How Many Subbasements Can a Residential Dwelling Have?

This is kind of a half-serious question, and I suppose I could have put it in MPSIMS. But it is partly a factual question, so I thought it would go good here.

I suppose we all think about a dream house we would love to live in, and I am no exception to this. As I’ve said a while back, my father and I are happy living were we are presently. It’s a nice and fairly large house. But ever since I was a kid, I thought it would be neat to have a third story on your residential house. In older homes, these are usually called attics, and are small in comparison to the rest of the house. But recently I thought of something interesting. I assume three stories must be the most stories allowed by zoning codes (I certainly have never seen a four-story [middle-class] residential home–have you?). But what about basements below basements, that is subbasements? Since these don’t upset the general look of the neighborhood, it seems that they must be allowed.

But exactly how many are allowed by law? And for that matter, are their any practical considerations for how many you can have (underground sewage pipes, for example)? And while where at it, how many subbasements can any building have by law, and by the laws of nature? Probably almost no end, I’m guessing. But my main question, as I’ve said, concerns residential areas, and the laws that (generally) apply to them nationally.

As I’ve said, I am not planning on building such a house presently (i.e., with an attic and subbasement). But who knows, if I win the lottery, I may reconsider;).


Jim, I will wade in a little bit on your questions (not a lot!)

Couple things I think… depth of basements, from a zoning standpoint, probably are governed by … structural thinking. If, say, you wanted 4 living stories below ground, building officials are going to want to see that it will hold. That is, no chance of cave-ins or water seepage to hurt the thing. Also, ventilation to lower floors is important.

Access is another. Building codes dictate emergency ingress/egress. Example: there is (are?) a certain amount of windows one must have for emergency ingress/egress. This would be limited underground.

One other item: basements are not usually permitted in floodplain areas. Exceptions can be made with proper sump pumps etc.

If one is serious, I would think a frank talk with the building official will make clear what is allowed and what is not.

The majority of zoning codes in the United States have a maximum height of 35’ for single family houses. Zoning codes in Canada often have maximum house heights of 10.6 meters, which is … about 35 feet. I don’t know where the 35’ came from, but it’s there.

Anyhow, zoning regulations usually don’t consider basement floorspace as a part of the gross floor area of a house. Building codes, however, will apply. You’re limited by geology, and the existence of subsurface rights others may hold to your property.

Building codes require workign, effective drains in basement floors. Most basement drains lead to a deeper sanitary or torm sewer, or on rare occasions, very permeable soil with positive results from a perc test. You might need a way to pump water that collects on the lowest basement floor back up to sewer or street level. If the power goes and there’s a pipe break or flood, the structural integrity of the building will be significantly hurt.

I don’t know depths specifically but i can give an example of a subbasement. Here in Carroll Co., MD there is a rather rich family and i used to be friends with the kids. They have a normal basement, then, under the normal basement they have a racquetball court. So i guess it can be done.

will you also be installing a BatComputer down there? :smiley:

No, it’s to keep his cask of amontillado.