Which roof structure should I use? And Why?

[rjwoelk]

I need to get my tractor and firewood processor and supplies under cover. So I built a timber frame model of it. I have 2 choices of Roof structure. The Posts are 8x8 . Sills 8x8
perlins, girts, rafters, are 4x6. The tie beam with a truss roof system are all 8x10. The rafter system 8x8 these can be up graded to 8x10 if needed. The top plate 8x10. The usall 4x6 knee braces as needed for racking. These are not in the pics. This will give me a place to operate out of as well as keep things out of sun and heat in summer and cold and snow in winter. I presently have a
This is a 17x 36, 5 bent structure the first 2 house the tractor/ power plant, saw chip storage and a bag storage area to the right.  The floor is 4x6 joist and will be planked with 2x material. All comments are welcome.
Then the processor, then the Office, storage. etc. Will have a front porch with a roof as well, with a thinkin bench.


  

  

  

  

  

 

[Dave Shepard]

I've always preferred common rafter to priciple rafter/ common purlin. At 17' you should be able to manage the rafter thrust easily with common rafter.

[rjwoelk]

Thanks David, with a 4x6 rafter whould you go 4ft on centre I know it would hold it, Then I was thinking just use 1x boards to sheet the roof, use a roof membrain   material and then tin. I do not plan on insulation on this project but if it ever was used for something else, want to leave that option open.

[rjwoelk]

Forgot something, colar tie? If so top 1/3 is were i understand it to be.  The rafters will be forked and pegged.

[Don P]

A collar tie, to prevent the roof from being pulled apart at the ridge in an uplift situation is in the upper third of roof height. A rafter tie to restrain the spreading force of the roof as gravity forces the rafter feet apart is located in the lower third of roof height.

To figure the dimensions of the rafters, you need to know the design snow load for the area, the species and grade of the timbers being used.

[rjwoelk]

Thanks Don, I was planning on using 4x6 collar ties, just trying to keep my cut list from having too many different sizes. The plate will be 8x10 . 8x8 was just a hair under requirements, so 8x10 will be good and the 4x6 should be good, if 2x6 x 15 holds up on a 2/12 for 30 years and still straight on 2 ft spacing. I may change it to 32 inch. more for taking out the spring on the roof boards. Could just by Truss rafters but that defeats the timber frame, and I have the logs.