Submitted by me-chewbacca t3_1271pl0 in DIY
outofmemory01 t1_jed3cqv wrote
It's your house...you can do as you please.
But this is wrong...dangerous, and foolish. No disrespect intended.
That roof structure was designed to do its name "ROOF STRUCTURE" - ala hold up the roof...the roofing, the insulation, etc. and carry those loads over to load bearing walls. That's called 'dead load'.
Now anyone with half a brain knows that service people walk across those all day long...that's called live load.
Generally some safety factor is used because people do stupid things in homes...but 'stacking weight' equivalent to two people at a point load is hazardous.
All beams deflect under load...so if you 'attempt' this recognize that your beams will deflect and apply forces greatest at the point of the load...the idea to spread the weight out across trusses is a prudent one (albeit foolhardy) - whatever beam you select it will apply the most force to the two closest and the least farther away. Which means a lot of loading at two points NOT DESIGNED to carry those loads.
Among other loads...are 'new roofing' (often 2nd layers of roofing are laid atop the old) - perhaps you already have tile...or composite...really irrelevant to additional loads only if a 'change' were to take place...also snow/ice/water loading...as well as wind and seismic loading.
So while it may 'hold it' it may not hold it under ALL situations and scenarios for which the structure was designed to perform...ala NOT COLLAPSE ON YOU when the 'weird' happens...such as some fatter service techs walking around...while there's snow/ice on the roof AND a car just ran into the building. So adding another 550-600 pounds (don't forget the members and attachment materials all add weight too)...or when an earthquake happens...or high winds.
Someone touched on in the comments the fact of the potential of a 'swinging load'...which is SIGNIFICANTLY greater than static loads.
MY ADVICE is to consult a STRUCTUAL ENGINEER - some calculations are beyond the 'simple calculators' which can be found online...there's more to structural engineering than just a 'beam loading calc'.
Edit: To include: That even your wall cladding (ala drywall or plaster) could also crack...not only do beams deflect but so do the walls that are under those roof pressures. Drywall isn't flexible...nor is plaster...so you may also have surface problems to deal with.
Edit2: I suspect you're wanting to hang a person...I hope in some sort of romantic/intimate manner and not permanently. I would recommend you transfer loads to the floor. As you didn't say what you'd like to hang...there are few things 350ish pounds that I can surmise beyond 'a person' (bsdm I presume). Reading comments you're on the 2nd floor with this weight...which adds to the center of gravity situations. You can reinforce the trusses too...remembering that the more cross sectional area the 'stronger' your reinforcing becomes. Best would be to calculate the deflection and have spacers on the trusses to allow for uniform loading with deflection. Without knowing what you're hanging - and for how long would determine how best to plan...a 'person' wouldn't be full time loading (I hope not anyway) - but still 'weird stuff happens' at unusual and unplanned moments. Also to consider...that home is designed to 'stay up' (for as long as it can) during a fire event...where loading would worsen that situation.
Edit3: A typical house is designed to carry 40 psf (pounds per square feet) live load...but that's on the floor. I believe rooves are 10 psf - but don't quote me...and WHY you should consult a structural engineer.
me-chewbacca OP t1_jefmiab wrote
Thank you very much for all your insights and detailed response. I really appreciate it.
Based on the comments in this thread and after confirming the type of roof I have, I gave up going ahead with this idea. It might be able to support it ok but I do not want to find out.
Someone suggested to transfer the load to the floor. One option I could see would be to support the 4x4/2x4 on two opposite walls in the room. I know the walls use metal studs and I assume it would need to lay on top of stud post that goes to the floor, not between studs. Anyway, I am giving up this idea for now.
By the way, the plan was to hang a Hammock Chair like this which would not be bearing the load 24x7. I also liked the "romantic/intimate" swing idea.... LOL.
outofmemory01 t1_jefxy7v wrote
The more you spread out the weight the better. BUT if it's only for a chair...then I wouldn't even begin to worry about this.
As I said...work men are able to walk across single trusses without 'damaging' the structure or loading. Therefore YOU 'sitting in a chair' is the same 'live load' for the area.
I WOULD do as you initially planned and span 4-5 trusses...use a beam calculator to determine the amount of deflection you'll get at each distance and use spacers/shims so you get equal loading to each beam. I'm 220# and walk across standard roof trusses with wild abandon...on one foot supporting all my loading. As I suspect you're equally heavy - and adding for chair and support you still probably wouldn't break a truss...but swing loading is different than static loading. So yeah...span 4 trusses have the outside trusses with like 1/2" spacers and the two closer ones with 1/4" spacers - that'll help spread out the load. As it's a chair it's presumed you wouldn't be loading it at the same time workers are also 'up there' (either roof or attic). Edit: Actually use a beam calculator to determine the correct deflection distances from the load - don't just run with the 1/2 - 1/4 I plucked out of no where. The closer you position to other vertical members the better - as everything 'works together' as a system.
Of course a hammock stand to the floor would 'spread out' the weight better...as that's got plywood as a load distributor instead of drywall - so you get more spread out loading instead of point loading.
I suspected it was a hammock chair...but it's more fun to be 'kinky' about it...but have also heard silly things like someone wanting to suspend fish tanks because 'it would look cool' - without realizing how much a lot of water actually weighs (and bodies being mostly water).
Anywhere you can spread out the load and transfer it more evenly to the ground is ideal.
I still would consult an engineer...only because were you to damage the home...or structurally impact it you'd need to declare (full disclosure) that in a home sale and/or insurance claim. Stamped calcs would clear you of 'reckless damage' (and other legal/financial risks).
As I said another option would be to stiffen up the existing trusses...usually done with slapping 3/4" ply on either side and through bolting (sandwiching the member). Stiffening won't 'solve' all the problems but will help transfer the loads to the walls and limit deflection.
Common safety factor is 2x and always plan for the worst...ala the potential of two people climbing in...the nicer thing about a stand is it becomes the sacrificial lamb instead of your ceiling/roof structure. You're unlikely going to cave in a floor any more than you would when two people hug/stand in the same spot.
Still engineering calcs would solve a lot of problems. I'd call one and find out the fee for it - it may be way less than you're suspecting - and determine how best to proceed. If the calcs cost more than a stand, get a stand...or if that would ruin your aesthetic and/or not fit in the ceiling height.
Giving up isn't a 'solution'...impossible only happens when you give up. You've got this...some things are worth the effort. Good luck and you're welcome.
Edit: I was the one that suggested transferring loading to the floor btw.
me-chewbacca OP t1_jegtdg1 wrote
Thank you for the info and the words of encouragement. Yes, I would still prefer to have it hanging than have it on floor. It allows me to put on or take it off to store it away when not in use. And of course, could also be used for other (kinky) applications, which is a bonus. ;-)
With that said, I'll see if I can find an engineer for such small job to reassure everything is ok.
Thanks again.
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