I’m working on a deck design and I recently downloaded a freebie software to help design a deck. It asks about basic shape, rail, benches, etc and then produces drawings and a material list list. All very nice except it offers no engineering suggestions on the size and spacing of joists. It just asks what size and spacing you want. So where do you go for answers to those questions? By the way, I’m in an area that has no building regulation so I have no gov’t agency to consult. Also I am planning to build the deck as free standing with no physical attachment to the house although it will appear connected. The deck is on basically flat ground at the height of a doorway about 2 feet off the ground. My thinking is that it is just as easy to add a couple of piers to the plan as to undo the siding and install a ledger board and risk water penetration into the house structure. Any thoughts on that?
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Go to your local library, they will have plenty of books on decks that will include tables for all your engineering. Failing that, I think Decks.com has a decent web site for that type of info.
I tink a freestanding deck is always a good idea. Especially if your not certain of the correct way to flash a ledger. Just remember you have to sway bracing in two directions.
Edited 3/12/2008 1:44 am ET by Ryan12
freestanding is most definitely the way to go. Sway bracing probably won't be that much of a concern since you're only 2' off the ground as long as ou have enough posts and they're deep enough.
Thanks for the help. I did find the decks.com site one poster suggested and learned that I need 2x8 on 12 or 2x10 on 16 for the span I plan. I haven't checked expense yet but I'm thinking about the 2x8 on 12" option which would reduce flexing in the deck boards. I've heard this can be a concern with composite deck boards. As to the freestanding vs ledger board issue, I'm still leaning freestanding. My house siding is vinyl so I won't rot it. A little maintenance to make sure the small gap doesn't get clogged with leaves should protect the rim joist and putting in a couple of extra piers with a girt looks simpler than attaching a ledger board and flashings.
I am in the process of doing just what you are asking about. You need to fill out your profile or at least say where you live. I live where the frost line is supossedly 12" but frost heave here is pretty non-existent if you have reasonable drainage. I used 12x16x4 precast as footers.
If free standing and not attached and under 30" high there is no permit req in my AHJ. I did this one to the 100 p/sqft and then doubled every other joist in an area BIL said he may want to put a hot tub.
A city/county east of here had a pretty good brochure on design but they must be redoing their site and I could not bring it up to link.
http://www.hammerzone.com/archives/decks/basicp1/build6x6.html
Edited 3/13/2008 12:38 am ET by rasconc
Edited 3/13/2008 12:40 am ET by rasconc
I'll have to disagree with the others. If your house already has a foundation, then why build another for a structure you want to stay in plane with the first floor of your house? How deep do you need to dig for the piers to be below frost? Will this undermine your house foundation or interfere with drainage or insulation?
Removing a course or two of siding is not a big deal, and proper flashing or spacing from the rim joist will prevent any moisture problems.
As far as sizing the joists, unless the deck will experience significant live loads (from people dancing or snow dropping off the house roof) you can use conventional span tables for a first floor (the deck framing will be stronger if it's built with PT SYP).
If you tell me the size of the deck and the span and type of wood of the joists, I can give you the information you need, as I engineer all my own framing systems and teach engineering for the home-builder.
Drip cap and counter flashing:
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Spacers (wood or steel washers)
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Solar & Super-Insulated Healthy Homes
Edited 3/12/2008 8:17 pm ET by Riversong
I owned a house once that the previous owner had gotten creative with and ran siding behind the deck ledger, probably to avoid water penetration. Would have been a good idea, except that the siding rotted and had to be replaced--nothing to do but tear the whole deck off. I agree that attaching it to the house with a conventional ledger is the way to go.
Many city's building departments publish info on deck engineering. For example, check out http://www.duluthmn.gov/city/bsafety/general/Decks%20Packet%202007.pdf.
AGtax
You can go to this site to design your own span.
http://www.awc.org/calculators/span/calc/timbercalcstyle.asp?
I did a calculation for 2x8 southern yellow pine and the maximum span was 12' 11", with 16" spacing.
Rich