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Old 10-03-2010, 10:51 PM   #1
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patio roof with 2 hanging swings - what size rafters?


Hello all:

I just finished the basics on my patio roof. It's roughly 10'x10', supported with treated 4 4x4s (bolted into cinderblocks and blocked/nailed with 2x4s at the bottom on 2 sides), and there are 2 pairs of 2x6's joists (cedar) supporting the whole roof portion. 6 2x4s (fir) as rafters (with 4 hurricane ties for each) and 6 2x2 purlins (fir) on top. I'll be adding Suntuff clear roofing on top of the whole thing.

The question: If I want to hang 1 (or even 2 equally distanced) 'skychairs'--(a swinging sling chairs that swing from one rope), would adding a 2nd 2x4 rafter to a overhead rafter be enough? The span of the 2x4s is roughly 6 feet (and i cut them myself from 2x6's, so they are actually 4 inches, not 3.5'' like regular factory 2x4's).

So I'd tie (with mountaineering webbing) the swing to the middle of the 2 2x4s. No eye bolts, just rope/webbing.

My instinct says it would be strong enough. 2 2x4s, fir, protected from rain, nailed together. Any thoughts? Hopefully the attached photo explains it enough. So, maybe 200 pounds weight for each swing--we're all under 200 pounds.Thank you...
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Old 10-04-2010, 08:48 AM   #2
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Posting a picture of the structure would help. I can't tell by a description how it's made.
Ron
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Old 10-04-2010, 09:40 AM   #3
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pictures of the patio


here some pix of the structure--again, the current 2x4 rafters span 6 feet , resting on 2x6 cedar joists sandwiching 4x4's :

patio1.JPG
patio2.JPG
patio3.JPG
patio4.JPG
patio5.JPG
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Old 10-04-2010, 10:33 AM   #4
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I would have used 2x6 roof rafters even without the swings. I don't understand the 2x4 floor joists either, but...
Are you throwing the rope over the rafters?
From the structure's framing, I take it you have no snow load?
You would need lateral bracing from the roof to the 4x4's.
The way it's currently built, I would not install any swings.
Ron
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Old 10-04-2010, 12:05 PM   #5
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Quote:
Originally Posted by Ron6519 View Post
I would have used 2x6 roof rafters even without the swings. I don't understand the 2x4 floor joists either, but...
Are you throwing the rope over the rafters?
From the structure's framing, I take it you have no snow load?
You would need lateral bracing from the roof to the 4x4's.
The way it's currently built, I would not install any swings.
Ron
a) very little snow here--once every 4 years or so, and lite
b) the floor joists are actually 2x6, so the picture doesn't show it correctly
c) i'm planning on adding 'elblow' supports in both directions at the top of each every 4x4
d) the webbing would be thrown over the middle of a rafter (or rafter pair, if I double the rafters), tied tight (with a constriction knot) in the middle of the rafter, so that the rope doesn't slide down. 2 12 pitch


I guess one question here is this: 2 2x4's laid vertically next to each other, nailed to each other, for a 6 foot span--how much bearing load can that handle?
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Old 10-04-2010, 01:27 PM   #6
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I don't think the 2x4's will handle a dynamic side to side force. The lateral bracing will need to be pretty substantial to handle the force as well.
Ron
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Old 10-04-2010, 03:12 PM   #7
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I agree with Ron. Your two 2x6's should be nailed together, not on each side of the post, otherwise they act as individual members, not a built-up beam. Cedar is the weakest wood for the application with a fb1050 (if stamped #2), and properly nailed together, they could carry a load of 840#. If Doug. Fir, total load of 1340#, a big increase.
your roof span, plus the tail overhang = 7 x 5 span to posts = 35 x 37 (30# live load, 7# dead load = 1295# Your cedar beam, IF nailed together would be weak by 50%. https://www.auroragov.org/stellent/g...ion/027548.pdf

Your rafters (24o.c.) should have a maximum span of 67: http://www.awc.org/calculators/span/calc/timbercalcstyle.asp?species=Douglas+Fir-Larch+(North)&size=2x4&grade=No.+2&member=Rafters+ (Roof+Live-Load)&deflectionlimit=L%2F360&spacing=24&wet=Yes&i ncised=No&liveload=20&snowload=-1&deadload=10&submit=Calculate+Maximum+Horizontal+ Span#answer

I suggest you run the deck and the roof by your local Building Department for minimum safety review. Here is the older Deck Code: http://www.lancova.com/deckinfo.pdf

Gary
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Old 10-05-2010, 12:10 AM   #8
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great answers, thank you!


yes, your answers rock. no swings, we'll just enjoy the view.
And I'll definitely consult the .pdf

By the way, what is FB1050?
-v

Last edited by diyman2010; 10-05-2010 at 12:13 AM.
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Old 10-05-2010, 12:30 PM   #9
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fb is fiber bending - the rating of different species of wood used in a project. Cedar is the weakest with most building departments not accepting it as structural due to it's very low strength rating. Scroll down a few pages and note the changing spans for the different woods used of the same size: http://books.google.com/books?id=HMu...tables&f=false

Gary
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