[boddah]

what the most i can make an extension on the deck using 2x8s? can i do 3 feet at least?

 

[Scuba_Dave]

What do you mean by extension & overhang?
You want to overhang 3' without any support below?
I don't think 3' will work

 

[joel v.]

Do you want to add 3' without support or are you building a new deck and want to know how far you can extend a 2x8 past the beam. For the first one you would have to put new 4x4 posts in the ground and new beams across and extend you deck that way. If the second one, it depends how how your deck is. If you have a 20' deck you could likely make 15' fully supported and 5' over hang provided that it's all one 2x8. On our deck it hangs over the beam about 3' with 2x6 joists and there is no extra movement.

 

[boddah]

the overhang will be past the 4x4 posts supporting the original deck. it will be made of 2x8 joists that are 3 feet long and will be atached with joist hangers to the deck and to the new end which is also 2x8. will this be strong enough for the 3 ' overhang or is it possible to go further like 5' like joel said

also you can feel people walking on the deck when you are sitting and is a little bouncy or shaky feeling. the current structure is 22' long and 20' wide. there are 4 4x4 post at the 12' point and 4 4x4 at the end. the joists are 2x8 and are about 20-22" apart.
any ideas to beef up the structure to make it feel more solid?
thank you guys for your time

 

[Scuba_Dave]

I never go less then 16" OC for a deck
I overbuilt mine & went 12" OC
If the existing deck is bouncy then it is underbuilt
Not sure if you can add another joist in between the existing joists

If you are adding on 3' & hanging the new 3' joists off of the existing deck then you need support on each end :huh:
Joist hangers will not allow you to hang these in the air ?? :blink:

 

[boddah]

ok so a few more joists will strengthen the deck? i knew it should have been 16" oc

i need a support on either end of the overhang? only 2 supports on a 20' width?
can i attach from the end of the over hang to the existing posts with a 2x6 on a downward angle? im not sure how this is called:confused1:

 

[Michael Thomas]

what the most i can make an extension on the deck using 2x8s? can i do 3 feet at least?

Max overhang is Jl/4, Max Jl for southern pine (for example) on 16" centers is 10' 6" (126"), so the max overhang is 126/4 = 31.5"

Details are here:

Prescriptive Residential Deck Construction Guide - AWA - (B)

 

[Scuba_Dave]

OK
If the tan area is the exisiting deck
The green area is the new deck
Joists will run the shortest length
You would need 3 new (black sq) posts to support the addition
This is using joist hangers to hang off the existing deck on one side & joist hangers on the other side to hang off a new board running the 20'

Is this what you are trying to do?
This is a bit of work for only an added 3' x 20' of deck :huh:

 

[Scuba_Dave]

Side view of hanging the 3' with angled support down to the existing support

I'm not sure this will work
That's a lot of weight to support at an angle
How far off the ground is the deck?

 

[boddah]

that 2nd pic is what i was thinking. it will be too much weight to support that way? and it is 6' off the ground

 

[12penny]

If a customer came to me with a request such as yours I would handle it this way. I would sister new 2x8's, 16' long to the existing joists. Make sure they rest on and are attached to both beams. With a 16 footer you should be able to get a 4' or 5' cantilever. IMO that is the easiest and therefore the cheapest solution. Good luck. :wink:

 

[Maintenance 6]

Good working rule is that a cantilever should not exceed 4 times the height of the joists. 2x8= 7.25 inches high x 4 = 29 inches.

 

[wildcat]

Side view of hanging the 3' with angled support down to the existing support

I'm not sure this will work
That's a lot of weight to support at an angle
How far off the ground is the deck?

To add an angled brace like that would require the columns be much larger, a 4x4 will not work in that situation. What is happening there is that the angled brace is inducing a moment into the column, which will reduce the column's ability to take load vertically. How much will it reduce it? It all depends on tall those columns are, the taller they are the more likely it will buckle, thus greatly reducing its capacity.

 

[Scuba_Dave]

Right, the angle support changes everything
I think if I was going to go to the trouble of adding on to a deck this size I would go out 5' & put new support posts down