I just had a severe blockage in a kitchen drain pipe (40 years of cooking grease accumulated) that required a section of concrete floor in my basement be removed to replace a section of pipe. My question: the plumber backfilled the 2 foot deep hole with rubble from the floor he broke up. He then put about 2 inches of new concrete on top of the rubble. Will this be stable? Does it comply with the Building Code?
There's nothing in the Building Code that specifically relates to basement slab thickness. However, 5" in Ontario is the standard.
The backfill he used may be sufficient, however it depends on how large the aggregate was. Typically crushed rock (the type you see used for driveways) is used. You can use that for comparison in determining if the size used would suffice. It likely will. One point to note is that the size of the area replaced along with the size of the aggregate used (and corresponding air pockets/voids) left under the concrete along with depth of concrete used will all factor in to determine stability. Also, remember that concrete is liquid and will fill any void readily available to fill so that your floor, despite what you may have seen is in all likelihood just fine.
As noted by another poster however, if you are questioning the work, it is best to contact your local building department, who given the work done, should hold a permit for the job already, to inspect the work. Or, you can call another contractor to come in and redo the work or request the existing contractor redo their work.
All Canadian building codes are based on the National Building Code with each province adopting certain revisions. In all likelihood the rules in Ontario are the same as Alberta where floor slabs are required to be min. 75 mm (3") thick (article 220.127.116.11).
Using the concrete rubble as backfill is permitted by Code. The important thing is that the pipe is suitably supported (normally bedded in sand or gravel in new construction) and there should be enough fines to adequately fill the voids.
The Code talks about unacceptable materials as materials susceptible to changes in volume due to variations in moisture content or chemical-microbiological oxidation; also that fill should be compacted except for clean coarse aggregate containing not more than 10% of material that will pass a 4 mm sieve.
A minor repair of this nature would likely be exempt from requiring permits (building or plumbing); however best to discuss with your local authority including confirming with your local (provincial) Code requirements.
Safety Codes Officer - Building
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