Replies

1. 
   Jon_Mochizuki | May 08, 2001 03:49pm | #1

   *
   Louis,

   The span tables are usually tabulated for a uniform live load, typically 40 psf for floors and decks. If you assume you have about 16-inches of soil at about 100 pcf, you have about 140 psf on the deck, plus maybe 10 psf for the deck, planter weight and planting itself for a total of about 150 psf. For this weight and span you should at least sister the 2X12's. Depending on the grade and type of lumber, you may even require 2-2X14's. With 2-2x12's you'll also have about 0.6-inches of deflection. I suggest you get an engineer to figure something out for you.
   Jon

1. 
   John_Sprung | May 08, 2001 07:48pm | #2

   *As I read this, the planter will be almost as long as the joists, and parallel to them. Rather than opening up the deck, why not make the planter a single structure supported only at the far ends? If you can make it 16' instead of 15', it can be completely independent of the joists. The sides could be truss assemblies that could be pre-fabricated, and then bolted together on site. This way, technically the planter isn't even a part of the building, it's just a flower pot sitting on the deck -- a very big flower pot. ;-)Of course, any time you put any kind of plant on a wooden deck, problem #1 is constant wetness creating ideal conditions for dry rot and termites in the deck.BTW, what city is this in?-- J.S.

1. 
   Trent_Baughn | May 09, 2001 02:53pm | #3

   *Apparently there are two threads on this subject.I think Mr. Sprung has hit the nail on the head. Making the planter an independant structural element is an excellent idea, assuming the end supports can handle it. The trick will be to design it in a way that it is constructed of 'shorter' members, thus rleiving you of your crane problem as well.

1. 
   Boss_Hog | May 09, 2001 10:42pm | #4

   *Are these things really fire treated, or just pressure treated ???

1. 
   Louis_Brandt | May 10, 2001 05:25am | #5

   *Yes, there are two threads posted on the same problem, my mistake. To reply to Ron, yes they are fire-treated. In reply to John and Trent, the planter will be an independent structure that sits on top of an existing deck. I can't make a 16' truss assembly because of the problem of getting it to the 7th floor roof. The deck itself is 6' above the roof, such that it clears the various mechanicals. The 2 x 12 joists rest on steel I-beams which must be 12 or 14" high, I didn't measure them. I was wondering about splinting (2) 2 x 12 x 8' boards, joining them with something like a 4' long by 1/4" or 3/8" steel plate and 1/2" bolts and then lag bolting this on to the existing joists. Everything is accessable from underneath. I want to re-inforce the 3 joists that will be under the planter. Will this work?

2. 
   Boss_Hog | May 10, 2001 12:30pm | #6

   *The reason I asked about fire treatment is that the stuff I've worked with can't get wet. Don't know if that's true of the treatment type you're using, but you might want to check it out.

3. 
   Ralph_Wicklund | May 11, 2001 02:45am | #7

   *As I read, I'm still not clear as to how you will be getting your material to the roof deck. Are you planning shorts so it all fits in the elevator or are you carrying it up the fire stairs or are you winching up what you need. With a little planning for the safety aspects of the job there should be no problem, as someone has already posted, with winching your material up the side of the building from the alley (if there is an alley).Parallel chord trusses could be used as the sides of your planter and sheathed with a thinner material. Plan those trusses to be long enough to be supported by extension from the main steel beams on either end of the deck. Even though a parallel chord truss may be 3 1/2" wide, and a pair of them would be used for the planter, the size of the planned planters might benefit (esthetically) by a more massive look than just what I visualize to be a rather skinny trough perched on the edge of the deck.But, if you can't, then I see a little sistering in your future and maybe a little solid blocking, too. And don't forget the fireproofing that will be required when you add to the existing joists and perhaps you should consider a PE who can nail down the optimum bolt pattern and length and number of sistering members you will need.

2. 
   Louis_Brandt | May 11, 2001 02:45am | #8

   *
   I am building a number of large planter boxes for a penthouse deck. The deck is elevated above the building roof. The joists are fire-treated exterior 2 x 12's, 16" O.C., running a 16' span. The planter will be 37"d x 28"h x 15', running parallel with the joists. One section of the planter (appx. 3'w) will be filled full depth with soil for an ornamental tree, the rest will have a raised bottom allowing for 16" of soil. The owner is concerned about the additional weight of the planters on the deck and wanted me to put in additional joists. After a site visit for measurements I realized that the only way I would get a 16' 2 x 12 to the 7th floor would be with a crane. So, I need to know if the deck will support the weight. I have found span tables at some of the industry trade association sites, but not load tables. Any ideas?