definition of "shelf foundation"

[BubbaJ]

I recently reviewed a shelf foundation in a residence built in 1900 where part of a foundation wall had collapsed due to flooding.

There were no stones or rock visible in the debris, only earth and the thick cementitious slurry top coat.

Does anyone have experience or knowledge of this type of foundation system? Also, is a "Michigan basement" the same thing?

 

[msquared48]

Never heard of the term, but it makes me think if this is a colloquialism for a Raft or Mat foundation we refer to today, or a variation thereof.

Thinking further, it would make sense to install this kind of foundation in a known flood plain that probably had poor bearing soils.

Mike McCann
MMC Engineering

 

[BubbaJ]

Nope, not a mat foundation.
It is a foundation wall that is usually 5feet tall or so, then rounds out at the top to "level", where two or three courses of CMU are set back from the face of the foundation wall. Thus forming a "shelf". I have seen it in a lot of homes circa the 1900s.
I found one resource that described a "michigan basement" as a thick wall of rock & gravel retrieved from the basement dig, then covered in a cementitious slurry as a waterproofing measure. I wondered if that was the same as a "shelf basement" and if anyone had additional resources on the construction method.

 

[msquared48]

That 5' high wall looks like it has a batter to it too.

Mike McCann
MMC Engineering

 

[BubbaJ]

This one has a small angle to the vertical face. I have seen others with much more slope.

 

[aeoliantexan]

I think a lot of these developed when a basement was added some time after construction. The perimeter foundation wall was shallow, and the shelf was left to avoid undermining the foundation. My daughter's house in Iowa is similar. In her case, the inner basement wall is a single width of bricks. It just keeps the slope from ravelling, doesnt support it.

The approach depends on the soil being cohesive and remaining unsaturated. Poor drainage, a bad gutter and a downpour can bring it down.