# Another deck beam span question



## Bugman1400 (Mar 11, 2011)

The deck I am planning to build is a little different than most. First of all, my deck will be 20' x 20' attached to the 2nd story of my house. The deck will also be covered using a shed style roof off the house. I also plan to have a 2' cantilever and the posts for the shed roof will rest on the rim joist at the end of the cantilever portion. So, the joists, which are 20 foot 2 by's, will rest on the beam at the 18 foot mark. 

Questions:
1.) What size joists? 2"x10"x20' or 2"x12"x20'
2.) use 16" OC or 12" OC?
3.) What size beam? (2)-2"x10", (2)-2"x12", (3)-2"x10", or (3)-2"x12"
4.) What 6"x6" post spacing should I use? 6', 8', or 10'

Mucho thanks!


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## Daniel Holzman (Mar 10, 2009)

Your deck design is off the standard deck design manual for a couple of reasons. First, it is rather tall, and the posts are likely to be taller than the standard maximum height in the IRC design guidelines. Second, you have a roof, which will add load to the structure not accounted for in the standard design guidelines. You are attaching to the second floor, which may change standard framing practice, but without a plan I can't say.

The cantilever sounds like it is within normal design guidelines, but combined with the roof, is probably not covered by your standard design guide. As for resting posts on the rim joist, that is definitely not standard practice per IRC.

In short, while you may be able to do all of this, you probably should hire an architect or structural engineer to check all the structural element sizes and connection details, especially if you are planning to pull a permit (mandatory in most jurisdictions) for this project. Without a detailed structural investigation, it would be reckless for anyone on this forum to size structural members for you.


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## Bugman1400 (Mar 11, 2011)

Daniel Holzman said:


> Your deck design is off the standard deck design manual for a couple of reasons. First, it is rather tall, and the posts are likely to be taller than the standard maximum height in the IRC design guidelines. Second, you have a roof, which will add load to the structure not accounted for in the standard design guidelines. You are attaching to the second floor, which may change standard framing practice, but without a plan I can't say.
> 
> The cantilever sounds like it is within normal design guidelines, but combined with the roof, is probably not covered by your standard design guide. As for resting posts on the rim joist, that is definitely not standard practice per IRC.
> 
> In short, while you may be able to do all of this, you probably should hire an architect or structural engineer to check all the structural element sizes and connection details, especially if you are planning to pull a permit (mandatory in most jurisdictions) for this project. Without a detailed structural investigation, it would be reckless for anyone on this forum to size structural members for you.


Luckily, my posts are not taller than the 14' maximum listed in the IRC Deck guide on page 7. For the ledger, I may have misled about the second story. My house has a walkout basement. So, the ledger will, in fact, be attached to the house band joist. For the posts that will support the shed roof, I plan to use 6"x6" post located on the outer edge of the deck. This will place them on the cantilevered portion of the deck. I guess I could just a easily place the posts directly over the beam portion of the deck.


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## Bugman1400 (Mar 11, 2011)

Anybody know the answers?


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## tpolk (Nov 7, 2009)

you need to take this to someone who can design loads and shear. I dont think you will find 18' clear span exterior material for the loads you need


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## 12penny (Nov 21, 2008)

...all the span tables are here. When in doubt, seek the advise of a structural engineer.

http://www.awc.org/publications/DCA/DCA6/DCA6-09.pdf


and no you cant put roof posts on the cantilever.


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## handy andy (Feb 25, 2011)

*What about foundation?*

I do not have the IRC deck guide, but the following points popped up in my mind when I read your post! I do not have answers other than "*have a structural engineer review your plans before you buy any materials*"!

1. 18 feet feels like a VERY long span. I think you may need engineered beams for a span this long! Of course, loading, especially with the roof adds to your problem. The extra load on your house wall could also be a factor!

2. You will need some kind of foundation for your support posts. Exactly what you need to do here will depend on soil conditions in your area. I am guessing at minimum 3' square footings on really solid soil. Your local building code will dictate. Again this is another 'engineering' item.


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## Bugman1400 (Mar 11, 2011)

tpolk said:


> you need to take this to someone who can design loads and shear. I dont think you will find 18' clear span exterior material for the loads you need


That is wrong....check the joist span tables.


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## Bugman1400 (Mar 11, 2011)

12penny said:


> ...all the span tables are here. When in doubt, seek the advise of a structural engineer.
> 
> http://www.awc.org/publications/DCA/DCA6/DCA6-09.pdf
> 
> ...


That is wrong also.....specify your source. You can put load bearing walls on a cantilever, which is what the roof posts are doing....bearing the load of the roof. However, for typical construction I thought it was no more than 1' cantilever. I figured since I was just supporting a light roof that perhaps I could go greater than the 1'.


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## Bugman1400 (Mar 11, 2011)

handy andy said:


> I do not have the IRC deck guide, but the following points popped up in my mind when I read your post! I do not have answers other than "*have a structural engineer review your plans before you buy any materials*"!
> 
> 1. 18 feet feels like a VERY long span. I think you may need engineered beams for a span this long! Of course, loading, especially with the roof adds to your problem. The extra load on your house wall could also be a factor!
> 
> 2. You will need some kind of foundation for your support posts. Exactly what you need to do here will depend on soil conditions in your area. I am guessing at minimum 3' square footings on really solid soil. Your local building code will dictate. Again this is another 'engineering' item.


1.) I don't think they make engineered beams that are ACQ treated.....this is an outside deck. I agree that the roof adds to my problem. It would really be easier if I could just use the IRC guide.
2.) IRC Guide list 32" sq footings for an 18' joist. Four more inches never hurt anybody......at least, that is what my wife tells me.:laughing:


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## 12penny (Nov 21, 2008)

...why dont you just put your posts over the deck beam? No engineering, code enforcement will be happy and with the overhang the roof edge will line up with the edge of the deck.

Something like this.


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## tpolk (Nov 7, 2009)

sounds like you have it already figured out to do the way you want so why the question bug?


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## kcremodeling (Mar 3, 2010)

The ICC residential code book is a great resource to find answers to questions like the one above.


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## Bugman1400 (Mar 11, 2011)

kcremodeling said:


> The ICC residential code book is a great resource to find answers to questions like the one above.


I have not heard of the ICC; only the IRC. I will check it out. THANKS!


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## Bugman1400 (Mar 11, 2011)

12penny said:


> ...why dont you just put your posts over the deck beam? No engineering, code enforcement will be happy and with the overhang the roof edge will line up with the edge of the deck.
> 
> Something like this.


A picture is worth a 1000 words. That really helps me out!!!!!

THANKS!

The deck portion will be almost identical to what I have planned for the cantilever. However, what would be the harm in placing the roof support posts toward the rim joist to give more area under cover? Just curious.

Also, one more important question....what is your roof slope and what roofing material are you using....certainly not shingles?


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## 12penny (Nov 21, 2008)

...you proably can move them out, what I'm saying is you will most likely need an engineer to sign off on it.

Roof pitch 2 1/2:12 and covered with steel standing seam.


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## Bugman1400 (Mar 11, 2011)

Does anybody see anything wrong with this table? Using SYP 2x12s @ 16 O.C., I can span 18 feet....with or without overhang? Is this comparable to what others show?

Thanks!


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## havalife (Mar 23, 2011)

If you are asking these types of questions on the internet and people keep telling you to get an engineer, I am surprised you have not been to one yet. Also did the IRC say it was a 32" footing for your soil type and your load for the footing? I would say get and engineer.


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## Bugman1400 (Mar 11, 2011)

I am an engineer, but of the electrical type.......state licensed and everything. However, I have asked several of my civil and mechanical engineer friends, but they know less about this than I do.........I know, I know.. I was surprised too. So, quit telling me to find an engineer. I'd rather talk to someone who has built more than one deck with a covered roof and I'd listen more to him than a moron engineer!:laughing:


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## havalife (Mar 23, 2011)

Bugman1400 said:


> I am an engineer, but of the electrical type.......state licensed and everything. However, I have asked several of my *civil and mechanical engineer friends*, but they know less about this than I do.........I know, I know.. I was surprised too. So, quit telling me to find an engineer. I'd rather talk to someone who has built more than one deck with a covered roof and I'd listen more to him than a moron engineer!:laughing:


So you are figuring out what type of engineer you need to consult?? Here is a hint "STRUCTURAL" Big difference


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## Gary in WA (Mar 11, 2009)

Big difference between a bearing wall and a point load on a cantilever.......

Gary


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## Bugman1400 (Mar 11, 2011)

havalife said:


> So you are figuring out what type of engineer you need to consult?? Here is a hint "STRUCTURAL" Big difference


I haven't seen too many schools that have a Structural Engineering degree. What would that be...... a BSSE? I think most Structural Engineers have a BSCE (BS in Civil Engineering). As I said before, one of my engineer friends is a Structural Engineer (BSCE), but does not work with wood...only steel (as in 7 story buildings).


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## Bugman1400 (Mar 11, 2011)

GBR in WA said:


> Big difference between a bearing wall and a point load on a cantilever.......
> 
> Gary


I'm guessing by your post number that you may have more experience. So, what is the load on a 2' cantilever that is 20' long with 6"x6" roof posts supporting a 1/12 pitch roof w/o a ceiling using metal roofing?

Do you remember the formulas?
T = F * d, where T = Torque F = Force (here, the force applied perpendicular to the axis)
d = Distance​


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## House Engineer (Feb 23, 2012)

Remember your lateral bracing to prevent sidesway.


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## tpteam6 (Feb 28, 2012)

sounds like you have it already figured out to do the way you want so why the question bug?



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## Daniel Holzman (Mar 10, 2009)

Your project, as I stated a long time ago, is outside the space covered by the IRC deck guide. This is because you have loads NOT CONTEMPLATED in the Prescriptive Deck Guide. This does not mean you can't build it, and it does not necessarily mean you have to hire an engineer to design it, but someone needs to design it, unless you plan to size the structural elements by revealed truth from God. And since you think engineers are morons, and you claim to know more than your structural engineer buddy, perhaps you should size the pieces yourself, figure out how to put them together, draw up the plans, take them to the building inspector, and get them approved. Or just build it with no plans and no permit, why not?

As for getting someone on here to design the job for you gratis, would you also like someone on here to show up at your house and build it too? No charge?


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