Pilings under the 30x30 slab or not????

[Paul-ish]

I have no clue about concrete and am getting mixed answers for guys in the trade so i'm looking for another opinion.

By city minimum code I need 6 inches of compacted gravel, 4 inch slab with 16x16 thickend outer edges. Kinda like this but with more rebar...


I just had 2 concrete guys come and look at my site. One says this is fine...The other says I need concrete pilings or it will crack all over...

So what's the best way of doing it...I plan on using this garage for the next 30 years...

 

[Stuart in MN]

A thickened edge slab like your picture is generally okay for a detached garage but it depends on the copndition of the soils in your area along with local building codes. Can you check with your local city hall to find out if they have special requirements? I would think pilings are only required in very unstable soil, in which case a civil or structural engineer may be needed to specify them.

 

[Paul-ish]

Yeah it's detached and well soil is hard like clay. Not sure if the one guy was just tring to get a bunch more $$$$ out of me but he strongly recommended pilings.
Get really cold here in the winter and real hot in the summer...Not sure if that matters?

 

[Paul-ish]

More imput please...Anyone?

 

[brownbagg]

no piles

 

[nehog]

By city minimum code I need 6 inches of compacted gravel, 4 inch slab with 16x16 thickend outer edges. Kinda like this but with more rebar...

I just had 2 concrete guys come and look at my site. One says this is fine...The other says I need concrete pilings or it will crack all over...

So what's the best way of doing it...I plan on using this garage for the next 30 years...

Your description and image shows a floating slab. You do not want pilings with this because the slab won't float if held with pilings and will likely fail. You can either do a full frost footing (footing below frost line) or a floating slab, but pilings with a floating slab mixes the two! My floating slab is just fine, no cracks other than with the control cuts.

BTW you do want rebar in the concrete, not mesh.

 

[theoldwizard1]

A thickened edge slab like your picture is generally okay for a detached garage but it depends on the copndition of the soils in your area along with local building codes. Can you check with your local city hall to find out if they have special requirements? I would think pilings are only required in very unstable soil, in which case a civil or structural engineer may be needed to specify them.

Stuart is correct. Check with your local building inspector.

Get really cold here in the winter and real hot in the summer...Not sure if that matters?

Footing need to be down to below the frost line. Where is that in your area ? Probably between 1.0 and 1.5 meters

 

[wssix99]

Your description and image shows a floating slab. You do not want pilings with this because the slab won't float if held with pilings and will likely fail. You can either do a full frost footing (footing below frost line) or a floating slab, but pilings with a floating slab mixes the two! My floating slab is just fine, no cracks other than with the control cuts.

+1. Restraining a floating slab with pilings will cause structural stresses (which its not designed to handle) and cracking.

 

[Daniel Dudley]

If you run 10 inches of gravel, and make sure you put in drainage if needed, you will be fine. Some people would run 2'' blue foam around the perimeter, but gravel is fine.

BTW, you don't want a guy who say it can't be done doing the job. You want the guy who does it all the time and has no problems.