Pergola Build Question

[Jim Roche]

Hello,
I'm building a pergola out of PT wood on my back patio and have a question about the cross members. The pergola is approx 19ft long and 13ft wide. I'm using 2x6's for the 13ft cross members and attaching them using joist hangers. My question is about wood movement, should I cut the cross members flush to length or should I cut them a tad short?

Thanks in advance for your advice.

Jim

 

[Mike Davis]

Wood moves across the grain, almost none in the length.
I always cut to fit the length.

 

[Jim Roche]

Wood moves across the grain, almost none in the length.
I always cut to fit the length.

Thanks Mike!

 

[Dee2]

My experience is that if you put PT down wet, it will sag some between joists and butt joints will open up. I hope YMMV.

 

[demondeacon]

When we built our pergola we drilled holes and connected the cross members to the posts with long through bolts. They look nicer and will be stronger than hangers. My two cents.

 

[Mike Davis]

While the stringers are still wet clamp them together, set the ends on blocks, stack heavy weight in the center.
Let then sag and dry.
When dry, unclamp turn them over and bolt into the headers with the arch high in the center.
Now that are less prone to sag because they are arched.

 

[demondeacon]

Sounds like you have already bought your lumber. If not, and you live near one of the 4 or 5 NC locations of Professional Builders Supply they carry "twice dried" outdoor lumber. It is much higher quality than the sopping wet stuff you might find at a big box store. They sell to non-contractor walkups.

 

[Jim Roche]

Sounds like you have already bought your lumber. If not, and you live near one of the 4 or 5 NC locations of Professional Builders Supply they carry "twice dried" outdoor lumber. It is much higher quality than the sopping wet stuff you might find at a big box store. They sell to non-contractor walkups.

Yeah, unfortunately I did already buy the wood but made a note of Professional Builders.


One more question for the group.. I'm going to double up the "ribs" on the outside 2x8's and the middle, these will connect to the upright 6x6's. Would you use glue and screws for these laminated beams?

Thanks!

Jim

 

[wndopdlr]

One more question for the group.. I'm going to double up the "ribs" on the outside 2x8's and the middle, these will connect to the upright 6x6's. Would you use glue and screws for these laminated beams?

I would use the screws and forego the glue. I would also thru bolt the 2X8's to the posts.

 

[John Jimenez]

Agree with Wally….don’t waste the glue but def screw the ply’s that make up the beam together. Def use carriage bolts to secure the beams to the notched post. Also, be sure to use the correct galvanized nails with the joist hangers and not screws. Send some pics when it’s done!

 

[Jim Roche]

Agree with Wally….don’t waste the glue but def screw the ply’s that make up the beam together. Def use carriage bolts to secure the beams to the notched post. Also, be sure to use the correct galvanized nails with the joist hangers and not screws. Send some pics when it’s done!

Why the galvanized nails and not screws?

 

[Mike Davis]

Screws break easily, they are not adequate for construction stresses.

 

[gamiller3rd]

It’s an issue of holding power (screws) versus shear strength (nails). As Mike says screws break or shear off easier than nails.

 

[John Jimenez]

I think the specs on the joist hangers (probably Simpson) tell you that you have to use a particular galvanized nail. Galvanized because the hangers are galvanized and nails because of the shear strength as others have pointed out. From personal experience….buy yourself a palm nailer….most those joist hangers require 10 to 12 nails per hanger….Palm nailer is a life saver!

 

[Ecr1]

Simson makes a code compliant screw for joist hangers. They are the SD connector screw. Most Box stores stock them.