Any builders/contractors that can answer a fairly simple question

[Patirck]

I have a big patio in the very back of my back yard. It is 25' x 18'. When we bought this house 12 years ago there was a leaning tower of rotten wood on it (Pergola kind of thing). As I recall, they were mostly 6"x6" posts for the vertical pieces. I would guess it was built sometime during the Eisenhower administration. There are holes built into the slab for these posts - one on each corner and two more evenly spaced along the 25" sides. There are no cutouts anywhere on the 18' span. I would like to cover the patio with some kind of wood structure and put the corrugated fiberglass stuff on top to keep the sun and rain off the patio. One of the main reasons I like this material is that it is light (the other is that it is cheap!). I'm in Los Angeles so I don't have any real weather to worry about - just sun and the few times a year rain storms.

I would like to put some outdoor furniture there and my keezer (and perhaps a TV). I have electrical to the patio now so wiring some lights and outlets would be no big deal.

My question is - how do I cover the 18' span without some kind of vertical support?

I would rather not have the space cluttered up with more vertical posts in the middle of it. I asked at a few local lumber yards and they looked at me funny when I asked for 18' 2x6. My original plan was to get some kind of simpson lawrence anchor and use 4x4 or 4x6 for the 8 vertical posts and tie them to each other with 4x4 and a t-strap. I would then put 2x6 on edge from one side 18' over to the other side. On top of these 2x6 I would put the fiberglass roof.

 

[joeybeer]

My guess is steel ... 3x3 angle iron ? I've never seen a span like that of any kind of wood - 5 yrs general construction exp

 

[broadbill]

What about an engineered laminated wood beam (Versi-lam I think they call it).

If that doesn't work, why not attach a wood footer to the slab and build supports off that?

 

[zac]

I have a license in Va, so I cant help yuh!!!! Get in touch with a contractor in Ca, and pose the question to him. Even with only holding up as little weight as you want to, 18' is a long open span for wood.

Would a simple wood truss system fit the bill? I know the local lumber yard stocks truses to 32' wide.

 

[tbel]

Either a glue laminated beam or floor truss would do the job. Neither will be cheap.
Any attempt at creating your own beam would likely end unpleasantly.<O</O
Glue Lam. would look the best but if your going with corrugated fiberglass I guess we're more worried about cost than appearance.

 

[tbel]

You could go with a roof truss that has a very low pitch. Scissor trusses might not look to bad.

 

[tbel]

Here is a Span calculator if you insist on using conventional lumber. It can be done.

 

[Patirck]

I am more concerned about cost - I was hoping to put something up for cheap - I loved the idea of just buying some lumber and bolting it together...

I guess I could check out the roof truss idea but I think that is going to be much more expensive than I was planning. For a 25 foot length, how many would I need? I am guessing they should be every 8 feet or so but it seems that 4 across the whole thing would be better - right on top of the vertical posts.

 

[martinworswick]

you could make a flitch beam- quarterish inch steel sandwiched between timber but to be honest straight steel would be strongest and cheapest,price up an rsj (looks like an I when looking at the end of it),thats the way i'd go if i wanted cheap

edit- or throw up another post mid span,one post won't be too intrusive.

 

[Patirck]

you could make a flitch beam- quarterish inch steel sandwiched between timber but to be honest straight steel would be strongest and cheapest,price up an rsj (looks like an I when looking at the end of it),thats the way i'd go if i wanted cheap

edit- or throw up another post mid span,one post won't be too intrusive.

Would I need a post every 8 feet along the 25 foot length or would a single post in the middle of the rectangle do the job?

 

[GilaMinumBeer]

A 2x12 Spruce-Fir-Pine Floor joist (Structural/No 1 / No 2 grade) will span that. I would double or triple it up tho'.

Use that span calulator linked above. Wet location = Yes (outdoor humidity is not controlled and affects the beam), Incised (means scored or cut) = No.

A typical live load for a Greenhouse is 10psf for your use I would suggest 30 to 40psf minimum.

 

[wildwest450]

A 2x12 Spruce-Fir-Pine Floor joist (Structural/No 1 / No 2 grade) will span that. I would double or triple it up tho'.

Use that span calulator linked above. Wet location = Yes (outdoor humidity is not controlled and affects the beam), Incised (means scored or cut) = No.

A typical live load for a Greenhouse is 10psf for your use I would suggest 30 to 40psf minimum.

+1, can you get southern yellow pine lumber(even stronger than fir)? A 2x12 will span that with no problem. Especially if you have no concerns of a snow load.



_

 

[Bobby_M]

I'd be looking at putting in a sun sail instead. It's about a grand but the cost would probably be a wash given how much lumber you're talking about.

http://www.backyardcity.com/Shade/3L-Rectangle-Sunbrella-Standard-Shade-Sails.htm

 

[tbel]

I like Bobby's Sun Sail idea, but looking just breifly at the website it says the Fabric is NOT water proof. I would assume with the pitch they put on it, it shed most of the rain any way but you may want to look into that.

With that corrugated fiberglass I doubt your spacing can be more than 2' on center.
If you were to go with the 2x12s as Gila suggests it would be easy to attach the pannels. I would elevate one side at least 18" higher than the other that would give you a 1/12 pitch and should easily be enough to shed the rain.

If you start looking at steel I'm not sure how you would fasten the pannels. I don't think it would be as easy as with wood.

 

[Bobby_M]

The challenge with the sails is really having beefy posts. There's a ton of lateral force on them due to how tight you need to make the sail. This size of a roof structure isn't all that trivial though given 18 x 25. Maybe splitting the 25' length down the middle is more practical. A 12' span is easier to deal with. You can avoid a middle post by using an 18 foot long I-beam or just put the center post in to reduce the cost of that beam.

 

[Patirck]

I'd be looking at putting in a sun sail instead. It's about a grand but the cost would probably be a wash given how much lumber you're talking about.

http://www.backyardcity.com/Shade/3L-Rectangle-Sunbrella-Standard-Shade-Sails.htm

That's pretty neat - I've seen those in a few places - mostly commercial settings. I was hoping for something a bit more water proof.

 

[brewmonk]

I am more concerned about cost - I was hoping to put something up for cheap -

That depends on how much you want your funeral to cost.

-

Hire a professional. Hell, hire ANY kind of professional.

Even if her name really isn't Candi, you are gonna be better off with ANY kind of professional help if you don't stop to consider how much an 18ft chunk of EFFin *TREE* weighs.

you need a structural engineer that has a triangle fettish.

good luck, stay safe.

 

[GilaMinumBeer]

you need a structural engineer that has a triangle fettish.

Depending on jurisdictional requirements, maybe, or at the least an Architect.

I dunno of any jurisdictions other than super rural that would not require at least a permit. And here, so long as you are using dimensional lumber, no architect or engineer required provided you have chosen a size that has published span and load data. Span and load tables are easily obtained. Usually free direct from the mill.

 

[Patirck]

This sounds like more than me and a friend can handle - I was thinking of bolting together some lumber using simpson lawrence stuff at home depot/lowes. I guess it will have to wait for a while...

 

[GilaMinumBeer]

This sounds like more than me and a friend can handle - I was thinking of bolting together some lumber using simpson lawrence stuff at home depot/lowes. I guess it will have to wait for a while...

Just realized you are in CA. So, umm, yeah. Doubt you'll be allowed to do anything without a permit and doubt you'll be able to do anything simple and easy assuming they enforced strict siesmic bracing.

Nothing is easy in CA from what I hear. There are too many laws against easy there. And Simpson Striong Tie / Lawrence is known to cause cancer in the state of...

 

[prrriiide]

Just realized you are in CA. So, umm, yeah. Doubt you'll be allowed to do anything without a permit and doubt you'll be able to do anything simple and easy assuming they enforced strict siesmic bracing.

Nothing is easy in CA from what I hear. There are too many laws against easy there. And Simpson Striong Tie / Lawrence is known to cause cancer in the state of...

I think the Simpson stuff is earthquake-rated provided you use the right items in the right places with the right nails.

FWIW, when I framed houses (way) back in college, we used 2x12 southern yellow pine for garage joists. They'll span 18'.

One way you could possibly get it done is to do a gently-sloped (4-in-12 or less) hip roof structure.

This site gives a pretty good overview. Of course, instead of walls, you would have some pretty serious beams running around the perimeter of your structure. But that's true with a flat roof or a hip roof.

 

[GilaMinumBeer]

I think the Simpson stuff is earthquake-rated provided you use the right items in the right places with the right nails.

They are, but most jurisdictions permit departments don't employ staff engineers to ensure the proper parts are specified in the proper places and Inspectors generally just require the manufacturers recommended fasteners in every hole of the tie.

So, as to the parts and peices needed, a permit department "may" require an Engineers Certification of the design to ensure the minimum siesmic standards are met.

 

[prrriiide]

They are, but most jurisdictions permit departments don't employ staff engineers to ensure the proper parts are specified in the proper places and Inspectors generally just require the manufacturers recommended fasteners in every hole of the tie.

So, as to the parts and peices needed, a permit department "may" require an Engineers Certification of the design to ensure the minimum siesmic standards are met.

Man, those people would **** bricks if they saw some of the...creative...engineering up in the hollers around here!

 

[GilaMinumBeer]

Man, those people would **** bricks if they saw some of the...creative...engineering up in the hollers around here!

Actually no. After a few years it's just not even funny anymore.

The average joe is more likely to come up with creative compliance than the licensed engineer. The average joe is most concerned with long term stability and tends to over-"engineer" (If a 2x12 is good then a 2x16 must...) wheras the "design professional" is more concern with the name assosiated with the astethics (Sure, it can withstand a 9.0 Richter earthquake but it just doesn't scream "look at me").

It's annoying.

And furthermore, the average joe conceeds he/she knows nothing of minimum code wheras the design professional has read just enough to think he/she can argue their way out of an astethics deal breaker.