In the process of doing a fence in southern Ontario by Lake Erie, I have dug my holes to 42 inch's depth, which I know will be fine for frost depth. The customer is saying it should be 4ft which I know is correct for foundations but I have set post to 42 inches all the time and have had no problems. We are also in clay so not sure if that's making a big difference.
Any insight would be awesome!
Filling hole with all concrete and 6x6 post, the height of fence will be 6'6" and 42 inched cemented.
For my own part, I would say that neither of you are wrong in that posts should be set to between 42" and 48", so in your case, while I can imagine the work to dog further is a bit of a setback at this point (hopefully you haven't returned the auger if you rented it), but sinking it the extra 6" to satisfy the customer would be your best bet. Not a hill you need to die on as it were.
I did find this post on here by another contractor that I found quite informative. Specific to your question would be the part about Part 9 of the IRBC. I'll post it below just for general knowledge purposes. Although, it may help you when dealing with your client convincing them 42" hole depth is fine.
"Unlike another reply I saw... the answer is no. You might not need to go down 4 feet into the soil. It all depends on the location and the type of soil you have. Another factor is the height of the structure. I have been using deck blocks for the better part of 25 years and none have ever moved. The 4 foot requirement is something written into the Ontario and National Building code in part 9. It is intended for a heated buildings or a house.
If you look around, you will see many cottages where the supporting structure is no more than poured concrete slabs underneath piers. It is true that frost will move them about a wee bit, but when the frost leaves, they will go back to their original position.
I have seen many posts that have been set at 4 feet blow the soil which have heaved. This is where unfavourable soil conditions exist. The heaving is caused by a phenomena called Ad-freezing. This happens when frost attaches itself to the sides of the posts and lifts them. Once lifted, they cannot go back down the hole. You have surely seen many fence posts that seemingly 'walked' upwards.
Dow Chemical who are the manufacturers of the Styrofoam* brand of products have researched this in many places across the world. You might want to look at their website and search out 'Soils Insulations'.
If you do choose to go with deck blocks, I highly recommend you use a patio slab underneath it. This inexpensive addition will increase the load bearing capability of the deck block 3 fold and thus prevent any 'settling'. This knowledge I gained from being a past Dow Chemical employee and dealing with architects and engineers who use similar construction methods all over north America."
Fence construction is not addressed in the Building Code (a fence does not meet the definition of a building). The only exception is that a swimming pool needs to be secured by a non-climbable 6' high fence and gate (but again no details regarding construction methods).
It would be a different story if the fence post was supporting something (i.e. carport roof, deck, balcony).
As Tim mentioned I too have witness ad-freezing many times where a concrete pile has lifted over the winter and not re-settled the next summer (commonly houses with walk-out basement and deck off main floor).
Common sense and experience would probably tell you you will be OK, however this could be a contractual dispute & a customer seeking an opportunity to not pay. Perhaps the customer would accept a written warranty?
4ft code is for foundations and footings there is no code for fences , I believe 42 inches of solid concrete is more than sufficient I have never had a bad ost move or heaven before i just was wondering what everyone else thought
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