Can I Cantilever An Extension To An Existing Deck?

lot249

The original deck construction was restricted in size leaving the deck 5 feet short from its ascetically ideal width. The length of the deck extension is 16 feet. (desired extension is 5'x16').
deck extension.doc
The deck is 5 feet from the ground. The concrete base to which the support bracing would be anchored can be no closer then 5 feet from the end of the extension.

The first question is can this be done with sound structural integrity?

If yes, at what angle would the support bracing need to be to securely support the deck extension?

See attachment.

Any feedback and suggestions would be appreciated.

Thanks.

Anti-wingnut

By the looks of your diagram, the answer is no. Now prepare yourself for flaming.

greg24k

Getting comfy

Attached Thumbnails

 

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naptown CR

Speaking of flaming I live in Annapolis and this is commissioning week at the naval academy ( graduation) The blue angels do a show every year during this week. The show is tomorrow but today is practice day and it's like two shows as it goes on for longer. To make a long story short I jut had two of them fly over the house at probably 400 knots at 300 feet and kicked in the afterburners. I love that sound, sounds like victory. If you have never seen one of their shows it is definately worth it if you're into military aircraft. Haven't missed a show in 15 years I've lived here. Will launch boat tomorrow and sit in the river where there are no trees to block the view.

Back to OP as drawn no will need engineering and a lot more detail at the least. Is there a pool at the end of this and you want to create a diving board? This is what you have drawn.

JamesKB2

That's what I thought too, pool, over a lake edge, or something like it.

I looked hard at it, only thing I came up with was to sister joists to the original structure 3:1 (meaning, 5' addition requires 15' or better length), add another load bearing header under the addition at 12 to 24" max cantilever, so now you have two load points, the original, and the added, with 5' of span between them (assuming the original is cantilevered 12 to 24") Run ANOTHER load bearing header to carry each AT POST SUPPORT and angle brace back to post from that. So, looking at it from the side, you have a U shape with angle brace from bottom of U at new header point. The angle brace would be sandwiched in between (2) 2 X 10 or 2 X 12 treated stock.



EDIT: My drawing was a quick throw together, the angle brace would be cut to meet flush with the bottom of your new vertical header, (this side view) running in between the horizontal header. Also, it should meet the post as close to grade as possible, and be cut to fit the post. I would also ADD posts to this, under the existing header. If you have 3 posts, make it 7, 4 posts (should) make it 7. Angle brace of same dimension as your posts. I might even sister up flanking members on the angle brace cut to fit under horizontal header, run past posts and cut flush on backside of post. I would consider through bolting the horizontal (this side view) header through angle brace and post. Two through bolts at header, one at post. If they're 4 X 4's, be careful you don't create a breakaway post by removing too much material with a through bolt. It's dicey, I would consult with an engineer for sure.

All I could think of.....

If there's a way to do it, safe and longevity of use, I'd be interested.

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I will build you whatever you want, just draw it on the back of a big enough check.

B.K

Can you a "Master Cabinet Maker" cantilever an extension to an existing deck?

No.

For some real advice, when dealing with structure and not really knowing what to do. It sure is a lot better if you spent the few hundred bucks on an engineer, instead of trying to get a sweet answer on the internet (although I'm very sweet, also I'm not allowed to work in the rain because of that )

-Bill

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Anti-wingnut

Your design is poor. The beams parallel to the sheet do nothing. The knee braces do all the work, so why add the beams?

JamesKB2

Thanks, 'preciate the comment.

The horizontal beams are in place to carry the new full length header. I suggested to the OP that 7 load points be established across the 16' of deck length by adding posts if required.

Since the load will want to deflect the end of the deck down, with a simple angle brace the deflection would cause the brace/header connection to roll (knuckle point) By using a header (the horizontal one), you can support the brace and also eliminate that. It also ties the existing post / header to the new one, creating a lookout. If you've ever set up a lookout, to place planking on for elevated work you know they are quite strong.

I don't think it's poor, I would certainly have an engineer consider it, or an alternate solution. What you propose (no tie to the post and new header supported by angle brace only) is weaker than what I have.

HSConstruction

add another girder its the only way. Otherwise you will have a 5' cantilever plus the original cantilever. A 6-7' overhang will fold like a bad hand in poker.

Even if you could get a joist to hang 7', if the deck is narrow the teco hangers would need to be put on upside down to resist the leverage of someone or multiple people standing out there.

Your free answer is NO. But an engineer may have an expensive solution.

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KennMacMoragh

The way you describe what you're doing is a little too vague. I can't tell how you want to cantilever it from your description and drawing. If you asked if there was a way to make the deck bigger, then yes there's almost always a solution. But we would need more details as to what the existing house looks like.