I want to demolish and rebuild a second story deck. The customer wants composite or plastic decking for sure. Optionally, he wants the framing replaced. 16′ 2×10’s@24″ o. c. hanging from a ledger on the house on one end and cantilevered 2′ over a 6×10 beam which sits in a beam pocket or hanger on the house on one end and cantilevers 2′ over a 4×6 post, which bears on a 12″x12″ precast pier block. The new framing would have the joist spacing reduced to 16″ o.c. to allow more options for decking material.
This has held up fine for 30 or so years and passed building inspection when new, but how would you verify that footing, post, and beam size would be adequate? We’re in the Seattle area.
Replies
Firstly, I AM NOT an expert on deck building. There is a guy in Seattle, called Pro-Dek <http://www.prodek.com> who used to post here a lot - before he had intersting stuff happen this summer. See if he can help you.
I have found that composite decking feels better with 12" OC. Even 2x10, at 16' seems a little light to me.
I'm not sure about the footing post size either. Around here I use 24x24 pier blocks when I have to, but I'll bet the code has changed since your system passed 30 years ago. We are FAR more aware of earthquakes nowadays.
Quality repairs for your home.
AaronR Construction
Vancouver, Canada
aaron.. saw your reference to ProDeck... is Bob alright ?
miss his smiling face ...Mike Smith Rhode Island : Design / Build / Repair / Restore
I have no idea. Last I heard was May of June and nothing more since then. I sure would love to see more of his work again, too.Quality repairs for your home.
AaronR ConstructionVancouver, Canada
Hire an engineer. Then you'll know for sure.
Ask the bldg. dept. in your town, they will know for sure and it will be a lot cheaper than an architect or engineer. depends mainly on how far down the frost reaches.
If you ask our building department, they'll tell you to get an engineer's wet stamp on dwgs. Check by phone with yours.
-- J.S.
Most Building Departments around here have handouts that will help you in sizing your footings and beams, joists, and etc.
Goes to show you how different towns operate, I can walk into mine and they can answer almost anything on the spot. No engineer neccessary.
http://www.riversideca.gov/planning/building/DRAWINGS/Patio-Cover-Requirements.pdf
Here is an example.
Jack
You don't really say the size of the deck (lenght?) so I doubt that anyone can really answer the question. Really though, why would anyone want to install (and pay for) 50 yr decking on framing that is likely nearing the end of it's life expectancy?
You are on the right track in saying that the 2x10 @ 24 O.C is not adequate support for composite decking.
Re post size that is as muych a function of the height of the post as well as the load.
As far as the footer size, we don't know what type of soil your are building on, so again, it would be difficult/imposible for anyone to give a qualified answer. To get started though you need to figure the tributary area that each post and footer supports. I can tell you how to figure this is you give some more info other than 16' joists with a 2' cantalever, like the length of the deck, the number of posts and weather the end posts are right at the end of the deck, etc. It almost sounds like the deck is supported on 2 sides by the house? and there is only 1 support post?
That's right. The deck is supported by the house on two sides. I thought I'd add a post and pier 2' from the house. Then the beam would have 2' cantilevers on either end and a clear span of 10' 3". A 6x10 would then seem like overkill.
Forgot to mention the width of the deck (length of the beam) is 15' 3".
Attached is a quick drawing designed to make you think...
In the drawing, the load on the post is OK but and footing load is probably quite marginal depending on your soil type. This load is around 2700 lbs at a 40 PSF design load. OTOH the beam is definitely over-spanned. Also, I would hope that the beam connection to the house is pretty strong since it is also carrying roughly 2700 lbs at the 40 PSF design spec. BTW - 40 PSF is quite minimal. Some jurisdictions go with 60 PSF.
If I were building the deck from scratch, I'd probably use 3 posts and not even attach the deck to the side of the house that the joists are parrelel to. Attaching to that side just gives another area for water intrusion and doesn't support that much weight.
drawing is attached to next posting
Edited 9/15/2005 10:25 pm ET by Matt
see attached
Thanks, Matt. The drawing makes sense and is sort of like the deck I'm talking about. The post is located at least 2' from the end of the beam. I just don't know the rated strength of the 6x10. I'd add another 6x6 post and footing 2' from the other end, shortening the clear span of the beam to 10'-4". Right?
If the homeowner decides to go ahead, I'll let the plans examiner correct my design.