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I'm planning to build a relatively large wooden pergola of about 4 meters or 13 feet wide per 7.5 meters or 25 feet long.

I'm not planning to add a roof or extra crazy load to it.

On one end I'd like to attach the pergola to the wall of the house, on the other end wooden posts.

enter image description here Because I would be using 4 meter / 13 feet long rafters, do I need some intermediate support between the wall and the beams? What would be the recommended dimensions for the rafters section? I would prefer not to angle them.

How many posts should I use and with which section? What would be a safe beam(s) size?

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You could probably get away with two 4x4 posts on this, since the house would pick up a good amount of the load. I would run 2x6 trusses and cleat them to your house (someone will eventually want to hang something off it, even if that something isn't crazy heavy, so don't toenail this end).

I would laminate a 2x6 beam to go between your 4x4s. The problem you face here is that 25ft is too long for a single board to really span well. Ideally, I would want this beam to sit on top of the 4x4s, since it will be heavy as well. To make a laminate beam, buy the longest 2x6s you can carry (12ft sections should ensure you're not needing to do a lot of bolting). You'll want some lag bolts and construction adhesive that can work with pressure treat (even if you use cedar, the PT stuff is coated for outdoor use). Stagger the boards to make one 25ft length, gluing and bolting as you go along. You can then put the beam on top of the 4x4s and use screw plates to attach. You can then toenail the truss boards (with deck screws) to the top of the beam

  • This is a really helpful answer! Suppose I could get 25ft 2x6 beans, could I get away with using two of them to sandwich two 4x4 posts? – Juan Cortines May 8 at 13:18
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    Probably. Just be sure to lag bolt both ends (or add two galvanized bolts and drill holes first) – Machavity May 8 at 13:20
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    like this? => dhcsupplies.com/store/p/… – Juan Cortines May 8 at 13:27
  • Yep, that would do it – Machavity May 8 at 13:29
  • I found a local sawmill which can do 25ft so I have a last question: What would be the minimum space between rafts/trusses, so the two 2x6x25 are not overloaded? – Juan Cortines May 8 at 20:00

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