garage structure (beams) 3

[x83camaroz]

I am building a new garage which would like to have a free 24' span. What should I use for the floor joists and what should I use for roof trusses to avoid any center support columns? I could live with a structural wall on the second floor (rooms above) if I had to, but would really like to have an open 24' free span in the garage (first floor) so car work is not impeded by having to work around steel posts. Could someone please tell me what this would require? I'm going to use 2X6 walls for strength and energy conservation (double insulation). Would I be better off with a center "spine" (steel or wood) supporting 12' spans on both sides for the floor? This is my first foray into large construction and any help would be appreciated. I know my way around saws and such well enough, but I'm a piping engineer by trade, so this is new stuff for me.

 

[boo1]

The second floor should be supported by prefab floor trusses (local truss shop) or wood LVL I-Beams (LP, GP ect). These will provide the easiest and cheapest solution.

Software can be downloaded from the web to size the LVL.

http://www.tjm.com/PressReleases/PRNewMicrollamLVL.cfm

http://www.wii.com/StrucjoistDG.pdf

http://www.lpcorp.com/

 

[RockEngineer]

Another thing to think about is your wall loading. If you have joists spanning 24 ft clear span and roof trusses spanning the same direction you are putting a heavy load on two of your exterior walls. You may end up having to use 2x6 on 16" centers instead of 24" center just to take the design compressive load. To load all walls evenly you may want to run your floor joists the opposite direction as your trusses. Of course then you may have increased the load on your garage door header and it needs to be looked at more closely. If you have a large garage door then what happens with support at the ends of the header. If you have a large gas guzzling SUV you want extra wide and extra high doors because it won't fit through a normal 8'x7' garage door. There goes your 4 ft shear wall panels on both sides of the garage door and you are now putting in alternate braced panels with tie down straps, double studs and two rows of nails on 3" centers. Possibly your header going from corner to corner. If you are only 24'x24' and two full stories plus your roof high that's lots of wind load with the building almost as high as it is wide.

How are you using the floor above the garage? Is it just a bonus room for storage and could you get by using attic trusses and loosing 5 ft on each side?

Isn't engineering fun? One change or question has a domino effect. Even a thing as simple as a garage with an room above can cause lots of thought.

Good Luck. Keep asking yourself questions so you don't run into trouble. An inquisitive mind is a terrible thing to waste.

 

[Trussdoc]

Another consideration (just to add to the fun!) is where to put the stairs to the attic. Unless you want just a pulldown stair that will fit between joists, you will have to consider some headers and a girder, or posts, to support the stairway opening.