Pergola joist/beam sizing help

CarpenterRN · Apr 19, 2011

Hello. I was wondering if the experts here might be able to help me with some sizing since I have only done one pergola. The local lumber yard is more familiar with structural aspects of homes and decks rather than pergolas. I know with less load you can use smaller members, but the span chart I have only shows ratings for cedar as deck joists, which is the same one the lumber yard has.

Joists: unsupported span of 12'-5 1/2" with 2x2 cedar slats 5-1/2" o.c. No traffic of course on top of the joists. Would 2x8 western red cedar work at 16" o.c. or do I need to bump up to 2x10? Or reduce the o.c. spacing? My span chart shows 11'-4" for 2x8 WRC floor joists at 16" oc and 12'-6" for 12" oc, but nothing for ceilings.

Beam: 3-6x6 posts. Unsupported span between posts 1&2 is 8'-6" and between posts 2&3 is 8'-2 1/2" :whistling(HO installed them last year thinking he was going to do this himself.) Will a 2x10 WRC on each side of the 6x6's work or would I need to go up to 2x12?

Would Ledgerloks work well to attach the 2x beams to the posts or is there a better way?

And as far as just the aesthetics go, do you typically use a 2x beam one size larger than the joist size?

Thanks.

Warren · Apr 19, 2011

I think what you have called out works ok. This will not need to support any weight other than its own. For aesthetic reasons, as you surmised, I think it will look better if the beam is larger. In lieu of the ledger locks, could you notch the posts to accept the beams?

CarpenterRN · Apr 19, 2011

Thanks Warren. Notching the posts? That would have to be up to the HO. He gave me a picture of a pergola and said, "This is what I want." In the pic, they were just attached to the outside of the posts. I mentioned Ledgerloks since I thought they might be less conspicuous than lags or through bolts, but would still be structural.

John Hyatt · Apr 19, 2011

I am really big on landing beams on posts,old school that I am, any bolt conection is going to provide movement down the road and sometimes a place for rot to start.

If using pt lumber I flush out the joint, make the conection with a simpson steel plate and wrap the post and the beam. Over here we have a Redwood broker that opened up a retail outlet so 6x6 RW beams can be had using them I make the conections with ss screws with a rosett cover plate. Those beams are around $15 a RF but they save a lot of time and look really good.
John Hyatt www.deckmastersllc.com

ScipioAfricanus · Apr 20, 2011

I have never really checked on it but I don't believe there are any specifications in the IRC or IBC for Pergola rafters and such.

It is mostly a matter of local jurisdictions saying what is required if anything since a Pergola is strictly speaking a decorative item.

They still don't want it to fall over of course but it is mostly a matter of aesthetics.

Andy.

CarpenterRN · Apr 20, 2011

Thanks for sharing your detail, John.

Yeah Andy, that's probably why the lumber yard doesn't know much about them. My concern with sizing would be more of ensuring there wasn't any sagging of the members over time than anything else. Thanks for the input.

redwood · Apr 20, 2011

I've probably done 500 pergolas, most of the time we sandwich the posts, and bolt them. Many have 1x or 2x trim under the beams.

Your dimensions are fine, in fact, you could use 2x8's for the beams as well, but for asthetic reasons, we try to have the beams a little larger.

Also for asthetic reasons, I prefer to use either 3x or 4x material.

ScipioAfricanus · Apr 20, 2011

This shows 2x10 as the mains, notched into the 6x6 posts and 2x8s as the rafters.

I think, as Mark may have said, 2x12s would look better. No doubt.

Andy.

CarpenterRN · Apr 22, 2011

Wow, that's a lot of pergolas Mark. Yeah, bigger lumber=more cost and I don't think the HO will want to put that much more into it. Besides, around here some of those sizes would be special order and you never know what you'll get sometimes, quality wise.

Nice sketch Andy. I would rather notch the posts since it's easier to set the beams alone.

Thanks for the advice you guys. I appreciate all the help.

greg24k · Apr 22, 2011

ScipioAfricanus said:
This shows 2x10 as the mains, notched into the 6x6 posts and 2x8s as the rafters.

I think, as Mark may have said, 2x12s would look better. No doubt.

Andy.

What you have there Andy it looks right...I think taking into consideration the height of that pergola, assuming it would be 8-10', 2x12 will look very "bulk" it will feel like the whole top is coming down right on top of you.

Let's take 8' ceiling height as an example, and if you throw up there 5 1/2" coffered ceiling or even just 5 1/4" crown, you will get that claustrophobicfeeling if you know what I mean... This why I think the lumber sizes you used in your picture, will make a much better feeling when being under it and appearance as well.

Pergola joist/beam sizing help

CarpenterRN

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redwood

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