I have a building that I'm converting into living space for rental units. The building is on a cement slab foundation and to bring it up to code, I need to install foam board insulation around the entire exterior perimeter of the slab 3 feet deep.

My issue is I'm not sure what is the best/safest way to dig around the entire perimeter of the building.

  • Is it feasible to dig it by hand?
  • Is it dangerous for me to excavate the entire perimeter at once?
  • Are there any tools than could help with the job?

I considered an excavator, however, one entire wall of the building is covered by an awning, which wouldn't allow for the excavator. There is also some cement I will have to bust away to get to the dirt.

Any advice would be helpful.

1 Answer 1


Who told you that you need insulation 3’ down around the perimeter of the building? Let’s try this a different way:

The Building Code is divided into several sections, including the Energy Code, Structural Code, Fire Code, etc. Your question references the Energy Code.

The Energy Code identifies the minimum energy code requirements. These requirements are outlined in what the Code defines as the “Prescriptive Path”. That is to say, if you use the minimum values of each item in the Prescriptive Path, (i.e.: R-value of insulation in attic and walls, U-value for windows and doors, efficiency of heating units, etc.) then you comply with the Energy Code.

However, you can substitute a higher value for one item in order to reduce (or eliminate) another item.

So, if you don’t have perimeter insulation 3’ down around your slab, you may be able to increase the R-value of your attic insulation or purchase a more energy efficient heating unit, etc.

In order to change the items in the Prescriptive Path you’ll need to hire an architect or mechanical engineer, but they could save you $$$$ and a ton of grief.

Btw, I noticed that you’re converting a building into “residential units”. If the building will have more than 2 units, you’ll need fire sprinklers, unless you install a 2-hour fire wall between each 2 units. (An architect can outline how to do that.)

  • I'm using the program RESCheck to determine where I need insulation. Unfortunately, the previous owner built the second floor with 2x4 exterior walls and only used R-13 insulation. I either have to rip all the dry wall out, and build out the walls to have R-19 or add insulation to the perimeter. Jun 17, 2020 at 18:09
  • @GaryHoliday I don’t think ResCheck will allow you to substitute a higher attic insulation value or higher efficiency heating system. Try the commercial version: ComCheck...I think it’s called.
    – Lee Sam
    Jun 18, 2020 at 17:17

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