residential floor joist beam possibilities

[tonyv11]

"Can a structural engineer please help me with this problem". I need to remove a load bearing wall to expand a living room on the first floor of residence. I am also building a second story on this home. I need to place a support beam in the ceiling of the first floor to support the floor joists on the second floor. The span is 17 feet but beam needs to bear on walls, so it will probably be a 18 foot long beam. (Heres where my problem lies) I want to build this new subfloor on top of existing ceiling joists and want to use 2x12 joists. I would like to have the new joists sit on top of beam and use sleepers on the outside wall to make up the difference. (To sum things up) I need my beam to be strong enouph to support the second story, but need to keep its height hopefully smaller than 12". I know there is the possibility of using steel, but would really like to use wood (lvl) I know you can sometimes use plywood or even steel to sandwhich between these beams for strucural strength. The second story will have bedrooms and one bathroom that is not directly over the beam. Could a structural engineer tell me what I could use that would be strong enouph but not be that high in height. Is there a way to do this keeping the beam height 6 or 8 inches ? I sure do appreciate any help a structural engineer would offer me on this problem, it has been a very frustrating one to deal with so far. Thanks, Tony............

 

[RockEngineer]

TonyV11
As you know there is more to this project than sizing the beam. In order to size the beam you need to know the tributary area. If the beam is in the center of the room and joists perpendicular to the room, your tributary area is then 1/2 the total width of the room. The 97 UBC requires all residential rooms including bedrooms to be designed for 40 psf live load. IRC allows 30 psf for sleeping rooms and attics but I would stick with 40 psf live load. You also have between 10 and 15 psf dead load (weight of the joists, subfloor, etc. Total load 50 psf (good round number). You won't find a wood beam 6" tall to span 18 ft and carry any significant load. You may be able to do it with 11-1/4 or 11-7/8 LVL. From the Willanette Industries web site

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

I pulled the load chart for their LVL Structlam 2.0E. A 1-3/4 x 11-7/8 with 18 ft simple span is good for 135 lb/ft. So you would need one 11-7/8 LVL or each 5 ft of room width. (135/50=2.7 use 2.5 and this is for half the load of the room). So if your room is 15 ft wide use three 11-7/8 LVL bolted or nailed together per manufacturer's specification. This is the easy part.

Now make sure you transfer the load all the way to the foundation without overstressing any of you existing structure.

You mentioned you are adding a 2nd story. Are your exterior walls adequate for this? Most older homes had 2x4 walls and won't take the extra load. Is your foundation adequate for 2 stories?

Now that I've given you enough information to get you into trouble I will tell you that getting the help of a local structural engineer to take a look at the whole project is well worth the money. A dollar spent in the planning stages is worth $100 trying to fix the mess after the fact.

Good Luck

 

[boo1]

Well said!