Garage build foundation monolithic or footings

[bgh5469 17]

Hey guys wanted to get some opinions on my upcoming detatched dream garage build. I am planning to have 24x28 garage built for my hobbie shop(wheel horses and cars). My question is what kind of foundation should i do. I am in northern indiana and have been told i can build on a monolithic slab(thickened structural slab on grade) or traditional footings with a floating slab. My local building code allows both types for detached structures.  I  prefer footings since they get below the frost line but they are significantlying more expensive. Does anyone have any past experience with a monolithic slab foundations. I don't want to cheap out on my foundation, but if i go with footings I will have give up some other features I wanted.

[rjg854 11,356]

I built a 24X28 2 story pole barn with a floating slab concrete floor back in '03, I've never had a problem with the concrete floor if that's what you're worried about. Saved lot of money by not having to dig footers. I'm in upstate NY and we get some cold winters.  So that might be another possibility for you.

[stevasaurus 22,713]

I like the footing way best.  I suppose both are good, and both can crack also.  The issue with me...getting below the frost with a footing is important where we both are...and critters will not dig down enough to get under the footings.  Ground hogs will tunnel your whole slab out.  My Dad has the slab, and he spent days in a lawn chair with an air riffle trying to out smart that rodent. 

Edited September 3, 2016 by stevasaurus

[Racinbob 11,048]

I had a 46'x56' pole building in northern Indiana with a floating slab and never had a problem except for what Steve mentioned.

 

With a pole structure the posts are below the frost line. Obviously with a frame structure you need the footers. Whatever you decide I wouldn't let the cost be the only deciding factor.

 

Nice building Ranger

[SPINJIM 1,981]

Results depend a little on your soil conditions.  I have a 24 x 30 pole barn on a slab, and have not had problems with cracking, but the soil has allowed the whole slab to settle and inch or two, and below ground level on one side..   That has allowed water to seep in under the sill plate during heavy rain or melting snow.   So just make sure your slab is far enough above ground level, and on well compacted soil & crushed stone.   You'll be fine with the slab.

 

I also keep a Remington .22 handy for those ground hogs.  They like to undermine the slab.

 

Jim

[ACman 7,618]

Definitely footers are the way to go. Even with a pole barn I'd pour a rat wall , just to keep them critters out . 

 

My neighbor said he'd seen a woodchuck out back . Told him make sure to checkout around his pole barn . His barn only has concrete on one half . Well that critter made himself a nice little home under the slab inside of the barn . Came in under the rear sliding door on dirt side . 

 

If you want want to live trap , wrap the trap with a tarp so it looks like a tunnel .

 

I would have to say woodchucks (groundhogs) are on the top of any farmers hit list !

Edited September 3, 2016 by ACman

[953 nut 55,163]

If you can get a track hoe with a 12" bucket to trench down to below the frost line and form and pour a monolithic slab on grade you will have the best of both worlds, only be paying for a little more concrete and steel. If any fill is needed use clean gravel to avoid settling. Be sure the vapor barrier goes down the inside of the trench several inches too.

[DougC 2,641]

Which ever you decide on use re-rod and not wire in the floor. I went the cheap fill route and poured 6 inches of concrete with re-rod and the floor settled a few inches over the years. If I had used wire, it would have broken and I would have had to broken up the floor and started over. The rod held it together and just have cracks and a slope in the floor now, but it's still completely usable. Mine is a 28 by 30 pole barn with 12 foot side walls so I could put in an electric Rotary Hoist if I wanted to.  

[Wishin4a416 2,191]

Footers below the frost line for sure and it will still move some. My wifes grandfather built on a slab years ago and I have to repoint 1 corner every few years. Just keeps settling a bit at a time. I think slabs are fine in more temperate zones but not so good in areas with severe temp changes.

[Shynon 7,459]

I built my 26x32 garage in 1993. I have 4" of concrete with wire mesh,with a 12x12 footing poured into the slab all the way around the perimeter with re rod imbedded into it. I also added one course of block on top of the slab, then built walls on top of the block. only have the normal concrete cracks. Poured on top of a gravel base. No problems with settling here.

[rjg854 11,356]

I've never had a problem with settling or woodchucks.  I'm built back into the woods and chucks are plentiful, I see them all the time.  There is 6" of runner crush limestone under the concrete, compacted, with a stone French drain around the perimeter for roof runoff.  The only crack in the concrete is where the wood stove was. Good luck in whatever you choose to do.

[WNYPCRepair 1,918]

20 hours ago, 953 nut said:

If you can get a track hoe with a 12" bucket to trench down to below the frost line and form and pour a monolithic slab on grade you will have the best of both worlds, only be paying for a little more concrete and steel. If any fill is needed use clean gravel to avoid settling. Be sure the vapor barrier goes down the inside of the trench several inches too.

 

 

The only monolithic slab I ever did was for a family room in PA, in the suburbs of Phila. We still had to dig down just as deep as we would have for footers, the only thing we saved was labor to finish the footer and lay block to get the foundation above grade. And that may have been negated by having to build forms around the slab. You will also have to use foam insulation around the inside of the foundation and under the slab if it is ever to be used as living space. 

[ohiofarmer 3,265]

 I was part of a project that was a modified monolithic slab pour. the first lift of the pour was a 24 " footing that was poured extra thick  where the steel frame posts were located and 10 inches everywhere else. We had rebar as part of the footer that stuck uphigher than the pour to tie an outer perimeter 2x12" wood band to contain and level the top of the slab. We then put a 7/16" OSB apron that dropped down into the trench from the inside of the band to help contain the concrete/ the band was braced and kickered with 2X4 and metal stakes every 4 feet to keep it nice and straight. The second lift of the pour went about 6' from the top of the forms. The rebar did a beautiful job of maintaining the form height and the kickered stakes kept the top form straight and true.

 

 The cool part of this project is that we embedded the drop apron about an inch into the footer to provide a seal to keep the concrete from filling the trench and then added backfill as we poured the wall and that saved having to build and brace a double sided form we did the same on the inside face and backfilled as we went. Of course the wall had steel and even properly located wire benches and bolts for the steel posts every 20 feet. We poured the walls within 6" of the slab top and then prepped for the floor by tying steel mats. I was the layout man and kept the project square and true. Really the rest of the guys were farmers with a whole bunch of common sense that took direction from me. It helped that the farmer who was the building owner told the older guys that I had the construction experience so there were no conflicts

 

 The day of the 50X150 floor pour, we removed the mats from the middle of the building where the trucks ran and then restored them back as the trucks poured the slab. These finishers said that our perimeter was as straight, square and level as any they had seen for a while. They set fresh pads of wet concrete with a laser every so often and poured the concrete to the lasered points and could empty a truck in about 12 minutes Four hours to get the slab down. The deepest puddle of water on the finished slab was only an eighth of an inch and that is very level. Just amazing. So if you can set a footer and stem wall without the labor of building forms, it is the way to go.

[bgh5469 17]

Wow, Thanks everyone for all of the information and recommendations!  I agree with you guys that if you are doing a pole barn then a floating slab is the way to go.  Our plan was to build a traditional garage but maybe we should consider a pole barn design   The way my last concrete guy explained a monolithic foundation was as follows: They strip the top soil and dig a small perimeter trench and place crushed stone.  Then the concrete slab is placed thickened to 18" at the outer 1' of the perimeter and 6" thick at the center of the slab.  The entire slab would be reinforced with rebar and have cast in anchor bolts at the perimeter to bolt the walls down to the concrete. 

 

What bothers me about this is that building is above the frost line.  So drainage becomes really important because you don't water building up under the slab, freezing and heaving.

 

I found the attached picture on the web that shows the monolithic design.

 

[953 nut 55,163]

7 hours ago, bgh5469 said:

drainage becomes really important because you don't water building up under the slab

That is why you back-fill with clean gravel and have the perimeter grade beam extend below the frost line.