Frost footings or floating slab 40x60 building?

[reader2580]

I am working on plans for a 40x60 garage with 16 foot side walls. I am trying to decide between frost footings and a floating slab. Frost line is 48 inches and soil is all sand.

The city will allow either, but I am wondering what everyone here thinks?

 

[readhead]

Depends on the type of construction.

 

[K'ledgeBldr]

Insulated mono-slab.

 

[reader2580]

Depends on the type of construction.

Sorry, standard stick built. Walls will probably be 2x6 LSL, but I am having an engineer design the walls to meet city specifications.

 

[Kaizen]

I have the same frost here. I did alaskan slab and don't regret it at all. hairline cracks at control joints but only visible outside on 2 foot stem wall i had them do. no break in the epoxy floor.
doing footings and foundation walls would have doubled my concrete price.
spend extra time trucking in good rock and compact the hell out of it in several lifts.
In my town i only needed footer/walls if i was making a 2nd story.

 

[matt_i]

Is it a clearspan building?

With 16' sidewalls and a clearspan you are building up some loads in the 2 bearing walls.

Its too big of a risk in my mind to put ~$50-60k worth of materials on the line and not be frost protected in some way, either traditional meaning digging below it, or by getting approval to use the frost protected shallow foundation designs that HUD has put out there.

 

[reader2580]

Yes, clearspan.

 

[ConCretin]

I wouldn't hesitate to use a monolithic slab. You could protect it from potential frost movement with rigid insulation but it's not necessary if your soils are stable, consistent and drain reasonably well. Obviously a bit smaller but I have a 28 x32 that performs just fine.

 

[GTFiero]

Norther MI here on all sand. Did 6x6” post on 60” deep 2’x2’x2’ pads and a slab floor. Put 2” foam 2” down around exterior of floor slab. Cut thin control joints in wire reinforced slab. Entire building is 30’D x 60’W x 12’ T. We did 2x6” interior wall studding for 24” batt insulation. the building has been up 4 years now with absolutely zero movement. Most post buildings in this area of sand last many, many years. Glad I didn’t put the extra dollars into footings. Using those dollars for more fun stuff.

 

[Stuart in MN]

Slab construction is pretty common in Minnesota. My garage isn't nearly as big (24x40) but it's held up just fine for over 20 years now.

 

[reader2580]

I am trying to build this garage as economically as possible while not compromising on strength and longevity. If I go with frost footings I most likely will not put in a slab to start with.

The engineer that is engineering my 16 foot tall walls said that technically code requires frost footings due to building size. He also said that a floating slab could work if the city will allow it.

I think frost walls could be done for around $8,000. All the concrete is the killer. My thought is a floating slab might not be that much more than frost walls although my first slab quote was almost $25,000.

 

[Orionrising]

Sand you still need to verify water table depth. It can be excessively well drained or poorly drained and saturated depending on the topography.

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[Kaizen]

I am trying to build this garage as economically as possible while not compromising on strength and longevity. If I go with frost footings I most likely will not put in a slab to start with.



The engineer that is engineering my 16 foot tall walls said that technically code requires frost footings due to building size. He also said that a floating slab could work if the city will allow it.



I think frost walls could be done for around $8,000. All the concrete is the killer. My thought is a floating slab might not be that much more than frost walls although my first slab quote was almost $25,000.

Are you including excavation? No way they can dig down four feet, pour footer, come back and put forms and pour wall then come back and remove forms for 8k. My building is half that size and that was my best quote.
25 k is about right for slab with thickened edge depending on thickness of floor you want.


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[reader2580]

Sand you still need to verify water table depth. It can be excessively well drained or poorly drained and saturated depending on the topography.

I don't know exactly what the water table is, but it seems to be very far down. My house has an 8 foot basement and it stays dry with no drain tile. (If there is drain tile I have no idea where it drains. No sanitary or storm sewer.)

Water seems to drain very quickly. I have dug down four or five feet and not had any water show up in the hole.

 

[reader2580]

Are you including excavation? No way they can dig down four feet, pour footer, come back and put forms and pour wall then come back and remove forms for 8k. My building is half that size and that was my best quote.

My educated guess of $8,000 does not include excavation. This is based on DIY with some help.

The concrete is the expensive part of the foundation. I got a quote of $4,5000 for 27 yards of ready mix concrete. $167 per yard. The concrete supplier didn't know if prices are going up before construction season is in full swing.

I also got a quote for foundation grade SIPs that can sit on crush rock for about $10,500. The SIP panels also require many yards of crushed rock placed on either side of the panels. I think I'll pass for that price.

 

[reader2580]

I have the same frost here. I did alaskan slab and don't regret it at all. hairline cracks at control joints but only visible outside on

I think an Alaskan slab is what is more commonly known as a frost protected footing. Minnesota building code does not allow this type of footing unless the building is heated at all times to an average of 64 degrees F.

 

[Kaizen]

I think an Alaskan slab is what is more commonly known as a frost protected footing. Minnesota building code does not allow this type of footing unless the building is heated at all times to an average of 64 degrees F.

Why would they not and other areas like mine with same frost allow? No matter what temp inside is frost will heave if it wants to


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[matt_i]

I think an Alaskan slab is what is more commonly known as a frost protected footing. Minnesota building code does not allow this type of footing unless the building is heated at all times to an average of 64 degrees F.

It seems odd to me that a slab-on-grade is a possibility (maybe because its ONLY a garage...) and the FPSF is not. The HUD has designs for unheated buildings in its "cookbook" that encompass all of North America.

The heat is in the earth (free for some time into the future) and is heading out to space, its just a matter of how to trap it to stay above freezing.

 

[u2slow]

You might want to estimate concrete volumes for both. The amount you need to get your footings deep enough (48" frostline, but how much further till you hit hardpan or bedrock?) can also build you a stout floating slab.

The other factor with footings is you can delay and plan your floor slab better after the building is up.

Biggest problem with a monolithic slab in my climate is the bottom of the walls rotting out prematurely being so close to grade.

 

[theundermount]

so my father just finished his garage, he went with helical piles, we then sleeved them with PVC pipe and poured a floating slab around them, not wanting any movement of the slab we ended up following an engineer's direction of digging around the slab down 20in and 24in out and used foam board insulation all the way around, we then back filled with stone and topped with soil. engineer was satisfied that this would eliminate any movement of the slab during thawing a freezing. the piles were significantly cheaper than digging a footing or doing post holes with concrete

 

[Marctrees]

So, is all this better than a Menard's, Lester's, pole building w upgrade of Foundation use CCA posts ?

NOT trying to upset the boat here... just curious why OP decided against that.

Marc

 

[reader2580]

So, is all this better than a Menard's, Lester's, pole building w upgrade of Foundation use CCA posts ?

NOT trying to upset the boat here... just curious why OP decided against that.

I can’t do a traditional full steel pole building because I don’t have over five acres. The roofing options the city will allow require sheeting the roof. The extra weight means more trusses. The pole building guys don’t like to support trusses without extra poles. I also have to use SmartSide siding to match house so that complicates pole building.

It just doesn’t really make sense to go with a pole building for me.

 

[matt_i]

Can you do a trenched foundation (meaning you trench with a ditch-witch or mini-ex) and then pour your foundation directly into the slot in the earth, 60" deep to meet code? That's acceptable in MI (which means little, I know) and I know several who have done it successfully. 8" is possible, but literally anyone can do the concrete work with minimal effort if the truck can drive up to the site and the slots are not collapsing due to the soil condition or groundwater.

Then you can form a slab around that easily and pour your floor.

Are you going to have a line of center support columns or is this 40' clear span? My advice above would change on that answer for a 40' clearspan. I think you're getting to the point where you need a wider footing to bear all of the roof loads.

 

[DJF3]

I am also in the planning stages of a 34x60 build, also with 16 ft walls. I am doing a full 48" wall 8" thick on 16" x 8". My quotes for footings are 7 cubic yds, walls 19 cubic yds. I'm going with a 5" thick slab and I've been quoted 32 cubic yards. Hopefully this helps with your volume calculations.

 

[finn]

My 32x54 has a thickened slab. Been ther for probably fifteen years with no problems.

Pretty typical construction, and pipes are buried five feet here to prevent freezing.

The soil is stable, though, compared to some places.