20x24 build - forms and slab questions

[roche]

Hi,

Been lurking for a while, I'm finally ready to build my garage I'm in Canada and English is not my first language, so bear with me.

Brand new house, most of the landscaping is done. It's garage time. I made most of the landscaping myself and the driveway ends up like this:

About 18" of compacted crushed rocks surrounded by a "landscaping" block wall. This is where the garage will sit. Plumbing is done as you can see. I have been doing some reading on the forum (after doing all this, duh) and I have some questions before setting up the forms and pouring. Keep in mind that this will be a radiant heated slab and I will install 2" foam underneath the slab.

1. Most of the slabs I saw here have a thicker edge. Much like this :

My understanding is that it reinforce the slab where the walls are but I'm not sure. As you can see, I did not plan for this in my preparation. Would a ~7" concrete slab require this? Is it possible to simply lay the insulation level and pour?

2. I plan on a 1" slope/drop from perimeter to center. Is it enough? Drains are legal up here.

3. I'm on the fence when it comes to mesh vs. rebar. What's your opinion on this? Rebar sounds like the way to go but much more work for a novice.


Thank you!

 

[Gary S]

Building code here requires slab to look like more like your second picture. I don't remember the exact dimensions, but the thickened edge is somewhere near 12-18" wide and deep while the floor of the slab needs to be only 4".
This seems to work well in extreme temperatures of -45 to +115.

 

[dirttracker18]

Where are you located?

Here an 18" perimeter depth was required and my inspector insisted on rebar, although I was going that route anyway.

In floor heat rocks, especially up here

Your slope should be sufficient as well I would think.

 

[ETpilot]

I think that before you go any further you need to check to see what the building code for you area specifies. Unless, where you live there is no building code. If you have a code, you have to comply with the requirements or you will have some headaches to contend with.

The thicker area on the perimeter of the slab is the footer. It is made larger and with rebar to support the walls and roof of the building. If you look at that second picture you will see 2 vertical stubs. These are threaded studs placed in the footer. The wall sill plate is drilled, placed over these studs and a nut and washer secures the wall to the footer. Mesh is usually used in the slab.

Make sure you run any electrics also before you pour.

 

[roche]

I'm in Quebec and the way I see it, there is no specific code about garage construction. There is no inspector also.

That said, I want to build something that will last and makes sense, code or not.

I did run electrics, thanks!

Let's say I would go the footer route. Any tricks to break down compacted crushed rocks?

 

[cyamaha2007]

you could use and post hole diggers to dig a trench footer. I would dig a footer if i were you. The slab you pictured is a floating slab and if the building was attached to it if wouldnt be legit, Your slab prep as it sits now is how a pole barn floor is poured, it can be a floating slab since the concrete floor adds nothing to a pole structure since the poles go 4 feet down and sit on a compacted rock base or a "pill of concrete" therefor that is the "foundation or footer" Will this be a stick framed building? If so you should read up on a monolithic pour. That is pouring the slab and the footer at the same time. Good luck

 

[CanuckGT]

I`m in alberta,Canada and here, any garage over 100sq meters has to have footings a minimum `4ft in the ground, looks like yours is over thus I assume you need to dig 4ft down and pour footings.

I am currently building myself and down sized to 28x38sq ft to get around the footings and go with the thickened edge 18x18in with 4 -10mm re-bar edges and 16x16in 10mm rebar grid for the slab which will be 5in.


Oops, just re-read your post and noticed the size...my bad. You should bed good with a thickened edge slab.

 

[ETpilot]

Here is a link to youtube videos on footers, slabs and other info that may help.

Videos

 

[kartracer23]

You can't use just any rock - especially on a slab w/ integrated footer. You need something super-solid. They used a reclaimed concrete on mine and after compacting it, it felt like cement. You could jump up and down and there was absolutely no give. Kicked up a little dust, but that's it.

With an integrated footer, the weight of the building is pressing down on the outer edges so movement is more likely. My old garage was on-slab and the center of the concrete, down the middle of each bay where the control joints were, was pushed up 3"-4" from settling.

 

[roche]

You can't use just any rock - especially on a slab w/ integrated footer. You need something super-solid. They used a reclaimed concrete on mine and after compacting it, it felt like cement. You could jump up and down and there was absolutely no give. Kicked up a little dust, but that's it.

It's rock solid right now with the compaction. I could roll on it with a bulldozer.

 

[joes169]

I would plan on digging the perimeter out for a 12" thickened edge to carry the extra load of the garage walls, and use the excavated gravel to build the center of the garage floor back up to about 4-5".

As for the drain, 1" of drop over 12' of run is going to be pushing the limits without some expected "ponding" of water for any crew other than the absolute best. IMO, it's asking a little too much, and 1.5" to 1.75" will work far better w/o any real disadvantages.

 

[fredybender]

I am also from Quebec, and I have the outer perimeter at 12"
You can just add "DB" stone in the center, but it will bring your garage 6" higher (not a bad thing IMHO)
I stongly suggest you have 12" perimeter thickness: with our winters, you can't beat over-engineering
As far as rebar, I heard that only rebar is structural, not mesh. but nothing beats talking to competent concrete contractors.
Good luck

 

[roche]

Thanks for your opinion all. I followed your suggestion

Forms will be up this week. Can't wait.

 

[cyamaha2007]

Good call youll be glad you did it right,