Footing Depth for garage

by Dave
(Post Falls, ID)

Question:

I live in North Idaho and believe it is in zone 5. How deep do the footings have to go below grade on an attached garage? If I have 4' stem walls with 2' of the stem wall above the grade line, the bottom of my footing would be 2'-8" below grade. Is that enough?

Thank you for your help,

Dave

Answer:

Hi Dave, thanks for visiting. Sorry for slow response.

Footings depth are determined by local building officials. The city building department where you get your building permit will provide you the information regarding footing depth. They have developed maps for homes and buildings where certain depth is recommended based on climatic factors.

Usually you call them and provide them with your address and they will tell you how deep below grade your bottom of footings need to be. This will be one of the things the building inspector will check when he/she arrives for footing inspection prior to the pour. Footing depth and setback requirements from all sides of property are very critical early on in construction, both are important to be verified by the inspector.

The way you described your footings, 8" thick with 4 ft stem wall sounds pretty good.

One thing to watch for when attaching an addition or garage to an existing structure is to make sure the new bottom of footing match the existing bottom of footings. This will prevent/minimize footing settlements. Make sure to drill and epoxy dowls to match new footings & foundations reinforcements into the existing house.

Since back filling of footing excavations are not required to be inspected, a lot of bio-degradable material are buried and in most cases not effectively compacted.

By making the new footings bottom elevation match the existing will eliminate the chances of constructing above a poorly compacted fill or bad fill material.

Hope this help
Tonga