Building a pergola

[Melt In The Sun]

Hi all, this winter/spring project is now in the serious planning stages, and it's gonna be a big shade pergola for our west-facing backyard. I've attached a sketch of the general idea...I screwed up the measurements at the bottom left of the pool so still need to sort that out. The gray dotted lines are the HOA mandated setbacks, which are ignored all over the neighborhood so I will ask what the real rules are.

Has anyone ever built one? If so, how did you handle the sizing of posts/beams to make sure it doesn't sag? We will have some fairly long spans. I have a steelworker friend at church who can help with those longer spans if the dimensions required for wood start getting ridiculous...and I think they might. The one at the bottom of the picture that partially crosses the pool is about 16'. I would like to make that straight across the edge of the pool, but that may not be allowed, and would be 20'. The blue posts are a first-pass shot at where the 6x6 posts would be (ignore the ones outside the fence...just extra shapes).

Anyway, still mulling over things. We are trying to get as much shade as possible here, since right now the backyard isn't real comfortable in the summer afternoons...it'll still be hot, but shade would help things greatly. We'll get a coolaroo-type pulldown shade for the west side as well.

Any thoughts are appreciated!

 

[jblizzle]

You need to SLAM that pool ... it is looking pretty murky

You are going to be looking at some pretty serious beam sizes for a 16' span. I started designing a covered patio for previous house, but never followed through. My brother (architect) was suggesting engineered beams and the span was around 14'.

 

[Melt In The Sun]

Hey, once I fix my measurements I'll put the pool in there, and make it nice and blue for you.

I kinda figured about the spans...that's why I was starting to think steel. From a brief bit of looking around the internet yesterday it was looking like 3 or 4 2x12's glued and screwed to make a 6x12 (or 8x12) would probably do it...just kill me now.

 

[jblizzle]

I would not suggest trying to make your own beams like that. Stick with steel or an engineered laminate beam.

There are some calculators out there to make estimates ... the beam size is also influenced by the length of the cantilever beyond the posts. The spreadsheet calculator that I found before appears to not work any more.

 

[woodyp]

Yeah, there is a span calculator online for different sized members. Had one, but lost it during the recent hard drive crash. You can always use galvanized commercial steel members for the long spans and top those with 2x6 or such. You'd be quite surprised how long a span a laminated beam will run.

 

[Melt In The Sun]

All the span calculators I've seen are for floor/ceiling joists, so they are assuming a regular joist spacing and some kind of load...so they're not really useful here, since I just have one beam. We'll see what the steel guy says!

 

[duraleigh]

A ceiling joist calculator will get you very close.

3 or 4 2x12's

I know from experience that three will pass the ceiling calculator.....maybe even two.

I have made beams (more than once) with a member on each side and 1/2 inch plywood or OSB sandwiched in between. Strong stuff and the assembly is a chip shot.

You have to solve some lateral flex issues but that member will make the span safely....almost sure.

Remember jblizzle this is not rocket science but redneck eyeballing with the help of some calcs.

You may not be able to get Southern Yellow Pine out there, MITS. That West Coast Spruce y'all use is made from cotton candy, recycled Styrofoam and silly putty that got a little too stiff to put in the egg.

Steel is discouraging to me in many ways....mostly aesthetics but if this is a DIY, it will take more than you and Sammy to walk that steel up a ladder.

Holy Benoli, I'm startin' to sound like those intractable service techs that come on here and blow us off.

 

[Melt In The Sun]

Thanks Dave, not sure what species we can get out here, since I've never paid much attention before. I know I can easily get redwood and douglas fir, but not sure what species the cheap stuff is. The ceiling joist calculator says a single redwood 2x10 would do it even at L/720 (about 1/4" deflection)...but I'm skeptical, and worried about long-term sagging. I would at least do two, one attached to (or notched into) each side of the post. Yeah the engineering says it's OK, but the redneck eyeballing is not so sure

The steel won't be DIY if that's how we go. I'm aware of the aesthetic issue...especially if it starts to look toothpick-y...but the steel guy has built more than a few of these so we'll see what he thinks. I can always skin a steel beam with wood, both to make it thicker and hide the metal. That seems like the safest bet, but, there's still a lot up in the air.

I'm picturing steel posts and beams (along the long dimension), skinned with wood if necessary, and a wooden structure from there up. That would make the bones of the pergola virtually indestructible, and I can handle the rest myself without any trouble...maybe not even needing Sam's help!

 

[jblizzle]

It is not just the sagging of the beam, it is the warping. In previous neighborhood, one of the builders went cheap on the covered patio beams using a one or a pair of 2x6 I think ... within just a couple years they were all warping and twisting and looked horrible.

Friend of mine built a large covered patio which he use metal posts (he welded them with a mounting plate on the bottom and a U on the top to hold beams) which he got powder coated. Then he used nice big rough sawn beams across a pretty good span. That is carrying more weight than you will need to, but I could get some pix of the setup if you like. Looks really nice with the rough sawn beams that he ordered from one of the local lumber yards.

 

[JohnT]

What are you planning on putting on top?

 

[Melt In The Sun]

Not entirely sure yet. The basic pergola would just be beams, then a layer of 2x6 or 2x8 rafters every 24" or so (would have to work out the spans for this too), then a layer of 2x2s for shade. Similar to the picture here...no curved front, but the same basic structure:
http://archadeckwestcounty.files.wordpr ... d-area.jpg
That would be fairly simple and inexpensive to do.

Bekah has fallen in love with this idea, but we aren't millionaires...that's not the kind of thing you can buy off the shelf.
http://s39.photobucket.com/user/sugarfa ... 4.jpg.html

 

[Melt In The Sun]

Jason, a picture of your friend's setup would be great.

 

[jblizzle]

That last one is pretty cool ... I assume there are pre-made panels like that available somewhere?

I will try to swing over there and gets some pictures (he is not too close to me so to/from work would be easiest, but have to make sure there is sun light)

 

[Melt In The Sun]

I assume there are pre-made panels like that available somewhere?

I'm not sure that assumption is correct....I sent the photo on to the steel guy though, he'll know.

 

[JohnT]

Not entirely sure yet. The basic pergola would just be beams, then a layer of 2x6 or 2x8 rafters every 24" or so (would have to work out the spans for this too), then a layer of 2x2s for shade. Similar to the picture here...no curved front, but the same basic structure:
http://archadeckwestcounty.files.wordpr ... d-area.jpg
That would be fairly simple and inexpensive to do.

Bekah has fallen in love with this idea, but we aren't millionaires...that's not the kind of thing you can buy off the shelf.
http://s39.photobucket.com/user/sugarfa ... 4.jpg.html

That second one wouldn't really be hard to do with a computer controlled plasma cutter. Setup might be a bear though.

How is the sun angle when you'd be out there? We built one out of 2X6s on edge, and it works really well because we mostly use the pool in the afternoon when the 2X6s block most of the sun from the deck. No closed-in feeling, but unless the sun is straight overhead it does quite a bit of shading. I had thought I might add shade cloth if the boards didn't do enough, but haven't needed it. But painting the boards is a PITA and I'm have trouble with warping on a few of them.

I saw an adjustable aluminum louver system that looks really sweet. Not sure of the cost yet, but I'm considering it for an upgrade. Pictures of one sysem here http://adjustablepatiocovers.com/arcadia.html One cool thing you can do is build a gabled roof to allow you to use trusses.

 

[Melt In The Sun]

Yeah, with enough money I'm sure I can get someone to make panels like that, but it's probably far out of our price range (and way over-improving for the house/neighborhood). I'm guessing at least several hundred $ per 4x8 sheet...at least.

The sun in the summer sets pretty much directly perpendicular to the back of the house. Using vertical boards parallel to the house is an option we're considering...but like you said, it provides total shade in the afternoon but not midday. Lots to consider.

The adjustable aluminum ones are really cool, but from what I remember they start at about 10k for a pretty small one.

 

[Melt In The Sun]

Well, some more messing around this evening. Jason, notice my pool now has nice blue water in it...no comments on how you can't see through the surface! And no, it won't actually be painted eyeball-searing blue when I'm done...

I really would like to put the top left post straight across the pool, but that puts me only 7' from the back property line and 10' is required...so unfortunately that's a no-go. That would have been really cool. The lines on the side are 5' from the property line for posts and ~38" for overhangs (that's how far everyone's eaves stick out).

I put some rafters on it to get a really rough idea of how it would look with a top on it. The beams are 2x10s to scale, and the rafters are 2x6. Bekah liked a picture she saw of a structure with two elevations, so I slapped that in there. Some problems right away though...the rafters are spanning nearly 14' at the widest part, which is way too far for a single 2x6, or even a 2x8. I want to avoid more posts, but that may not be possible...I just can't see where I would even put more posts in, given how the deck and bar are already laid out. Still haven't heard anything from the steel man...but that's looking more and more like the answer.

I am not at all a fan of the slight angle on the bottom right of the plan view. I could move that post around the corner to keep the right side straight, but then we don't have symmetry around the opening to the porch.

Anyway, still a lot of brainstorming. I will say being able to build this and look at it in 3-D is really nice....there's a view looking out from the porch at the bottom

[attachment=2:3awiyv97]perg2.jpg[/attachment:3awiyv97]
[attachment=1:3awiyv97]perg3.jpg[/attachment:3awiyv97]
[attachment=0:3awiyv97]perg4.jpg[/attachment:3awiyv97]

 

[jblizzle]

You may be able to get a setback variance from the county which would allow you to put the post straight out. It is something I looked into when I was going to build a covered patio.

What software are you using?

 

[Melt In The Sun]

Thanks...that's certainly worth looking into.

It's a mining software package that I use at work for geologic modeling + resource estimation (called MineSight). It has all the basic CAD functions, and I was already familiar with it, so there ya go. I bet you could do all the same stuff with Google Sketchup.

 

[duraleigh]

the rafters are spanning nearly 14' at the widest part, which is way too far for a single 2x6, or even a 2x8

Are you using a span calculator? I just spanned 14' 10" using 2x8's. My ceiling calculator was fine with it.

I can walk on the floor upstairs and it is quite acceptable. It has a bit more spring than some of the other spans but you would only notice it if that's your focus.

Of course, it is stiffened by the 7/16 OSB decking on top of the joists but you have a no load situation and a little flex is irrelevant.

Blocking in between the joists will help prevent twisting.

http://www.awc.org/calculators/span/cal ... cstyle.asp