Expert: Bruce E. Johnson - 3/21/2009

Question
QUESTION: Hey Bruce- I am talking with contractors about an addition to my house.  I
live in a flood plane in FLA and I was hoping to build a two story addition.  
My house is stem wall construction but one quote I received was monolithic
slab addition.   I think stem wall might be better in my area.  I would have
poured concrete within the stem wall not wood floor.  how much more
expensive is stem wall and is it worth it?  Thanks for any help.
Jim

ANSWER: Hi Jim, I am a big proponent of monolithic slabs whenever they are possible.  It is a much simpler and generally less expensive foundation.  Think about it.  One step and your foundation and slab are poured and ready to go.  With a stem wall, you pour the footing then install the masonry, then pour the wall, then grade inside the foundation wall, then pour your slab. One factor that may encourage a stem wall foundation would be the finish floor elevation requirement.  If the flood plane finish floor requirement is higher than your existing floor then you would almost need to do a stem wall foundation. Or if your lot is small and to raise the elevation of the slab requires a bunch of fill and you don't have enough room to taper the fill in such a way as to discourage erosion then you may need to go with a stem wall to retain the elevated dirt.  Structurally both methods are acceptable in Florida.  I hope this information helps feel free to write again regarding this or other matters, sincerely bruce e johnson..bejohnsonconsulting.com

---------- FOLLOW-UP ----------

QUESTION: Thanks Bruce- I appreciate your quick response.  I can also see the advantages from your (the builder's) perspective in time and money.  But if time and money were not factors, structurally speaking, are they equally strong?  You say they are both acceptable in FLA.  But I lived through hurricanes in south FL - I want the strongest. (by the way - money is always a factor - I'm speaking hypohetically).  Again, I really appreciate your time and knowledge.
JIM

Answer
Hi again Jim, I see no advantage to using a full blown foundation over monolithic slab structurally speaking or otherwise.  I have built some pretty big buildings using monolithic slabs in Florida and they are all still standing...If your soil conditions demand a deeper footing placement then yes you will need to go with a stem wall and footing but otherwise, as mentioned before, I will use and have used both types of foundations for similar buildings with no difference in structural performance that I know of.  I hope this information helps feel free to write again regarding this or other matters, sincerely bruce e johnson..bejohnsonconsulting.com