Expert: Bruce E. Johnson - 4/7/2009

Question
I'm thinking about building a 30x40 garage on some land and
use it occasionally as a weekend shelter to sleep.  The
idea was to build a 2 car garage with an attached heated
finished area to sleep in.  10 years from now, when I can
spend more than a few weekends a year there, build a house
next to it.  A 30' x 16' part of it would be sheet rocked
and some type of flooring put down.  Probably build a
closet and a bathroom for a composting toilet (now sewer or
running water).  Add some cabinets and a sink for filleting
fish.  When the house bets build, it could be a guest house
or converted to a workshop.  I can't find anything in the
building codes, but thought there was something about
living space and garage floors from being on the same
level.  The was separating the garage from sleeping space
would be 5/8 fire rated sheet rock on the garage side with
a fire rated door.  Most the construction here in northern
Wisconsin is with a frost foundation or full basement.  Are
there any problems or safety concerns with having an
attached living space and a garage all on one slab-on
grade?  Thanks in advance!

Answer
Hi Chris, different states and counties have differing codes on this.  In some places it is 8" but you can get by with 4" at one end and slope your garage the other 4".  In some places it is a full 8" step.  If my memory serves me, it has to do with fumes from automobiles that are heavier than air and collect along the floor.  These fumes build up and could cause health problems and in some cases death.  The step is an added precaution.  Some places require a vent in the garage also for this reason.  The only way to know what is required in your area is to ask.  You can probably get a permit for your garage with an attached bathroom and even a kitchenette without having to say whether or not you were going to live there.  Your building codes will also tell you what kind of foundation you can get by with.  You still might need to dig down three feet for your foundation to get below the frost line and then cap your foundation wall with your slab or do a floating slab inside your foundation. I hope this information helps feel free to write again regarding this or other matters, sincerely bruce e johnson..bejohnsonconsulting.com