Expert: Dan Griffin - 6/2/2008

Question
30' trailer on graded lot w/ slope behind and in front. I would like to add large common room and deck ( 26' X 24' ) to front and cover entire camp with trussed roof. What dia. concrete footers do I need. I know this is sort of vague, but I am just starting to research and plan for near future construction. Thanks, Tim.

Answer
It is a bit unclear to me what you are planning.  A common room tied into the structure of the original should have its own footing that works with the original trailer footing system.  The deck needs an independent system and the roof system needs its own.  Elements of all three can be combined, but look at the design and issues as separate items.

The common room should be designed for 30 to 40 #/SF live load, snow load, and wind load.
The deck should be designed for a minimum of 40 #/SF plus the common snow load for your area.
The over-roof needs to be designed for Snow, wind, uplift, seismic (if required).  Roof requires a very minimal live load and dead load but the uplift and wind loads are substantial.  Bracing for shear will require some type of engineering.  If you have a local truss manufacturer, contact them for design ideas and input.

I think your roof will work best with steel columns, but will still require a moment frame design for wind shear.  The deck can be done with treated lumber in concrete piers, though I don't like to do them that way.

I don't feel like I answered your question, but I can't without much more information and the answer really needs to involve a structural engineer in your area.