1.80-2.00 sq ft.


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Well, here ya go.

FWIW - i was able to get 1.5" polyiso foam boards for $7/each. Polyiso is roughly R-6 per inch. I would assume any spray foam you get would have equal, if not higher, r-value. Therefore, 2 inches of the expensive stuff would put you at R-12 (i'm making assumptions, yes). A standard 2x4 house with fiberglass insulation in the walls is R-13, to put it in perspective.

Again, spraying will make your barn will make it extremely airtight. Most energy is lost via air movement not conduction.

Speaking of... i havent seen anyone mention this: buy metal backed, insulated garage doors (EDIT: you did mention insulated doors in your OP). I got an Overhead brand 8'x12' for the shed i showed pictures of. Got R-12 foam insulated, metal backed for $1200 installed. They offered a R-17 but the $/R-value skyrocketed. Given that my walls are only R-9... didnt make sense.

Lastly, i'd at least price out a radiant heat system. It's free to get a quote (or should be!). At a minimum price out how much to install the pipe. A mass of warm concrete will, as Mikey52 pointed out, heat your building back up after you open one your big friggin 16x12 doors. If you end up going forced air ... look into a BIG ASS FAN or one of their competitors. They are low speed high volume fans. They move air mass without creating much of a breeze. You'll want one to move the inevitable thermocline you are going to create with that tall of a shed
 

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Well, here ya go.

FWIW - i was able to get 1.5" polyiso foam boards for $7/each. Polyiso is roughly R-6 per inch. I would assume any spray foam you get would have equal, if not higher, r-value. Therefore, 2 inches of the expensive stuff would put you at R-12 (i'm making assumptions, yes). A standard 2x4 house with fiberglass insulation in the walls is R-13, to put it in perspective.

Again, spraying will make your barn will make it extremely airtight. Most energy is lost via air movement not conduction.

Speaking of... i havent seen anyone mention this: buy metal backed, insulated garage doors (EDIT: you did mention insulated doors in your OP). I got an Overhead brand 8'x12' for the shed i showed pictures of. Got R-12 foam insulated, metal backed for $1200 installed. They offered a R-17 but the $/R-value skyrocketed. Given that my walls are only R-9... didnt make sense.

Lastly, i'd at least price out a radiant heat system. It's free to get a quote (or should be!). At a minimum price out how much to install the pipe. A mass of warm concrete will, as Mikey52 pointed out, heat your building back up after you open one your big friggin 16x12 doors. If you end up going forced air ... look into a BIG ASS FAN or one of their competitors. They are low speed high volume fans. They move air mass without creating much of a breeze. You'll want one to move the inevitable thermocline you are going to create with that tall of a shed


Your comment about airtight is right on. And with the humidity we have here I have to run dehumidifiers in addition to the AC because of how tight it is and how well insulated. Ac doesn’t run long and hard enough often enough to keep the humidity down.


Sent from my iPhone using Tapatalk
 
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