Another clear span question

[mart]

As spring is unfolding here in Alaska, I am making plans to set some posts for a sawmill shed. I am looking for some advise on how big a timber I should mill for the front. It will be open fronted, flat roofed, 10, maybe 12 feet high in front and 8 feet in the back and 12 feet wide. It will be closed in on three sides. I haven't determined how wide to make the clear span yet. I'd like to go as wide as possible. The current sawmill, an LT 30, needs at least 20 feet but I'd like to go 28 or 30 feet for the opening. I plan to use full thickness 2x12s for the rafters and either a clear vinyl roof or metal. The back will not be clear span and will have a post every eight feet.

I used this calculator and came up with a 6x16 passing the deflection tests for a 30 foot span. It looks like I'd need to go 8x16 to clear span 32 feet if I opted to go that far. This is with a 4000 pound permanent load. Am I reading it correctly?

Design for Bending

I'm also not opposed to welding up something like this that I found in the clear span trusses thread. It would of course not be pitched but straight for the front of the shed in place of the beam. Your thoughts are appreciated. Thanks.

[Don P]

At 12 feet deep plus 1' of overhang so call it 14', half the roof is bearing on the back wall, half on the front, so 7' x 32' opening= 224 square feet bearing on the beam. 4000/224=18 pounds per square foot. I use 25 snow+ 10-15 psf dead load here in the VA mountains. I think you are underestimating the load. I believe Anchorage uses 50 psf but you need to get good local numbers.

You would possibly be better looking at a gabled truss spanning the opening.  Is the building overall going to be longer than 32'?

[mart]

Thanks. I've done a fair amount of conventional building but never delved into the clear span aspect of construction. Trying to decipher some of the calculators is taxing on my rather limited mental capabilities.

The shortest the building would be is 32 feet overall. I prefer two foot overhangs so the roof would be 16x32 at the smallest and 28 feet between the uprights in front. I'm not opposed to creating a glulam beam or using a DIY welded beam like in the picture. I certainly prefer to overbuild when it comes to the clear span.

As far as the gabled truss, I may have to consider that. I hadn't really thought much about them. That may work better for me.