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Question DetailsAsked on 5/20/2018

Can I hang a hammock off of the 2x8 collar ties in my screen porch?

I'd like to hang a rope hammock in my screen porch. There are 2x8 collar ties across the width of the screen porch roof rafters. I used straps to hang my hammock diagonally across two collar ties. It seems to support the weight but it generated a sideward pull on the collar ties so I took it down. (1) Is it safe to hang the hammock from across the collar ties if I sister them so that they are now 4x6? or even 6x6? (2) Is sistering the collar ties a good solution to strenghten the collar ties?

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2 Answers

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Foloowing is NOT structural design or advice - just what I personally would do if same situation at my house.


Hard to see exactly the length of your collar ties from here, how they are fastened to the rafters, how long your hammock ropes are and what angles they are pulling at and such - but sounds like you were hanging between collar ties so you were pulling transverse to them - in the weak direction, causing them to "bow".


If they are just nailed directly to the rafters I would not trust it to carry the load - personally I would get the proper SImpson structural plates (right ones for the member sizes and angle of intersection) to fasten the ties to the rafters, using Teco nails or structural screws, to be sure they can carry that vertical weight safely. (Collar ties are designed as pure tension members only - not designed for vertical weight loads). They may already have the equivalent in plywood joiner plates nailed to the pieces at the intersection - if substantial (say 1/2" or thicker) plywood on each side with screws and 10d or larger diameter nails, give it a good test but likely will be fine.


As for the bowing - run a continuous stiffener piece across the top (so likely 10-12 feet long if one piece) of the collar ties, nailed into the tops of them and roughly in line with your hammock location, to prevent bowing sideways. If a long run you could use two offset by board width to use shorter boards to fit in your car - running one from the first supporting collar tie to one near the middle, second one from there (side by side with the first brce) to the other supporting collar tie. To get proper fastening use structural (NOT drywall) screws pilot drilled through the brace if say a 1x4, and use washers to prevent splitting. If using a 2x4 straight nailing with a couple of 16d nails or 3-4" #10 or larger screws at each collar should hold it. Nail or screw at each collar you cross with the stiffner to prevent IT from arching up under load, and so all the collars will share the lateral load from the hammock suspension ropes - because remember at normal low angles they are putting maybe 3-7 times the lateral load on the supporting end as the vertical weight they are carrying - that is why the 2x8's bowed so readily under what you were thinking was just a 200# load.


The brace between the collars effectively makes a structural triangle between the hammock ropes (as two sides of a triangle, albeit somewhat rounded in the middle where the hammock is), with the bracing piece being the third (compression) side of the triangle - taking the lateral load off the collar braces.


I wouldnot sister the ties - probably overkill, plus the extra fasteners at each end (unless using proper structural plates) would put too many fasteners into the rafters and might cause splitting of them. Plus unless you did it at every one would look funny.

Answered 5 months ago by LCD

0
Votes

On the bracing - while #8 screws or #12 nails or so might do the job, and maybe even 2x2 for the bracing, between keeping it from bowing between the collar ties and not splitting at the fastenings, probably using 1x4 or 2x4 for that reduces those issues. Could be fastened into the collar tie top or bottom as desired (because it will be acting in pure compression) - just not real near an end where it might cause splitting. Preferably on the face the hammock load is pulling at - so if pulling off the top of the tie, put brace on top - if pulling around the bottom edge or from a bracket hanging down from the tie, brace would better be on the bottom of the tie to prevent warping/bowing - though since we are talking short-term loads (only an hour or few at a time) long-term warping of the tie is not a consideration like it would be if heavy planters or such were being suspended from a rope of cable between them.

Answered 5 months ago by LCD




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