Have you ever walked into a basement and immediately noticed that there is what appears to be a wall built in front of the foundation wall, which looks like a ledge wall around the interior perimeter of the basement? Many homebuyers are immediately puzzled by this type of altered foundation, and wonder why the extra wall was integrated into the structure.
The following photos, from our past inspections, portray altered foundations on homes built pre-1930's.
1. 'MICHIGAN STYLE BASEMENTS'
We will begin by touching base on a common type of foundation throughout the Midwest found on homes built pre-1950's. The photos above are portraying what is known as 'A Michigan Style Basement'. Michigan basements are typically shallow and have a low ceiling height compared to standard basements. They are often used for storage or utility purposes rather than as livable space. The term Michigan basement is believed to have originated due to the prevalence of this particular style of basement construction in Michigan. It is not a technical or official construction term, and can be referred to by other names.
WHAT IS A MICHIGAN BASEMENT?
A Michigan basement is a former crawlspace that has been dug out, generally to a depth of 5 to 7 feet to allow for a basement. During construction of these perimeter ledge walls, the excavation typically begins approximately 2 feet in from the inside of the existing foundation walls in order to preserve the soundness of the existing foundation walls and footings. This retaining wall may be comprised of brick, poured concrete or CMU block. The crawlspace footings are covered by the wall which creates the shelf or ledge, which acts as a retaining wall against the soil under the original foundation. The center of the crawl space inside this ledge is excavated, creating a basement portion. The ledge walls are usually about 3 feet below the ceiling, and sometimes slope towards the center of the room.
To sum it up, Michigan style basements are simply a crawlspace converted into a basement, and are common throughout the Midwest.
MICHIGAN BASEMENT WITH EXISTING CRAWLSPACE
When a crawlspace is converted into a basement it is not uncommon to find that only a portion of the crawlspace was converted which creates a dual crawlspace/basement foundation.
The following photos from one of our past inspections shows the crawlspace portion of the foundation and the Michigan basement portion of the foundation.
2. BENCH FOOTING
What if the wall appears to be shorter than a Michigan basement ledge wall? In this case you are likely looking at bench footing.
Basement benching (aka bench-footing) is a method for adding height to an existing basement. Instead of excavating under the existing basement foundation, a bench or ledge is built around the inside perimeter of the existing walls, allowing a new concrete slab to be poured at a lower depth without modifying the foundation walls or disrupting the bearing capacity of the soil. The most outstanding drawback to bench-footing is that it takes away from the square footage of the basement because of the fact that you have this new bench around the inside perimeter of the basement.
3. REINFORCEMENT
Lastly, foundation walls in older homes that have been subject to lateral pressures leading to displacement or bulging were sometimes buttressed by a new wall to prevent further foundation failure. Buttressing may have also been used as a precautionary measure.
In conclusion, a ledge/shelf or bench wall built in front of an original foundation wall is an altered type of foundation which can have several reasons for its construction, some of which are included in this blog. We have written this blog to provide valuable information for homeowners, homebuyers and real estate agents. These added walls are subject to the same types of failure any other foundation wall is i.e., cracking, displacement, moisture intrusion, etc. Any wall showing signs of failure or structural movement are recommended to be evaluated by a local foundation specialist. Thanks for reading... until next time!
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