It depends on how many posts holding up that beam.

The Porch Guy

Span 18' means 18' between post porchdude.

2 - RSC 2x12's will not span 18'.

Al

Thanks Al
The Porch Guy

So do I have any options to span 18'. Something like a cedar (or doug fir, or cypress) timberframe beam 6x10 for instance. I'd love to find out how to figure this out on my own if someone can offer a link to beam span tables for very low loads.

Thanks for your time.

What size/spacing are the cross beams that will sit on the beam?
14' long 2x8s 16" apart will put more stress on the beam than 8' long 2x2s spaced 24" o.c.

Mac

That is a pretty long span. Certainly it can be done with a gluelam or steel, but I don't think you will find any simple beam tables that go that far. If there is no load on the beam, I'm fairly sure that a douglas fir 6x12 would span that distance.

As built by Mac says, more info is needed to calculate the loads per lineal foot on the beam.

Mark

I have a pole house style timber frame house. The perimeter beams that carry the roof rafters are 6x14 and 6x16 for 16 foot centers for the poles. These are doug fir that was rated as #1. Also, these are full dimension - even after drying out they are pretty close to full dimension - around 13 3/4" or 15 3/4" deep. The only loads carried by these are the roof loads, which in my case includes snow or wind loads. The reason people put in extra intermediate posts is because the beam dimensions don't even come close to scaling linearly with the span you want. And the same is true of the cost.

For a lot of years garage door headers made up from two pine 2x12s spaned 20 ft with the joist system and the roof landing on it.Not to mention the garage door.

When I was framing new construstion we always included 1/2'' plywood inbetween and used construction adhesive. I framed up many a house doing it that way with O problems down the road or with the permit store. John

Thanks for the responses above. I'm hoping for another round of input if possible.

The design has changed a bit. The span we really need is 20' post to post. The purlin length will be 24' so 24" overhang on each side. The rafter legth will be 8' between beams with an overall length of 12' and again 24" overhang.
On top of the rafters will be another set of 24' long 2x4's.

So basically:

1----------------2
:
3----------------4

distance 1 - 2 = 20'
1 - 3 = 8'

I'm looking a spanning the 20' beam with an LVL beam and wrapping it in Ipe. The rafters will be 2x8 Ipe.

I'm thinking that a 1.75x11.25 LVL will span this length, but I'll certainly confirm.

The top load comes in at about 2000# with all the Ipe and beam weight, so I'm thinking the lineal load on each beam is (2000#/2)/(20') = 50#/ft. for the dead load.

I am concerned about deflection with respect to apperance, but there really shouldn't be any live loads.

Am I on the right track here? Is a steel beam a better solution? I could cut the weight in half with cedar I guess.

Bemis it might be a good idea to scurry on over to your local permit store for some insite. Or hire a Deck Pro to give you a total plan. J.

John,

Thanks for the lack of input. Feel free to restrain from sarcastic responses in the future.

cheers

No funning at all,the permit store is the first place you should go with a project like that. J.

I googled beam spans, and there seems to be several sites to calculate your issue. Hope this helps.

No permit is required for a free standing structure in my local. Either way the guys at the planning dept. aren't going to size a beam for me, nor would I want them to. I'll have a PE sign off on the final design. I would like to get close enough design wise to estimate a material list to price out.

With respect to beam sizing calcs online, they don't relate very well to a pergola. Most calculators and sizing charts start with a 10# dead load and a 40# live load and go up from there.

Either way, thanks for your input

JohnA person never knows who is working in the permit store, I have goten some really good advice from a city Worker over here I just have to time it right making for an in with him. Ya Never Know it all depends on who they hired, its worth a shot our taxes are paying for it,you got it coming and there is an outside chance for some good stuff. Same deal with a Deck Pro most likely a local guy will know about material,footings, ya know local stuff and would hire on as a consulant you needing a plan and all that.

If this project was mine to bid the Framing would be built from double 2 x12s landing on 6x6 posts,metal conectors,wraped in ipe. Total with in range if not over Kill for what you are placing on top.

And I am sarcastic, and a real Jerk, but I know what the flock I am talking bout. J.

I'm really late, so you've probably already done something...but here's my 2 cents. I attached a 12dx22w ft pergola to the back of my house. I wanted to minimize the number of vertical posts, so opted for a steel I-beam clad in wood for my longest span. I'm really happy with the open expanse instead of having 4 posts, and it is uber-stable.

I am dealing with the same issue (long span for pergola.)

I have a lot of experience with wood, but none with steel.

scvinyl, how much does a 22 ft steel I-beam cost? what size beam did you use for that span?

What I do on long pergolas that folks only want 2 post on is move the post in letting the beam cantilever on both ends. For example I did a 12x24 pergola, ledger attached to house 24' 6x12 cedar beam paralell to house. I cantilevered the beam 4' on each end that way the beam only was spanning 16', then used angle brackets from post to beam on each side of both post. Ran 2x8's on top of the beam w/usual 2x2's 4 inches on center. It's a lot easier to put up a 6x12 RSC beam than a steel beam plus the wrap that goes with it. Hope that helps.

Al

Al,

I'm thinking of doing something very similar to what you describe. I will be spanning 19', but large angle brackets will reduce the effective span.

The current plan is either a large WRC timber, or a wrapped LVL to span the length.

The material cost of wrapping a beam is significant.

What does a 24' 6x12 cost btw?

thanks

bemis, Wood cost vary greatly depending on your location, but it's not cheap anywhere.

Al

Fantastic work! Woowwww

Why cedar and not pressure treated wood? I'm asking because I'm going to build a pergola too.

Thanks.

Cedar costs a bit more, but it certainly ends up looking better. No sap, less movement/ twisting, and typically less checking (cracking). I'm not a fan of creating and breathing a lot of dust using pressure treated wood, and this project made a lot of sawdust.

Good luck on your project.

Thanks. How much more does a cedar cost say comparing the same dimensions?

I'll check my PTW tomorrow that I installed on my kid's playset.

Upcharge starts in the order of 40% and goes up from there. Call a proper lumber yard and have them quote it both ways. It was worth it for me.

Bemis,

I love the pergola! Question on the pciture you posted though - What are the corner braces attached to on the inside of the pergola between the 4x12's? I can't see from the picture.

Also, with the post being supported exclusively by footing and flush mount hardware, so you have any wobble in the structure?

Thanks,
Sean

Sean-

The posts rest on a 8" sonotube of concrete wrapped in bluestone. The lumber used was 6x6 post 6x12 beams, 4x8 cross beams and 2x4 top boards. The angle pieces were ripped to a 4x6 dimension. The 4x8 looked too bulky for the structure so I took a couple inches off. There is essentially no lateral movement in the structure. I was worried that there would be, but I can push a corner and get very minimal movement. I was going to try timberframe joinery, but lack of time dictated screws. The corner braces got 8" timber screws doubled on each end. It pulled tight, and I'm happy with the way it turned out. A 16" circular saw was key to the fabrication. Rent one if you're thinking of a pergola with 6" timber.

Thanks for the compliments. I'll monitor the board for a bit if anyone has questions.

Cheers

Bemis,

Thanks for the reply! I am tackling my pergola project this weekend and I had a couple of additional questions.

1. I see where the corner braces that run parallel with your 6x12s attach, but how do the corner braces attach to the pergola roof that run perpendicular? I can't see that in the picture.

2. What technique did you use for the notches?

3. How did you attach the slats? My plan was to use FastenMaster 6" HeadLok timber screws from the top of each slat down in to the joists.

Sean,

1. There is a 4x8 section that supports each corner support in the direction perpendicular to the main support beams. It is screwed between the 4x8 cross supports furthest to each end. It worked out pretty well.

2. Notching was done with a circular saw and a homemade rip fence (plywood sheet). I clamped about 15 boards at a time together and cross cut it to the desired depth with the circular saw. I cleaned it up with a router bit, but it could easily be done with a chisel.

3. 6" timberlock screws from the top. A 1/2" corded drill came in handy.

Have fun

Thanks Bemis! Due to rain on Sunday, I was not able to complete it, but as you can see from the picture below, your design really inspired mine. However, because of the pergola backing up to a property line, I reversed the end ornamentation on the backside rather than just leaving it at a 90. I will also do this with the slats. It should give an interesting profile to it.

I'll post completed pics up this weekend.

Thanks again!

{{!gwi}}

Just about done...

{{!gwi}}

Sean - Looks like a great project. Hope you are enjoying it. That's quite a hammock! I need one of those.

Hello all,

Nice work. My question is about the wood material. Is it dry or green material that you are all using? I'm planning my project and wondering if it's worth spending more for the dry wood. My local lumber yard is saying that it's not much different. What do you folks think. My concern is the shrinkage of green wood and perhaps that will vary from species to species. Any help would be great. Thank you.

I used mostly dry western red cedar. A few beams were wet, and they checked once they were hung. If you're talking about pressure treated pine, plan on a lot of twisting and movement if you put it up wet.

Stating what wood you'll be using would help with a recommendation.

Hello,
I have a similar challenge, except my pergola is 18' x 16' OC spacing between 4 6x6 posts (already set). For various reasons, I did not want additional posts, so I need to make it work. The 18' side faces due south, so I wish for the top rafters (2x6, approx 22' long, allowing for 2' overhang) to run E-W along the 18' length. I was thinking 3x12 WRC between the 18' spacing, one on each side of the post, and the same between the 16' spacing. Then 2x12 at the mid point of the 18' span, running front to back to support the 2x6 rafters mid way. Does this sound beefy enough? I would also use 6x6 angle braces from each post to between each beam pair, about 30-36" down and out from post, to reduce effective span along 18' side down to about 12'

Thanks

believe you will need blueprints and an engineers stamp to build this, why not get him involved from the beginning?

The original poster used 6x12x24' to span the 18' span, so I think I will do the same. However, instead of 8' on the other side, I have 16'. I *could* add two more posts to break this up, and have 3 6x12 beams span the 18' distance between each pair of posts:

1------2
: :
: :
3------4

1->2 distance = 18'
1->3 distance = 16'
In my case posts between 1&2 and 3&4 are out of the question due to sight lines from the house (big window).

I could add 2 posts shown by *, although I'd rather not, since the deck extends beyond on both sides:

1---#---2
: # :
* # *
: # :
3---#---4

So, I am thinking 6x12x24' between 1&2 and 3&4, then 4x8 (or 3x10) 18-20' length between 1&3 and 2&4, but also at the mid point of the two 6x12 beams (where the # are above). My concern is the weight of that mid span beam on the two 6x12s. But based on the two examples I've seen here, it looks like the 6x12s will do fine. I do like the idea of splitting the top rafter lengths in two, like Bemis' example, so I can use 12' 2x6s instead of 20' (or longer). However, that would require two mid span beams front to back resting on the 6x12s, like this:

1==#=#==2
# # # #
# # # #
# # # #
3==#=#==4

= are the 6x12x24' beams
# are the 4x8x20' beams
then 2x6x12' running from 1->2 across the top in two sections split in the middle, much like Bemis'

A 6X12X24 is going to weigh a ton. Will you use a crane to place it or what?

I am asking because am trying to work through a similar project 4 6x6 posts at A=19-6 OC and B=10-0 OC

#---------------------------#
------------------------------
------------------------------ B
------------------------------
#---------------------------#

-------------A---------------

The framing on top will be very light, probably just 2X6 or 2X8 at 24" or 16" centers. This all sits over a 14'X42' Azek deck which faces NE. There are two sets of French doors entering into the house between the posts. We want maximum sunlight in winter and plan to cover the whole structure with 90% shade cloth in the summers. Summers are pretty brutal and we have really never used the deck in the summers as a result plus we have to reduce heat getting into the house. Winters are very wet 55" average rain fall and occasional 4-6" snowfalls. I was thinking of using pairs of 24' 2X12's for the main beams with 45deg braces to reduce the effective span to about 16' Would that be too little wood? I was leaning to that because I can handle the 2X12's without a crane. There is another 14' deck below this one so getting a crane to reach across it to place 6X12's would be a challenge. Thanks for your ideas.

Hi,

I'm guessing the 6x12x24' will be about 300-400lbs depending on the moisture content. With scaffolding, I think two of us can manage to lift it up one end at a time, 200lbs each end, or use a chain lift to get it above the post. The deck is pavers, and flat all around, so lots of room to move. I should have done this in the fall when I had a 120ft boom lift for painting the house! Worst case is I borrow the lift again, although I have to reach from the neighbours driveway as it is too big to turn the boom in mine.
My conditions are similar to yours, so using multiple 2x12s tight together will just rot, and I don't think singles will do the span without sagging.

Let me know how it goes getting the beams hoisted up. I am very interested in how it goes. I was actually thinking of 2 2X12s with a space in between so they would not rot (cut a notch on each side of the post to hold the beams). But after reading this post I think 6X12's Kiln dried doug fir would be the better way to go.

I just happened back upon this post. A couple of tips from my project.

1. we rented a portable lift (Roustabout) for placing the beams. They were in the 400-600 pound range if I remember correctly. They went up very easily and were held in place until the could be secured. It was a valuable investment.

2. Rental of a 16" makita circular saw was a big help. Cross cutting a 6" stock in one pass made the job manageable.

The 6x12"s that I used have not sagged at all. I did a fair bit of load calc's before I ordered material. These are easily sufficient to span with a significant load on them. No deflection at all. I would be concerned about 4x8's spanning that length though. You could end up with some sagging (deflection). What material are you using? How much material is going on top of it? If you want I'll run the deflection calcs I have and get back to you.

bemis: Thanks for posting a follow-up. Your design looks great, and I'm planning to follow it quite closely as I like the proportions. Could you tell us the height of the 6x12s from the ground? How far down and in do the diagonal braces extend?

I'm still undecided on the finish to use. I have a 4 post gate arbour finished in a solid colour latex stain to match the house trim colours and it seems to be holding up well after 2 years. But I may go with natural cedar for the pergola. I really don't want to refinish for a long time. Can you tell us what finish you used and how it is holding up? We get a lot of rain in the winter, and full sun exposure, so most finishes take a beating.

I have some time to think more on this one, since I fell and broke 3 ribs on the weekend, so this will be on hold for a month or so...

As for hoisting the beams, I was thinking of place 3 flights of scaffolding between the beams, just inside the outer edges, then use a hoist to drag the beam up the side of the posts, and letting it swing over the top of posts. I can anchor the scafolding to the post bases for stability. Doing the post against the house may prove tricky with only 12" clearance from the gutters.

Bemis, some deflection calcs would help me a lot. i have a 20' beam span, two beams spaced 10' apart. Beams are a total of 24' long and all they need to hold up is 25 14' 4X8's and some shade cloth. I was thinking either 2-2X12's on each post or 1 6X12, see the sketch.

Here is a link that might be useful:

This is my proposed home elevation. The pergola like structures on the roof is spanning about 15 feet. I propose to use Wood PVC composite pergola material of 200x100mm cross section without any intermediate support in order not to affect the architectural beauty. Can someone suggest if a WPC material of this size can span 15ft without intermediate support.

Hi @bemis My son & I are building a less elaborate Pergola on the roof of a 2nd floor deck and it appears that we need to use a freestanding design that is similar to your photos. Can you provide more details around the post design with the sonotube?