We are thinking of adding on to our house, 24' deep, 28 to 30' wide. The lower level will be garage space, and it would be nice to not have post in between the parking spaces supporting a beam for the floor above. The beam would be spanning the 28 to 30' width, so I can use 12' floor joist for the 24' depth. The ceiling hight in the garage area will be 10 to 12' tall, so the hight of the I-beam wouldn't matter, as I can easily keep a 9' clear space below the beam. The floor above will be bedrooms and bathroom area, I do not remember the loads per square foot for calculations, been 20 years since I had to think about it.Any feedback welcome, just in the brainstorming stage right now, starting some sketches, to get materials estimated, and cost figured.


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I would design this with the beam in the 24' dimension. Most span tables will allow much more than 15' for 2" x 12" joists of almost any species commonly used for construction. A 24' beam can probably be a GluLam using standard joist hangers for the joists. 24' x 30' = 720 sq ft. live load of 40 psf = 28800 pounds. 1/2 is supported by beam in center = 14400 lb 14400/24 = 600 pounds/lineal foot. Look at the table here: http://www.aitc-glulam.org/pdf/Capacity/DF_27.PDF and you would need either a 5-1/8" x 18" or a 6-3/4" x 16-1/2" Doug fir/Larch GluLam.This is not a particularly large beam and I would increase the size to 6-6/4" x 18" or even 19-1/2" to give a substantial increase in floor stiffness at a very modest cost increase. P.S. when you have this designed consider adding a hard point in one bay of the garage suitable for a chain hoist or even a come-along to use as an engine hoist. I suggested this to my neighbor about 20 years ago, and he put one in. When his then 8 year old son entered his teen age years they must have rebuilt 3 or 4 engines together, always using the hard point to remove and replace them.
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JoinedJul 21, 2012Messages4,584LocationMid-MichiganTractorNH T-1520 HST, NH TC33DA HST, Case DX26 HST, .Terramite T5C, . NH L785


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Brainstorming? (insomnia) My home's main floor is on 18" deep 2x4 'W' trusses 24" OC and interior walls are net 27' apart above where they span. There is no beam, and there's a raceway for the HVAC plenum down the truss centers. Family room below is 18' x 27' with no posts or beams. ('residential height' ~ 7' 6" to suspended ceiling. (pics on request ..
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)The steel beam proposed I'd guess to be all 12" or more unless say two set spaced for 8' joists above or other combo. (It/they could be between vs under joists if you add a lintel(s) to the bottom(s). Door header need not be below them but needs considered depending on which wall gets doors and their sizes/clearances. Ceiling might be higher than the bottom of a beam under joists (assuming 12" & 12"). Do check with an engineer, familiar pal/dealer about options/possibilities for such trusses, beams, lintels, etc (16" OC surely spec'd) vs simple joists & beam and compare costs of all the bits each thing considered. Ease of pluming/wiring facilities above/thru trusses (BTDT) is nice. Much to consider. Door header might could be tripled joists if on the short wall vs welded up or something. Doors on the long wall? 'W' trusses are hung by the top chord, so a header under their tails would o'lap nearly their full depth/height. (my garage's ceiling and door header are trussed.)Your building inspector/dept might refer you to someone for advice to their 'er liking (sure to green tag first insp). There are means ... and I apologize if I added confusion to a process whose method has been pretty much decided. Oh, and my guess on the beam 'depth' was based on a 28' wide x 82' modular home setup. Going from 4" x 8" to 4" x 12" steel to span the four main 'rails' (~27') was approved to eliminate all posts. (Going from 4" to 6" wide beam would mean more of its own weight/load to carry, to install, and +$$). Garage, entry from narrow end, is 27' x 30' and adjacent family room is 27' x 30.5'. btw, For o'all ceiling height one 'cross-beam' in each ceiling (4" x 4" x 28' showing) is cosmetically wrapped but not obvious/unsightly. tog