Would not put a basement in an ADU

Hi Westcoast Hopeful, could you share why you wouldn't do one? thx

In my town, if the first floor grade is within 3 feet above the grade plane, then the basement doesn't account as a story, no sqft will count towards the FAR and you are allowed to have a basement for the ADU

So essentially, an ADU allows you to double (minus staircase) the total area of the ADU? Seems like a smart way to go.

In my town, yes, also the attic is almost free space (as long as under 40% of 2nd floor) and it doesn't count towards FAR either.

I'd do it in any event, but it may, in part, depend on where you are. If your afflurent coastal community is in the northeast you're already needing to dig footers down to a 48" frost line, going a few feet farther to make a full basement is a relatively small upcharge-- and makes installing all the other plumbing, heating, and electrical in the house easier. OTOH, if you need to blast ledge the whole way the cost can become prohibitive.

When we lived in LA we built a guest house with basement. We went extra deep and had 10 ft ceilings in the basement. Steel beams were used to meet earthquake codes. We were required to have large light wells for emergency egress. We handled those by having a longer staircase with a landing 2/3 of the way down that allowed access to one of the egress windows. We split the space into a storage room and game room (pool table, foosball and drum set). We also had a full drain system and sump pump installed. Doesn't rain much in LA, but when it does you get a lot of it in a short time. Never had any water issues. At that time (2011) the cost of adding the basement was an extra $80,000. That was the time when costs were the lowest in LA and RE market started rising after that.

For me I guess I just don’t think I would recoup the added cost of doing it. We have a rental suite, not separate coach house, and we carefully decided every inch of that space to make it cost effective and make sure when we rented it we recouped costs and it was a worthwhile addition.

I think wasting space in the main part for stairs for a space you might use is not a good plan.800 sq ft is not large and staicase take up space

The person that is designing the ADU is probably the best person to answer your question, them and your bank account.

Why go to the extra expense for a basement for an ADU which will only be occupied part-time? On the other hand, will someone be living there full time?

As you're on the top of a hill (rise, knoll, etc.), could the lower level be a garage with outside access only (no internal stairs)? Could also be used for workshop, storage (boats).

It sounds like you don't intend to rent it out, so make it useful to you.

Hi all, thx for your comments. Yes I live in the Northeast.

My area doesn't allow blasting, only allows hammering :-D

@ latifolia if I build a drive way and use the basement as a garage it would destroy the current grade and without the right grade plane I cannot have the 800 sqft living space I wanted.

If zoning and coding allowed for it and I could afford it, then I would do it.