Can anyone tell me the formula to use for a cantilevered deck. The deck joists will be 2×10’s. I thought it was a two for one ratio. I have access to the existing house framing and can slide these 2×10’s in and bolt them to the existing floor joist under the floor of the house.
Discussion Forum
Discussion Forum
Up Next
Video Shorts
Featured Story
Performance improvements for the prized homes of an influential developer who wanted us all to be able to own one.
Featured Video
Highlights
"I have learned so much thanks to the searchable articles on the FHB website. I can confidently say that I expect to be a life-long subscriber." - M.K.
Fine Homebuilding Magazine
Fine Home Building
Follow
-
Fine Homebuilding
Dig into cutting-edge approaches and decades of proven solutions with total access to our experts and tradespeople.
Start Free Trial Now -
GBA Prime
Get instant access to the latest developments in green building, research, and reports from the field.
Start Free Trial Now
- Home Group
- Antique Trader
- Arts & Crafts Homes
- Bank Note Reporter
- Cabin Life
- Cuisine at Home
- Fine Gardening
- Fine Woodworking
- Green Building Advisor
- Garden Gate
- Horticulture
- Keep Craft Alive
- Log Home Living
- Military Trader/Vehicles
- Numismatic News
- Numismaster
- Old Cars Weekly
- Old House Journal
- Period Homes
- Popular Woodworking
- Script
- ShopNotes
- Sports Collectors Digest
- Threads
- Timber Home Living
- Traditional Building
- Woodsmith
- World Coin News
- Writer's Digest
Replies
most decks can not be cantilevered.. in a lot of locations the code loading is 60 lb/sf
at that rate you MIGHT be able to cantilever about 2'
also.. it is almost impossible to cantilever without making numerous penetrations that will leak and rot out the framing.. there is practically no detail that will prevent this
others may have different opinions... but these are mine.. forget about cantilever
Mike Smith Rhode Island : Design / Build / Repair / Restore
"2 for 1 ratio..."
Generally, rule of thumb is that a cantilever should not exceed 1/3 its total length, so you are correct. ( ie...to cantilever out 6 ft, you need a joist whose total length is 18 ft; of which 12ft will be attached to solid anchoring and the remaining 6ft will be hanging out...hence 12ft vs 6 ft = 2 to 1 ratio).
But, for conservative floor loads, it would be better to calculate your cantilever to not exceed 1/4th its total length instead. ( ie... to cantilever 6ft out, use a joist 24 ft long).
If you plan on cantilevering farther out than 6ft using a 2x10, I'd definately get a structural engineer involved or rethink my deck design altogether ( ie...install a few support posts underneath the joist deck span).
Davo
davo.. you also have to allow for strength of materials.. ie: what is the breaking strength of the 2x10... this is usually the limiting value in a deck cantileverMike Smith Rhode Island : Design / Build / Repair / Restore
First, what will the finished elevation of your deck be? It doesn't affect the load calculations but it lets you know how close to max tolerance you want to get. Why not just sink a few posts, it really doesn't take much effort, and using a couple of posts with shorter joists will probably be less expensive than using 24' joists just to get 6' of deck.
What does your building code say for cantilever? Here for a 2x10 x is 24" of cantilever alowed. Also the rin boards are figured into the cantilever length. 2x8 you can have 20 inch of cantilever.
For a longer cantilever you need to hire a engineer to sign off on the plans.