Frost line question


  #1  
Old 05-15-12, 10:20 AM
M
Member
Thread Starter
Join Date: Jan 2008
Location: West of Chicago
Posts: 307
Upvotes: 0
Received 1 Upvote on 1 Post
Frost line question

I live just outside of Chicago in the midwest. I am digging to install a couple footing to repair my porch. When digging one of the holes I came across my water line at about 36" or so. I had to move this hole over a couple feet but no problem there.

They say the footer depth needs to be 42" due to our frost line. Why is the water line only down 36"

Another issue is where exactly to start measuring... Actual ground level? What about loose ,like, potting dirt along the side of the house? Should this be counted or not?

We dug a trench for a foundation wall (just a porch). Is this suffecent or do I need to form a wider footing below this 8" thick wall? We plan to pour the mix directly into the trench and holes.
 
  #2  
Old 05-15-12, 01:06 PM
badeyeben's Avatar
Member
Join Date: Dec 2006
Location: Southern ILLINOIS
Posts: 1,194
Received 61 Upvotes on 55 Posts
According to the map of frost depth in Illinois that I have you in Cook county show frost depth at 25 to 30 inches. so anything over 30 inches deep should be fine. They probably had a trencher with a 36 inch bar so that is why the water line is that depth. That way they do not have to measure just put it all the way down!
 
  #3  
Old 05-15-12, 01:31 PM
Join Date: Mar 2005
Location: USA
Posts: 5,650
Received 1 Upvote on 1 Post
The frost depth for structures is an average MAXIMUM depth to protect long term structures from heaving and frost damage. I was in an area in northern MN that had about a of month or two with average daily minimums of -10F to -30F and found areas with good/reasonable snow cover that had only 6"-8" of frost penetration because of the snow cover. Driveways and sidewalks that are clean do not insulate the ground or contain the natural thermal heat storage, so the frost can be deeper there.

When it comes to utilities, they are not really permanent of possible to economically locate then deep enough. I lived in northern MI where the snowfall was typically 100"-200", but the rock was at 4' or less. The utility required everyone to run a trickle of water from the lowest tap and reduced the water rates in the winter because it was cheaper from an economic standpoint since digging utilities up is not cheap. The reasonably warm water and the constant flow prevented problems.

I would imagine that septic systems also provide heat from the chemical process.

Where I am now the frost depth is 48"+, but the average soil temperature is about 53F-55F in the winter, so people consistently over-insulate basements since they look at the outdoor AIR TEMPERATURE and stupidly assume they need as much insulation below grade (which is warmer) and then end up paying more for AC in the summer if the basement is a conditioned space with returns.

Dick
 
  #4  
Old 05-15-12, 09:55 PM
BridgeMan45's Avatar
Member
Join Date: Oct 2011
Location: USA
Posts: 2,838
Upvotes: 0
Received 2 Upvotes on 2 Posts
Why are you building a foundation wall if it's only a porch? Wouldn't individual footings (using Sonotubes) be a lot less work and accomplish what's needed?
 
  #5  
Old 05-16-12, 04:45 AM
M
Member
Thread Starter
Join Date: Jan 2008
Location: West of Chicago
Posts: 307
Upvotes: 0
Received 1 Upvote on 1 Post
Yes. Yes it would. You know how this all goes.... 100 yr old house and a surprise around every corner! lol.

I started with a couple tubes under the porch to re- support it. But then got to replacing rotted wood and didn't want to lay a new sole plate on uneven busted concrete. That was only about 8" deep. So we started digging... and digging... and digging. So one edge of the porch now has a trench wall under it. And if we end up doing more under the rest of the porch (it runs the full width of the house, but only one corner sank) we will be drilling with an auger from the outside at an angle. Then clean it up and put a tube at the top.

Its a heck of a project with alot of ins and outs, alot of what- have- you and so forth. lol.No Beer 4U
 
 

Thread Tools
Search this Thread
 
Ask a Question
Question Title:
Description: