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Discussion Starter · #1 ·
Hello,

Hoping for some help on options for a ground level deck that won't heave with the frost. I want to build a 12 X 24 wood deck about 6" off the ground. Plans include step down to fire pit etc.. My issue is if it'll work due to heavy clay soil that heaves during the winter. I'm in norther Ontario and frost depth is 60"

Option 1: Was going to drop some of those big foundation screws but I'm scarred that if the deck is anchored that close to the ground and underneath heaves that it'll rip it right off the screw. Same would occur if I use cement pillars.

Option 2 - Sitting on the ground on cement footing blocks. Figure this will heave like crazy. How deep would I have to excavate and how many inches of gravel base would be required to stop heaving. If this is close to the house will gravel filled hole surrounded by clay soil become a swimming pool of water...

What are people doing and is there an option I am missing?
 

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Master General ReEngineer
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I want to build a 12 X 24 wood deck about 6" off the ground. Plans include step down to fire pit etc..
Ayuh,...... A standard step is 6/ 7",.....

Are you sayin' yer yard rises more than 7" in the winter,..??

I'd use sonotubes, at least 60" deep,.....
 

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Discussion Starter · #4 ·
Well if I use 2x6 framing then I only have 1"-2" space below before the high becomes too high for no additional step. So yes the heave is what I'm trying to mitigate so I can keep it within those parameters. Just not sure if it's possible or how to do so
 

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retired framer
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Well if I use 2x6 framing then I only have 1"-2" space below before the high becomes too high for no additional step. So yes the heave is what I'm trying to mitigate so I can keep it within those parameters. Just not sure if it's possible or how to do so
Do you know if you have a perimeter drain at the footing?
 

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retired framer
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I would scrape off 2 feet of soil and replace it with compacted gravel and pour concrete with a gap to the house so it can move a little if it wants to.
 

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Discussion Starter · #8 ·
I would scrape off 2 feet of soil and replace it with compacted gravel and pour concrete with a gap to the house so it can move a little if it wants to.
Thank Nealtw.. How much concrete would you put?
Is 2 Feet good even if the frost goes down past 5 feet?
I guess the concrete would eliminate my worry or the hole holding water.
Really appreciate the help.
 

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retired framer
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Thank Nealtw.. How much concrete would you put?
Is 2 Feet good even if the frost goes down past 5 feet?
I guess the concrete would eliminate my worry or the hole holding water.
Really appreciate the help.
No the concrete would be a slab, 4 or 5 inches, your only real protection would be to replace all the clay with with soil that does not expand or freeze.
 

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Usually Confused
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If you have a local contractor that installs screw-piles, ask them. I'm not sure you would have enough clearance for the saddles on top of the piles but I'm not that familiar with them. I would consider either screw-piles of sonotubes down below frost on a floating deck (no ledger) rather than a concrete pad.
 

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I know you stated that you want a ground level deck that won't heave with the frost. However, have you considered that it might be okay to build a deck that heaves with the frost?
If designed correctly, it will heave uniformly and not end up wavy.

See my prior post for pics of my low deck without frost footings:
https://www.diychatroom.com/f19/replace-deck-need-some-direction-683775/

You might be able to use 4x6 grade beams (joists) on 24" centers, oriented perpendicular to your house, and deck it with 2x6 treated lumber, for example.
Of course, your city might forbid this type of construction, but it never hurts to ask.
 

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Usually Confused
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lenaitch's helical pile suggestion is good, but you probably should check with your local approval organization (county?) that they will allow them.

I was assuming that's what the OP meant by "big foundation screws" in Option 1. Depending on local building code, he might not even need a permit for a low deck, but we don't know that. As far as I know, it is not a DIY job unless a rental shop stocks the necessary power driver, which I have not seen. I assumed by considering the option that he knows he has a local contractor.
The real issue with frost jacking isn't the surface of the ground hitting the bottom of the structure; that will usually settle back down and has the ability to dissipate because, well, it's on the surface. The big issue is the expanding soil pushing up posts and the posts not settling back, or solid surfaces being impacted unevenly and breaking. For posts, I have seen simple mitigation measures as wrapping them in poly and/or backfilling the hole with sand.
 
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