Frost depth for remodel?

[COEngineeer]

I have a basement where the owner wants to excavate right next to it, put retain the soil and put sliding door and make it a walk out basement. My question is, now that we excavate the soil and put a new door, I am pretty sure the footing is right underneath the slab. What step do I need to take? The frost depth is suppose to be 3' but now this part of the foundation will only have less than 1'. Please advise. Thanks!

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Sea Water Intake and Jetty Construction

 

[MiketheEngineer]

While technically not correct - if it is a heated basement and the door width not too large say 4' or 5' - you will probably be OK.

Check with your local building official. They may be of some help.

You might dig down and insulate the footing with a couple of inches of rigid foam. That will help.

 

[oldestguy]

Chances are you need to do something to protect against frost heave.

The pink stuff is closed cell and stays useful for insulating. However, you can do less work (than noted above) and make it work.

Excavate down say a foot or so out in front of the doorway, say 2 to 4 feet, prefer four feet. Place the foam horizontally and then backfill on top of that. The vertical face of the footing edge should also be protected from cold with a vertical chunk of the foam.

This stuff deteriorates with sunlight on it, so don't leave it exposed to light.

At this job will you have pontial ponding of rain water at this entrance? You may need a drain system or at least a dry well.

 

[concretemasonry]

There is a system called "shallow insulation systems" (or something similar) using extruded polystyrene in the 2006 IRC.

This could be an economical method to solve the potential problem of frost pentration under the sliding door.

Usually, code frost depths in codes are somewhat overstated, but some situations like the north side of a structure with no snow cover and some traffic, the frost can go quite deep.