Replies

1. 
   walta100 | Oct 16, 2021 08:34pm | #1

   If you wait tell spring understand concrete take 3 or 4 weeks to reach strength that will support your new home.

   I do not know what the risks are should the ground freeze below your footing some of the risks may be better understood by your local people as they will understand the local conditions best.

   Walta

1. 
   Malcolm_Taylor | Oct 16, 2021 09:21pm | #2

   Concrete toughens up pretty quickly. It varies by mix but typically you get something like:
   3 days - 50%
   7 days - 65 to 68%
   14 days - 85 to 90%
   28 days - 100%

   We strip the forms 48 hours after p0uring and start framing a couple of days later. The only thing we are cautious around are tall walls getting backfilled.

   As Walter said, the risk of having the ground around a new foundation freezing depends a lot on what's underneath. A walkout basement is pretty hard to insulate temporarily. I'd lean towards waiting until spring.

2. Expert Member
   Michael Maines | Oct 17, 2021 10:50am | #3

   I have seen daylight basements in southern Maine heave with frost when not enclosed before winter. But those were not built with proper frost protection. Do you have frost-resistant details, or is your foundation design dependent on a heated interior to keep the ground from freezing? (Which is not a code-compliant approach, but very common for walk-out basements.)

1. 
   Malcolm_Taylor | Oct 17, 2021 11:31am | #5

   Michael,

   Isn't even a code compliant basement where the footings are installed deep enough to meet local frost level requirements still at risk of frost heave from the interior before the building above is completed?

1. Expert Member
   Michael Maines | Oct 17, 2021 12:50pm | #6

   Malcolm, good question and I don't have a good answer. I know that frost will extend deeper than the frost line we design to. When designing frost-protected shallow foundations there are different rules for heated vs. unheated buildings. But for foundations that extend below the frost line, there are not different requirements for heated vs. unheated buildings so I believe it should be safe from heaving, especially if there is also sub-slab insulation installed.

3. 
   drewintoledo | Oct 17, 2021 11:19am | #4

   I was thinking about doing the same; adding the decking and a sump pump on an extension and then covering with something like this: https://www.reefindustries.com/under-slab-vapor-retarders.php
   You can purchase up to 200' x 200' seamless material. If the UV wouldn't kill it, I'd move it to my under slab barrier when the builders were ready to frame.

4. 
   17whippoorwill | Oct 31, 2021 02:15pm | #7

   Thanks for all your input.

   It seems the foundation will be on 'ledge', which, according to our 30+ experienced builder (not building-science experienced), is not effected or does not incur frost heaves. I've rocked his boat with questions for more than a year, so I'll have to simply let it go. The good news is that based on the current progress, I would wager there is no way he'll excavate, no less pour it until spring.

1. 
   dfvellone | Nov 01, 2021 10:49am | #8

   I poured my monolithic slab-on-grade in mid November in zone 6 (upstate NY.) Like you, bedrock was very shallow, and I had also installed a substantial crushed stone base with ample drainage. Effectively, there was nothing to heave.
   Pouring concrete in freezing weather poses some challenges, but with the use of heated water and an accelerator you can do it, although at increased cost. I'd wait until spring unless it absolutely has to happen now, and I absolutely wouldn't pour in the deep cold of winter.

5. 
   krom | Nov 01, 2021 08:01pm | #9

   Helped a friend a few years back, who's modular didn't arrive on time.
   The walkout basement was poured late in the year, and by time the house got there it was too late, the ground had heaved and raised some of foundation several inches, cracking above a door.
   Without a house above it, or backfill against it, you are pouring the footer on the surface, even if it will be 10' below grade when done

6. 
   arnoldk | Nov 03, 2021 09:54am | #10

   I will be pouring my slab on grade shortly where temperature are dipping just below freezing at night. I have been ensured that it's possible and there should not be any issues but it does cost more due to the additives and the type of concrete they need to use.

   I do want to point out that both our house and detached garage will have a frost protection skirt 4 feet out from the footing and insulation under the entire slab. We're moving ahead because I want to get this project moving and plan on building through the winter.

   Arnold