Replies

1. 
   piffin_ | Aug 09, 2001 04:44am | #1

   *
   Yes OK
   You don't mention the angle which I assume to be 45 degrees but if you go about a 7.25"/12" pitch you may find it more visually pleasing and less stark. Hard angles create a sense of conflict along with intrest. I try to use proportions that let you relax.

1. 
   Pro-Dek | Aug 09, 2001 07:50pm | #2

   *Your Joist size has nothing to do with with decking span, but has everything to do with joist span.Span your joists 8' Lay out your joists 12" o.c. if you plan on running your decking at a 45 degree angle because that equates to a 16" decking span. Bob

1. 
   piffin_ | Aug 10, 2001 03:29am | #3

   *but this is 5/4 not 3/4 deck stock.

1. 
   Jeff_Clarke_ | Aug 10, 2001 04:04am | #4

   *Doesn't matter - as noted the span is longer due to the diagonal. At 45 degrees it's approximately 1.414 x 16" or 22" @ centerline - a bit far for 5/4. At 12" o.c. joists it's 1.414 x 12" or 16.9" as noted.Decks are subject to 100 PSF loading here.Jeff

1. 
   piffin_ | Aug 10, 2001 04:13am | #5

   *Wow! Must be a lot of snow!

2. 
   Geoff_ | Aug 10, 2001 06:05am | #6

   *Jeff, are you saying you can't have joists spaced 24" O.C. and use 5/4 decking? , since 24"O.C. gives a 221/2" "clear span" and the 16"O.C. with diagonal decking gives the same span. Where are you located? Piffin,I think the 100 psf is for people load, not snow, i.e. big deck= large number of people on deck,hence 100psf loading req. Geoff

3. 
   Mike_Maines_ | Aug 10, 2001 06:18am | #7

   *100psf here too. I think the officials got tired of 3-story decks falling down.Mike

4. 
   piffin_ | Aug 10, 2001 12:15pm | #8

   *Well the live ;oad for a floor in living space is 40#. With appliances or pool tables, etc. that its fine. Are you saying that a deck outside needs more than the floor inside.? Good enough but the only rational I can think of would be for additional snow load. When I lived in Grand County in Colorado, the roof loads varied according to elevation from 40 to 110# if I remember right, because of snow load.The onlt other reason I can think of is for a commercial loading dock.

5. 
   Mike_Maines_ | Aug 10, 2001 02:24pm | #9

   *Piffin, my mistake, the Mass. code for decks and balconies is 60 psf. Depending on location, for roofs its 25-40 psf. In the licensing course I took a few years ago the instructor told us the reason for the high numbers was because during parties, people tend to congregate more densly on a deck than they would indoors. I bet designing for 60 psf wouldn't change the way you already build decks.Mike

6. 
   Jeff_Clarke_ | Aug 10, 2001 03:14pm | #10

   *i Are you saying that a deck outside needs more than the floor inside?No, the building code says that for decks and balconies due to notable collapses. Yes, it's people load.Jeff

7. 
   Geoff_ | Aug 10, 2001 05:59pm | #11

   *mike, you are right I just went back to check Ma. code, 60 psf, that's why I was asking Jeff where he was located, BTW, I'm in suburban Boston, where're you at? I remember the 3 story deck that fell a few years back that caused quite a ruckus around here. Hey Jeff, I was curious about the diagonal decking question, you say @ 16" O.C. joisting that a 5/4 deck board installed on the diagonal is "a bit far for a 5/4 board" refering to the span, but my response is ; isn't that the same as a 5/4 board spanning a 24"O.C. joist (perpendicular installation)? So does that preclude spacing joists @ 24" O.C. for a deck?(asssuming using 5/4 decking)

8. 
   piffin_ | Aug 11, 2001 12:43am | #12

   *Geoff, That was my main first point.Thanks for the redirect.As to the theoretical design requirement for parties, I will argue here not with you guys but with building codes and inspectors. If the concern is for high loads during parties - definitely important given the death rate connected - then the focus should be on total loading at the connections. It is my opinion that the failures occur at the junction of ledger to house or siding, not the surface decking that causes thesse failures. Mike, right on!

9. 
   Mark_H | Aug 11, 2001 02:15am | #13

   *Guys, I don't know if it makes a difference but this deck is only a few inches off the ground. So guests would probably survive a catastrohic collapse.

10. 
    piffin_ | Aug 11, 2001 04:31am | #14

    *Oh how we tend to ramble!All you are intrested in is whether the surface deck will be squishy. Right? I think that with 5/4 at 45 degrrees over 16"OC is plenty unless you are way up in the northern mountains or the snow off your metal roof is likely to slide and land with a thud. prodek isn't so sure.Build as solid as you can afford and you'll be forever happy.PT 5/4 isn't the best choice for surface decking tho'. Kids get slivers with chemical. It dries and checks in the sun. It doesn't look very good after a couple of years.IPE' is a far better choice for very little more money. Trex to but I would shorten the span or joist layout for it.but then again, I ramble......(*old age sets in*drops back off to sleep*snores*)

11. 
    Steve_Merrette | Aug 11, 2001 04:54am | #15

    *1.414! the square root of two, oh I just had a flashback to figuring RMS for electrical. ahhhhh thanks Jeff.

12. 
    Jeff_Clarke_ | Aug 11, 2001 02:11pm | #16

    *Central NJ here. The most spectacular recent collapse (last 3 years) was at the NJ shore. I don't know if your code precludes 5/4 decking on a 24" span but I would prefer 2x on a 24" span. Ask Bob (Pro-deck) what he thinks - I'd defer to him any day. Although, come to think of it I have designed a 15,000 SF multi-level deck with diagonal decking ...Jeff

13. 
    wildone_ | Aug 11, 2001 04:03pm | #17

    *Guess I am thick. Good discussion on deck building but I do not understand the realtionship to deck board span and deck collapse. Deck foundation and subfloor prevents deck collapse. When loads are calculated they are for posts, beams and joists. I believe that high deck failures are due to a lack of necessary cross bracing. With that said, there are a number of good references that provide guidence for deck spans. In all cases, they recommend that 2X6, all species, be used on 24" perpendicular and 16" diagonal spans. 5/4 Southern yellow pine is suitable for diagonal spacing @ 12" and perpendicular spacing @ 16". My reference for this is a recommendation table in the Taunton "Building and Design Decks" by Scott Schuttner. Pushing these recommendations will yield a bouncy deck that will appear to the customer and guests as lacking in quality despite the obvious visual appeal.

14. 
    joe_reilly_74 | Aug 13, 2001 02:31am | #18

    *Go 16" O.C and don't worry about it.

15. 
    Geoff_ | Aug 13, 2001 03:32am | #19

    *piffin, I agree with you, it is usually the connection at the house that is responsible for the majority of failures, you're right the inspectors, or rather the building code orgs. are the ones who promulgate these "overbuilt" requirements, i.e. 60psf framing requirements, when they need to address the attachment at the house specifically. It's important to either thru-bolt or lag screw the ledge to the house to prevent failures, nailing alone is just not sufficient. Geoff

16. 
    George_Lentulo | Aug 13, 2001 06:32am | #20

    *hey guys,Just my two-cents in form of a clarification to Piffin's post #14:TREX specs call for max. 12" joist spacing when decking is laid other than perpendicular to the joists. I mean, just in case you didn't know.George

17. 
    Jeff_Clarke_ | Aug 13, 2001 01:51pm | #21

    *Good points. The relationship is that of code requirement (based on i historicalissues of deck collapse) to span of decking. In other words 5/4 might cut it if the deck load requirement is low, but due to collapses and other issues the code requirement in some areas is higher. The higher the live load, the less a given decking material is sufficient over a given span.Subfloor?????Jeff

18. 
    Steve_Joyce | Aug 13, 2001 03:06pm | #22

    *piffen - I'm not sure what part of the country you live in, however the price difference for IPE vs. PT SYP in New England is significant. I agree that anything is preferred over PT pine however, the price can be prohibitive. I was quoted 3-4x's SYP cost for 5/4 Cedar decking when I was builing my porch. My lumber yard said IPE was roughly the same price as the cedar.SJ

19. 
    piffin_ | Aug 14, 2001 02:54am | #23

    *George, What I said but you more specific. thanks.Steve,This is true. SYP PT about $1.60 /SF - Fir about 2.50 - IPE about 3.00BUT -Learn to figure cost per foot per year of life expectancy.PT takes about ten years or less for folks to get sick and tired of the splits and slivers.Fir starts to go after about fifteen years.IPE is supposed to be good for 40. I doubt it'll be nice after twenty years but still functional. So if you figure cost per year, the IPE is cheaper.I'm on the coast of Maine so rot sets in quick. Working folk go with the PT about half the time. Upper class don't even look twice at it.

20. 
    Steve_Joyce | Aug 14, 2001 02:19pm | #24

    *piffin - it makes sense if you look at it that way. I interpreted your post to read that the initial cost were similar therefore making it an easy decision. For my porch I went with SYP for the flooring however for the deck that I will put in next year I am determined to use something else. The porch will get little exposure compared with a deck therefore it didn't make sense to me to spend the extra $. The deck is a another story, I'll see what prices are like next year.....anything but SYP & Trex would be nice.Where in Maine? I have an aunt in Ellesworth (?).A whole different world up there.ThanksSJ

21. 
    piffin_ | Aug 15, 2001 03:00am | #25

    *An Island in Penobscot Bay. I get to Ellesworth once or twice a year.

2. 
   Mark_H | Aug 15, 2001 03:00am | #26

   *
   I am framing my deck with PT 2x8s. I'm planning on running the PT 5/4 x 6 decking on the diagonal. Is 16" joist spacing adequate?