I want to extend my deck 12x16 to 12x18. What is the easiest way to widen the deck by 2 feet from a structural standpoint? How do I go wider than the beam?enter image description here

  • Assuming the Length of the beam is the width of the deck, You’re gonna need a longer beam ! Not much more we can tell you until we have more information. A photograph or a drawing of your current deck would be helpful. – Alaska Man May 16 at 23:44

I’d remove the last two existing joists (joists furthest from the house) and reinstall them next to the third joists. I’d fasten them together with 1/2” thru bolts at 8” o.c. Staggered 16” o.c. Top and bottom. (Install them 3” from the top and bottom

Then I’d install a 4x12 across the end of the deck (extending it to the existing width at each end) and align the top with the top of the existing beam. I’d fasten it to the existing beams with Simpson GLTV beam hanger (installed upside-down) at each end. (Be sure to order it the correct depth based on your existing joist depth.)

Then I’d install the same size joists as the existing joists and cantilever them 2’ to gain the 24” you’re requiring. I’d install solid blocking between the new cantilevered joists and clip each joist to the top of the new beam with a Simpson A35. I’d use Simpson “U” Series for the connection to the 3-sistered joists.

Then, I’d reinstall the diagonal bracing.

Extend existing deck covering as required.

  • Why would you install the GLTV hanger upside down? You typically only do that when the uplift is significantly greater than the vertical load. The dropped 4x12 doesn't have any uplift on it, only the 3 ply beam and cantilevered joists will. – Dotes May 17 at 3:16
  • @Dotes The new beam is being supported by the existing beam, therefore the existing beam needs the steel plate on top of the existing beam. This beam hanger is designed for the continuous beam to support the existing beam. – Lee Sam May 17 at 3:46
  • Can you extend the beam by adding two more .2x12 and let it go by the two feet, and add a 4x12 filler bolt together. add a short peice at house lag in a use joist hangers.Let the 2x12 run whole way to have good attachment for cantilever..Carry your layout through and you may be able to use the outside joist over. – user101687 Jun 16 at 17:25
  • @RobertMoody What does, “add short piece at house lag in a use joist hanger” mean? And, what does, “Carry your layout through and you may be able to use the outside joist over” mean? – Lee Sam Jun 16 at 18:00
  • Not sure how it is framed to house add to ledger add the two feet needed .Lag bolt it to the box or studs. add joist hangers there if needed. The joist are 16 on center or 24 .Keep the same layout if you add joist. Reuse the outside rim joist if in good shape. – user101687 Jun 16 at 19:08

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