new second floor

huangyhg

new second floor
hello,
i am doing a residential design/build project where we are adding a second floor to an existing split-leve house. the addition is above an existing 4-car garage that is 27'x33' with 8' clg. ht. and pre-fab roof trusses.
my question is this, what sort of a floor system should i use? i am thinking of using 16" wood i-beams, but since their max. span is about 21' that requires me to have a bearing wall in the center, but i don't know what size lvl beam to spec. also, those lvl beams will be expensive, and the homeowner will freak when i tell them how much they cost.
any other ideas of accomplishing this task?
thanks!!
use more 16" beams than you planned on. hire an engineer.
haynewp is right, hire an engineer. if the homeowner "freaks" about the cost of the engineer, replace the existing homeowner immediately with a fly-rod.
-mike
realise that after hiring an engineer, he may require you to strengthen/underpin existing foundation below the new addition (or conclude that it is not possible).  most homeowners only think of cost associated with what's "visible".  existing foundation may not have been designed to carry the additional floor loads.
jrtm76,
a 24" deep open web floor truss spaced at 24" o.c. without any additional roof loads would clear span the 27'-0" without any additional load bearing requirements in the center as long as the floor loading is 40#psf live and 15#psf dead.
contact your local truss manufacturer, they will normally provide you with all of the truss layouts and engineering requirements as part of the selling price for the trusses. the cost should be about $95 each...
thank you guys for all the suggestions.
i contacted a local truss designer and they are suggesting a 20" deep open web truss at 19.2" o.c.
there is actually an engineer looking at the foundation today, he already suggested we reinforce it and the homeowner has agreed to it.
again, thank you all.
another concern you should have in addition to having floor joints that will support the design loads, you should also consider if the existing footing will support the new loads.
yes, that has been considered and a structural engineer was hired to design reinforcement to the existing footings.
i am in the process of pricing two ways to add a second floor to a family house that has million dollar views (from the roof).  since my husband has built butler buildings cheaply in our citrus groves, i asked several metal building companies to give me a price on adding a second floor around and over the existing house.
of course the first floor roof will have to be removed and covered while the second floor structure goes in, but the prices are much much less from the metal building companies.  oh, and before you gag, realize that you can clad a metal building in any finishes you want and make it look just like any residence.
oh, and a metal building can be built in 7 days.  this is a lot quicker than conventional construction which adds months and frustration.  i will keep you posted...we are considering filming the project and submitting to this old house...
i don't like pre-engineered metal buildings personally.  they aren't in it to supply a good quality structure imho.  they want to sell metal.  always re  
i've also had some bad experiences with pre-engineered buildings.  they have much higher allowable deflection and drift limits than typically would be used for good design.  the cost numbers always sound more attractive becuse you are getting far from a complete package...i always hear their advertisements on the radio and wonder how many people sign up not knowing that glazing, foundations, finishes and hvac are not included...