Foundation fix ideas

[Acadian]

I live in Canada. This past year was especially cold.

There is an addition to my house that was built on top of cement post (instead of a full foundation) by a previous owner. This past winter it appears that the frost line went deeper than usual which caused one of these concrete post to lift. As a result, I have some small cracks in my plaster walls and my patio door was ajar (unable to close) for most of the winter (letting the freezing air come in). With the warm weather, my door has settled back down (although I can't close it enough to use the lock mechanism).

I got some quotes from foundation companies to pour a new foundation under the addition. It would cost me $20,000+ (it's a 7' x 12' area) and they will need to tie in to the existing weeping tile. If these weeping tiles need to be replace (I have minor water issues in my unfinished basement), the cost goes up to $50,000+.

I'm not convinced that it is worth the cost to do this project. I'm wondering if there are any more mustashian options that I could consider. If these alternative options don't work then I could look at getting the foundation poured. However, living on a single income, this would delay any hopes of FIRE by many years. Based on current plans, I would probably stay in this house another 15 years. At that point, if I reach FIRE, I would sell and move to another city. Alternatively, if my life circumstances change (I meet someone and decide to move), I could sell sooner.

I would appreciate any thoughts you might have.

[zolotiyeruki]

This is a totally uninformed question, but could you pull out the existing post, dig a deeper hole and pour a deeper post?

[Milspecstache]

IF you are happy with it as is and only concerned about it moving again...

Then there are ways to minimize the frost depth.  For instance, you can dig down around this foundation and bury sheets of foam insulation.  It should be higher next to the house and deeper as you go further away.  This creates a cup which traps the earth's heat around your foundation and slows down the rate at which it can cool and therefore freeze.

This is known as frost protected insulated footings.  Try googling it.  One link:
http://www.renovation-headquarters.com/foundations-14.htm#.U6z-8Cjw9co
Look at figure 18.

This would be a minimal cost MMM solution that would give adequate results I believe.

[Acadian]

@zolotiyeruki
This is certainly an option. The difficult part is that (as opposed to a deck that can be removed) the house is already sitting on top of these posts. This makes it difficult to remove the existing post as I have to support the house and find a way to dig without having the room to use larger equipment (like a mini-excavator). There is about a 2 1/2 foot clearance between the ground and bottom of the addition.

@Milspecstache
Interesting idea! I was thinking of 1) sloping the ground away from the foundation to minimize water accumulation 2) Closing off the space underneath the addition by adding walls (maybe plywood with a layer of hard foam insulation on the inside) and 3) maybe laying an insulator on the ground directly (like hay) to try and slow down the frost from going as far down. Perhaps I could also add the footings in the link you provided.

[Greg]

There are 2 ways frost can move a post/pier.  One way is frost gets under the footing or end of the post and pushes it up as the frost expands the ground underneath it.  Another way is the ground freezes to the post/pier sides and pulls it up while it expands.

So, you may be able to expose the sides of your post/pier and cover it with something slippery like 2 layers of plastic to frost depth, even if you can't get under the footing.

Another thing to look at is where any water comes from, like the roof gutters.  The less water in the ground the less frost heaving will occur.

Hope that helps.

[ProfWinkie]

+1 Greg