I have a elevated deck (~8ft) attached to the back of my home, and I would like to add about 5 feet to it. What is the proper way to add this extension?

I want to extend further away from the home. For example:

Home -> DECK -> Extend This Way

  • Extend which way? Further out(wider) from the house or adding on to the end and having it longer along the house. Further out from the house will require a new beam and posts at least. It might also require a complete rebuild of the deck if code as been changed since the deck was built.
    – crip659
    Commented May 25, 2023 at 13:19
  • @crip659 - see my edit - does that make sense? I want to extend it away from the home more. Basically it goes 5 feet "out" away from my home, and I'd like to make it go out 10 feet Commented May 25, 2023 at 13:24
  • 1
    Please add pictures of your current situation. Without pictures and knowing how your current desk is constructed and what your situation looks like, no one can provide any advice.
    – Milwrdfan
    Commented May 25, 2023 at 13:44
  • @Milwrdfan - ah sorry - i didn't realize images would be needed. I'm at the office atm, but will upload some soon. Commented May 25, 2023 at 13:48
  • What is the elevation off the ground? Commented May 25, 2023 at 13:59

2 Answers 2


Depending very much on your Local Authority Having Jurisdiction, you might or might not need permits, plan approval, etc. and in most cases getting that part sorted (if required) will automatically force you to get competent advice on the next bit...

Which is how you hold it up - that depends on the shape of the land, the type of soils or bare rock or whatever you have under the proposed area of the new deck, the height of the deck, the local snow, wind, and seismic loadings required, frost depth if applicable, as well as design requirements for the live load of people being on the deck, and how the current deck is held up.

Doubling the size of the deck will be enough of a job that you should look very, very carefully at the state of the current deck to determine if remove and replace actually makes more sense than preserving the old deck and extend with 50% new.

  • Getting engineering is a good idea regardless of AHJ requirements. It's easy to make mistakes like extending deck can increase live and dead loads on existing supports. Commented May 25, 2023 at 19:11

The most common will be new pressure-treated posts into the ground or connected to a concrete footer for the extension and probably posts and a new rim joist added to the existing structure. That way you aren't really adding stress to the old structure. 4x4 if low, like right off the ground, 6x6 if in the air, 8x8 if up past six feet. The rest is just boards to join the posts and hold the deck boards.

I leave to you permitting, etc. if required.

  • this is what I was after. I have no problem putting the posts in the ground, but not certain on how to frame it out with the joists etc. Commented May 25, 2023 at 16:42
  • @user2676140, steel supports are the most trouble-free. Lag bolts work well.
    – Tiger Guy
    Commented May 25, 2023 at 17:55

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