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How deep to dig for cement slab with steps


This is my first project with cement. From my front door I want to build a 5' x 7' landing with 2 steps leading to my city side walk. The cement slab needs to be 14 inched above the ground to reach just under the front door. I live in Montreal, Quebec, Canada where the temperature in winter can go to - 30 Celsius, very very cold. Do I have to dig 4 feet down, that is the frost line, or will 10 inches do? Once I have my hole I will build a wood form to keep the cement in, add crushed stones, plastic sheet, wire mesh, then pur the cement in. The cement will be delivered by truck. The plastic sheet is to slow down the cement from drying to fast.


Re: How deep to dig for cement slab with steps

Pascal .... welcome to the forum.

You probably want to check with the building department on your requirements.
While I'm not intimately familiar with the codes in Montreal I understand they can be fairly strict there.

Having said that .... it's not likely 10 inches would be acceptable .... it's more likely a continious footing will likely be needed at least 4 feet below ground level..

Good luck. :)

Re: How deep to dig for cement slab with steps


Yes, welcome.

I tend to agree with canuk on this one.

I did this project 2 years ago, but in my neck of the woods, we don't get temps down as low as Montreal.

There's a lot of physical labor in a project such as this, but I do think it can be done as a diy project.

I found that 95% of the work involved digging, screening soil to separate stones, mixing concrete, or ordering it, shoveling rubble, building wood forms---and only a tiny, final amount of time was spent actually working with the wet concrete.

If you approach the project with the importance of the preparatory phases, you will do very well.

It sounds like you have a good plan, but check with the building dept. & also with local concrete contractors for tips on how to proceed.

Sounds like it's about 2 cu.yds. of concrete needed (<2 cu.metres??), if I read your post correctly.

I used the rubble from the old steps & screened the excavated soil to get the rest of the crushed stone I needed for the firm BED that the slab will rest upon--I used the extra screened soil to fill in other yard areas.

Important to TIE THE NEW STAIR CONCRETE SLAB TO THE EXISTING HOUSE FOUNDATION---this is done by drilling 2 holes right thru the house foundation (HD has a good tool rental for this) & using expoxy to attach 5' lengths of 3/4" rebar to tie in with the new pour---this will prevent the new slab from "wandering" in frost heaves and even minor ground settling---extremely important step that a lot of people overlook.

Pitch steps by 1/4" to allow rain to runoff---check with torpedo level.

Any frost heave problems will depend on how well your soil drains in that area, the use of the crushed stone as backfill, & the stability of the ground--the plastic poly sheet will help improve water runoff---if the ground under the slab doesn't drain well, the water content will freeze up in winter & heave.

Sheetrock or deck screws with an elec. drill fitting (with reversing chuck) are much better than nails when fastening the wood forms & they can be removed more easily for future use & won't harm the wood as much---lots faster, more secure assembly.

The ground directly below the slab has to be checked beforehand for any underground utility pipes (water/gas)--they usually do this free of charge---if any gas/water shutoff valves are directly below the slab, they must be extended up to the slab surface to allow access (they can't be covered by the slab).

Use plastic sheeting taped to the house for protection to cover the door & house siding if you order concrete by truck---there's always a lot of spattering of fresh concrete from the chute & can be hard to get off siding.

If you need iron railings for the new stairs, sink 8" plastic pipe sections into the sides of the steps for this before the concrete hardens.

The vertical step risers themselves should be tilted slightly towards the street to increase thread area----this gives the stairs a much better appearance---the osborne site below deals with this issue.

Hit the forms lightly with a rubber mallet all over after concrete truck leaves to settle & vibrate out any unseen small cavities in the wet concrete.

Make sure you BRACE ALL THE FORMS with sturdy 2 X 4 or larger lumber members---the concrete truck guys often just want to pour the mix in as quickly as possible & this can easily burst the forms---have a few extra pieces of staked 2 X 4 forms ready at pour time---if you hear a crack, stop the pour & reinforce the forms where needed.

If a form does burst, all is not lost---the important thing is not to panic---the wet concrete will sit quietly on the ground while you reinforce the damaged form---simply take a long-handled shovel or use a plastic pail as a scoop & put the wet concrete back in the form.

The wet concrete should remain soft for at least an hour--even on a warm day (much longer in cold weather)---that gives you plenty of time to work it.

Let us know how the project goes, & if you need any help.


Re: How deep to dig for cement slab with steps

Hi Everyone

Thanks a lot for all your advice. I will go and talk to the city folks. I was hoping to avoid this since they are open during working hours.



Re: How deep to dig for cement slab with steps

Hi Everyone

Thanks a lot for all your advice. I will go and talk to the city folks. I was hoping to avoid this since they are open during working hours.



Re: How deep to dig for cement slab with steps

I know this thread has been made long ago, but I am currently in the same situation and was wondering what happened when you went to visit the city?
What was the final answer as to how deep you had to dig?


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