I have a garage (concrete block walls) that has an attic space I'd like to use for storage. I will be laying 1/2" or 5"8 plywood on the floor. Also, the overhead garage door weight is bearing on the attic floor, when the door is in the up position. The floor joists are 2"x8"x24' @ 16" O.C. I added a 2"x8"x24' sister beam to every other joist. There are no lolly columns and I want to keep the space open without a column. The width of the garage is 25'. I want to cut into the block wall and have a girder span accross the joists, bearing on the cutout in the wall. I don't want the depth of the beam to be more than 12". I'm not sure what I should figure for live and dead loads. What size beam do I need to carry the load and what options do I have? Laminated beam, Steel, etc.? Chazman
If I understand this right, you have 2x8's spanning 25 feet and you want to use the space above for storage. Even with the sisters, I would not put much load up there . You will definately get a pretty good sag in the center.If I were approached for this job, my first phone call would be to an engineer. The couple hundred dollars will be well worth it.
There's a lot more involved here. Your local code enforcement officer (if he/she is good/nice) could look up the span and load charts at minimum. Light attic storage is usually 10-15 psf minimum. Plus as you stated you have hanging load of ceiling, garage doors, etc. You could run a beam the opposite direction down the middle supporting all joists... it could be freespanning say double LVL or steel flinch plate perhaps. But to size it you have to the math. I'd also suggest Advantech T&G flooring with Polyurethane based Construction adhesive. This will really help the floor act as a unit and decrease bounce.