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denemante 10-09-2012 12:50 PM

deck addition - possible?
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Hey all,

I'm considering a deck addition as shown in the attached illustration on the left side.

So per the illustration "question point" - the side of the original existing deck (far outside left joist) is a 2x10.

Could I attach deck hangers to the outside of that , and run new joists perpendicular and out to support a new section?

Alternately, I could actually add a third new leg (not shown, it would be in the lower right corner of my new section) - then run a header from it to the outside left edge of the top/left leg of my existing deck, bolted through.

AndyGump 10-09-2012 02:59 PM

you could just build it free standing, not attached to the other deck at all.


GBrackins 10-09-2012 03:37 PM

if you are looking to attach new joists 90 degrees to an existing outside joist I think you may find the existing joist will be not able to support the load. You would need to create a beam of sufficient size to support the new imposed load.

Read through this and it may aid you. It is the American Wood Council's "Prescriptive Residential Wood Deck Construction Guide."

post back with any questions.

Kissfan4 10-10-2012 12:06 PM

if it was me, i would build it freestanding. If you are worried that i may move a little and see it separate while on the deck, build it freestanding and bolt the new joist to the current. if that makes sense

denemante 10-10-2012 02:09 PM

This project started as a little platform to house my grill. So perhaps 2 feet out and 4 feet wide. Then it grew into what I've described.

If I just wanted a little 2x4 foot rectangle hung off one side of the deck, could I cantilever it out somehow, or would I really be talking about the same thing?

GBrackins 10-10-2012 02:53 PM

check out Figure 1A on page 3, and Table 2 on page 3 of the "Prescriptive Residential Wood Deck Construction Guide" that I provided a link to in post #3. You can figure out based upon this how much you can cantilever your deck.

Good luck!

KevinPh 10-11-2012 08:20 AM

From your drawing, it looks like there is nothing to cantilever. If you were going to cantilever it, it would extend out in the other direction from where you want the deck addition. According to GBrackins link, it looks like the code says that the max. extension for a cantilever is 1/4 of the joist span. However, the building code in your area may say different. Where I live, the max. cantilever is 24 inches. Here is another link for cantilever info ...

You show that you would add two new posts on your drawing. I would install a third post adjacent to the top of the stairs and use the existing one in the top left hand corner as the fourth - then you will have a box-like structure to build the deck extension. You could run your decking and joists in the same direction as the existing. Might want to check with an engineer or deck builder on this one.

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