Rafter Strength?

• 06-30-2007, 09:18
Curt
Rafter Strength?
Anybody know how strong rafters are? I'd like to hang a hammock in my garage but I'd rather not pull my house down on top of me :)

Seems like it shouldn't be a problem, but I know the forces get magnified depending on the angle and these things are made to support weight from the top, not necessarily from the bottom.

Any construction/engineer/architect advice is much appreciated!

-Curt
• 06-30-2007, 13:40
slowhike
some of the others (engineer types) will chime in soon , but just a thought that comes to mind... if you suspended a pole (2x4 or top rail from a chain link fence) from the rafters, it would give you lower points to attach the hammock on each end of the pole if that would help.
it could be attached parallel with or across the rafters & be attached at multiple points on the rafter(s), so i would think it would be plenty strong. of course you might get some unusual end to end swinging unless you did something to remedy that:p
• 06-30-2007, 22:12
Just Jeff
Lots of variables affect the answer...and I'm not an engineer or home builder, but here's my amateur opinion. :D

The reason a hammock force is so high is b/c of a trig function...the combination of vertical and horizontal forces based on the angle of the hammock supports. If you're hanging from two ends of the same rafter, the horizontal force acts as compression to the rafter. Assuming you're not bowing the rafter with the compression force, you're not going to compress a rafter to failure with hammock forces. So, if your rafter is one solid length all the way across (rather than two lengths of wood stuck together with a joiner), the only force you're really concerned with is the vertical forces. Depending on how it's constructed, your rafter may be able to handle that load. In theory.

But for stuff like this, do a risk analysis. Is the success worth the cost of possible failure? If this works, you get a new place to hang. If it fails, you could pull your roof down on top of you. Some rafters can handle it - there are even pics on the internet of folks hammocking from the rafters in AT shelters - but some rafters can't handle it. Look at your rafters...it's your call.
• 06-30-2007, 23:07
blackbishop351
I definitely agree with Jeff's assessment. I also used to be a contractor, and I'm not sure I'd trust a preexisting roof structure to handle a hang, at least not without beefing it up a bit. Most stick-built roof systems are designed without a huge amount of stress leeway above their normal operational load. Engineered roof trusses might take it, but I'd be leery. I think the best bet would be to hang from a good solid floor/ceiling joist, like one would find in a garage with a living space upstairs, but I'm still not sure I'd try it myself.
• 07-01-2007, 00:46
warbonnetguy
the house i live in is 50 years old and looks like it was built by a diy on a budget. as a result the celing studs in my garage are only 2x4's spaced 3 feet apart and i hang directly from them via eye bolts i hang diagonal across the garage, so each support rope goes to a different celing joist. the eye bolts are however near the ends of the studs (where they rest on top of the wall i'm assuming) they're probably stronger here than in the middle of the span. the one farthest out from the wall is about 3 feet out. crawl up there and look around. bounce on some of the studs a little and see if they creak and moan and give alot, or if they feel solid under some weight, just be careful. i definately wouldn't be suprised if they were strong enough.
• 07-02-2007, 10:10
Redtail
If one followed Slowhike's suggestion wouldn't the only force on the rafters be a downward one of your weight plus the hammock? That way you could choose something stronger to hang from the rafters to handle the greater stresses, in addition to the benefits Slowhike noted of the lower attachment points and more options in which direction you hang the hammock.