I am beginning to build an addition that will become a family room and the first step will be to install footers. I checked with the code department and told him I would go 36 inches deep and 16 inches wide, and he replied that the 36 inches is fine but I must go 20 inches wide and 8 inches thick. He lost me with the 8 inches thick because I thought the thickness is the 36 inches. Could someone explain that to me? Thank you.

Rich

 

I think you confused the foundation stem wall and footer terminology.
This may help. The footer/footing is positioned below the stem wall to spread the load over a wider area in order to prevent settling. Part of the purpose is to reduce the amount of material needed in the wall itself. Also, a poured footing allows you to use CMUs (Concrete Masonry Units, also often called "Cinder Blocks") for the stem wall.

The required width of the footing is a function of the type of soil and type of construction. Other than a soils engineer, your building department is the best source for that type of information.

Lastly, don't skimp on the steel reinforcement ("rebar"). There should be at least two continuous strands throughout the footing. Because this is an addition, you will want to drill into the existing footing and insert the ends of the rebar to provide vertical support in order to keep everything at the same level after you're done.

 

You're thinking of the wall - the footer is what the wall sits on, as Doug's drawing shows.

 

The thing to verify with the building department is how far below your final grade level do they require you to be with the bottom of your footing. Does the building department require the bottom of the wall to be 36" below grade and then the bottom of the footing another 8" below that (44" below grade) or does the bottom of the footing have to be at 36" below grade. The more excavation you do the more dirt you have to pay to remove, haul away, stockpile & backfill, etc. The extra 8" could increase your excavation depth by 15% to 20% which could be substantial. Of course your have to get below the frost line if you are in an area subject to freeze/thaw issues so this may determine the required depth for you. Doug's drawing illustrates the detail fairly well. The only thing I would add is a keyway in the footing to allow the foundation (stem) wall to lock into the footing. The keyway is typically created by placing a 2x4 in the center of the footing and then removing it after the footing sets up. This notch (keyway) allows the wall to tie the two together.

 

we made our keyways like looped off pyramids but was in the days of batter boards,termite sheilds and such do they still do that?

 

Going to do an addition myself. The drawing is very good on details. Was wondering what is the purpose of the sill insulation and what kind of material would you use for that? Thanks.

 

Sill insulation is somewhat of an air barier between the concrete and wood. It comes in rolls and is ridged along it's length.