Replies

1. 
   frenchy | Oct 07, 2008 06:30pm | #1

   ben2h

     4 foot most assuredly will require posts. An easy rule of thumb is you can cantilever  the amount equal to your floor joists thickness.

     Mine are 8 inches thick so I was able to go 8 inches beyond the face.. (joists projecting out)..  if your joists are parallel Then it becomes much harder..

    There are also rules with regard to how far back the joists must project into the room. 

1. 
   FastEddie | Oct 07, 2008 06:46pm | #2

   frenchy, would it matter where the house is located?  And do you suppose an architect or engineer might be able to provide specific information about the cantuilever details?"Put your creed in your deed."   Emerson

   "When asked if you can do something, tell'em "Why certainly I can", then get busy and find a way to do it."  T. Roosevelt

1. 
   frenchy | Oct 07, 2008 08:51pm | #6

   FastEddie

    Sure absolutely! Note I gave nice safe numbers to work with?  If you wanted more you could but then things get really complicated. Four feet cantalevered? It's doable but not as an add on unless you're aware of something I'm not. 

1. 
   Piffin | Oct 07, 2008 09:03pm | #7

   I didn't catch the add-on at first, but it does seem implied "When I put on th e dormer"That makes it a whole other thing. He would need to rebuild yhalf the house to cantilever four feet if not engineered into it originally as it was being built new.Good catch there old man 

    

   Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!

2. 
   MikeSmith | Oct 07, 2008 07:18pm | #3

   ben...4 feet is a lot of cantilever for a floor loadmy BI would require a PE to spec itif you use posts then it becomes simple.... but it isn'l cantileveredMike Hussein Smith Rhode Island : Design / Build / Repair / Restore

3. 
   popawheelie | Oct 07, 2008 09:50pm | #9

   Another way to pick up the roof load would be to put some walls inside over the lower wall.

   Maybe wall that had openings in them with headers.

   Just an idea. I like combining different solutions to mix up design. It is more complicated though.

   Another thing. You could just cantilever certain parts. It would create more detail.

   Edited 10/7/2008 2:52 pm ET by popawheelie

1. 
   BossHog | Oct 07, 2008 09:53pm | #10

   "Another way to pick up the roof load would be to put some walls inside over the lower wall."

   Outstanding idea.

   That's one of the reason I hang around here - you never know what kind of creative idea someone is gonna come up with.

   What do atheists say when they have sex?

2. 
   mike_maines | Oct 07, 2008 07:28pm | #4

   Rule of thumb is 30-36 inches of cantilever is possible, more than that gets tricky.  When you add roof load to the outer edge it gets trickier still.  Gonna need an engineer for this one.

3. 
   Piffin | Oct 07, 2008 08:33pm | #5

   Anything over two feet requires special engineering.
   But it is doable. Can be cheaper to just set posts

   And there are special details if you use TJIs or open web floor trusses to consider also

    

    

   Welcome to the
   Taunton University of Knowledge FHB Campus at Breaktime.
    where ...
   Excellence is its own reward!

4. 
   BossHog | Oct 07, 2008 09:05pm | #8

   A 4' long cantilever is a long one.

   I use a general rule of thumb that you need a 1' depth for a 2' foot cantilever. So in your case that would mean a floor system that's 2' deep.

   A lot would depend on the width of your house, how the roof is framed, and your local loading requirements. It's most likely possible. But you would probably need an engineer to figure out what it will take.

   Why should I care about posterity? What's posterity ever done for me?