spudley, I wanted functional dormers and I hate the small 2' wide dormers with just the width of a window. That is why I am stick building the roof instead of just buying attic trusses. I am paying alot more, but getting a very functional space. Downstairs is 26 x 30, so 780 sq. ft. Taking out the area for the stairs, I will have over 600 sq ft upstairs. Full 9' ceilings out to the front wall in the gable dormer, 6' height at the back wall under the shed dormer.
Attic trusses for a 26' span have a 12' wide opening, so 360 sq ft, then take out 40 sq ft for stair opening and it would only be 320 sq ft. And that is only at 7.5' height in the middle. Not usable as a studio apartment...
The most usable space would be to have shed dormers on front and back, but I do not like the look of shed dormers, so I just used it on the back. I was originally going to just have a 8-10' wide gable dormer on the front, but I wanted more space. I browsed dormers and thought about doing a nantucket dormer which is two gable dormers connected by a shed dormer between them. I wasn't sold on that look, so I finally decided on a gable dormer flanked by two shed dormers. The original drawings the engineer gave me had the gable dormer as just an overbuilt gable on top of a shed dormer, which was cheaper, but I wanted a functional dormer with the full ceiling height out to the front wall. This also increased the cost by doubling up the LVL ridge beam and adding the LVLs between the steel beam and the front wall. Sorry for the dissertation, but that's how I wound up with this design...
For the floor trusses, you could use I-joists, but you cannot run HVAC ducts through them, which I may do at some point, and it also is a pain in general for running plumbing and electrical because you have to drill holes in specific spots.
You could also avoid the steel beam with really tall floor joists, but I wanted to reduce wasted height, so with a span of only 13', the 14" tall trusses are plenty sufficient. The beam will also be useful for pulling engines with a chain hoist if I ever need to do that.
Here are the truss calculations. It is pretty straightforward. Live load limit is deflection of L/480 and total load deflection should be less than L/360. To get those deflections, I needed a beam with I >= 341 in^4. So I could have used the following beams: W12x45, W14x38, W16x31. I chose the 12" beam so it would not protrude so far down below the garage ceiling. I also stepped up to the W12x50 just to get some extra stiffness and less deflection.
http://pelicanpointroad.com/garage/W12 Calc.pdf
Beam dimensions:
http://www.engineeringtoolbox.com/american-wide-flange-steel-beams-d_1319.html
The LVL header that supports the beam is plenty strong enough. It has 2 jack studs under each end and is less than 4' wide. I could have used a column on that wall, but I am a symmetrical guy, so I wanted the 1st floor window centered on the side of the garage.
The LVL headers above the garage doors are supporting even more load than the one under the steel beam...
I am a mechanical engineer, perhaps that is why I am so detail oriented about the garage design/build. I am learning alot now and will continue to learn through this project!