Pergola

[Tater Head]

I am planning on building a 16' by 20 ft pergola. The rafters will be 2 by 8 Douglas fir 16 ft. long. I am having trouble on deciding the size of the 20 ft. end beams that the rafters will rest on. This will be a clear span. Does any one have a suggestion.

Thanks in advance.

Larry

 

[Bass Man Bruce]

Re: Pergola

Your local building dept. should be able to give you your answer.
Not knowing where your from I have no clue as to any snow load concerns.

 

[Bigprairie1]

Re: Pergola

If you have a little more info on it it would help with some feedback.
What will the pergola be used for? Grape vines? Open top & decorative with some top/side lattice? Outside patio seating area?
The support beam does not need to be that big to support open/decorative rafters. If it was me I would go with either a 2x8 (mininimum) or a 2x10 (maximum-preferred) and double it up. I would screw the two support beams together every foot. More importantly, when doubled up aside from the strength advantage, its a lot more stable to mount rafters on at the end connections and it sits on the vertical (4x4) corner beams with almost a perfect width fit.
Anyways, if it is decorative only you might want to look at getting/using cedar for the rafters and stain them....much better looking.
If you get really lucky and find a nice 4x8 cedar beam that would make a great 20' for the support beam.
The trickier part whethers it fir, cedar or whatever is going to be to find a 20'er. This length might be a special order.
My two bits.
BP