Cantilevered deck joists – span limits
Hi,
I’d like some advice – especially from the framers/structural engineers in the house 😉
I have a second story balcony that was built by someone else in 1975. It has 2×8 southern pine floor joists 16″ OC cantilevered out 6′ from the building – no beam underneath. The deck is 6′ x 16′. I suspect (but can’t confirm) that the joists extend at least 12′ into the structure – maybe more (but just how long did they make 2×8’s in 1975 anyway?)
I’ve ripped the redwood 2×6 decking off these joists in preparation for a Trex install – the 2×6 boards (not 5/4). The dead load difference is likely negligible, as the redwood on the deck was pretty dense. I’ll be adding a Trex pvc railing system as well. Again, it’s about the same weight as the 70’s balustrade that used to be on the deck.
I can’t believe 2x8s 16″ OC can support a 6′ cantilever. Most codes say 3′ max, possibly more with a 3:1 ratio of cavtilever to buried joist. Before the demolition, the deck was not noticeably deflecting, but we’ve never had more than 4 people on it.
THE QUESTION IS THIS: Should I be cutting the cantilever length down? Leaving it as is and posting load limit signs (suggested on another thread 😉 Adding support underneath is not an option and I’m really not interested in doing cables to the upper structure. Just how “off” am I with this span?
Thanks in advance for any advice.
J
Replies
Do I understand you correctly....you will be putting new 2x6 Trex as the deck surface? If so the weight difference between Trex 2x6 and Redwood 2x6 is considerable, why not use the 5/4? The 5/4 is still heavier than the Redwood , but not as heavy as the 2x6 Trex.
Second I'm not sure Trex railing (4x4) posts meet lateral load requirements for rail systems, I'm not positive though, but I'd check w/the B.I. first.
I think you need an engineer to do a load calc just for the Trex loading anyway, since it is much heavier than redwood, and although it's been O.K. for 30 yrs. your better safe than sorry,since it sounds like you want to put "more than 4 people" on it.
Geoff
Geoff,Thanks.I'm using the 2x6 because of my tendency to overbuild - and I don't want any sags. The material is in my garage, so basically a given at this point.The rail is Artisan Series - which will use 4x4 ACQ posts with composite sleeves arond them, so I believe I'm good on the rating there.Yes, I guess an engineer is in order, but was trying for some quick reads on this...Jim
""(but just how long did they make 2x8's in 1975 anyway?)""
Oh I think they made them all year long back in 75.
;-)
I would never build it that way myself.
But you say it has been in service without noticeable deflection since 1975! Time and service tested means something!
The big Q other than structural engineering is whether rot has made any ingress and how bad the water being drawn into the building envelope has damaged things inside the wall.
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