# Can't find the prescribed code for this situation



## keithmaryq (Apr 8, 2020)

I’m designing an 8’ x 20’ deck that is 24’ above grade and attached to the house with a ledger board.  There will be one deck beam opposite the ledger board that is comprised of two 2x8s.  I’m planning on four 6x6 posts that are each set on top of 3 stacked 12’ x 12’ x 1.7” concrete pavers in 3’ deep holes (frost is not an issue).  The 6x6 posts will be 11’ tall extending through the deck to accommodate railings and also support the beam for a pergola above the deck.  Questions:

1.  Would notching the 6x6 posts to accommodate the deck beam weaken them too much to provide adequate lateral / twisting support for the pergola?

2.  Is back filling the post holes with gravel acceptable as opposed to concrete?


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## TheCommish (Apr 8, 2020)

Seem very high off the ground, code and DCA 6 may not cover that height, = engineering, Glenn should chime in soon


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## e hilton (Apr 8, 2020)

So the 6x6 posts are going to be 3 + 24 + 11 = 38 ft tall?   How do you plan to join shorter ones to get that length?  Any chance you have an architect or engineer involved?


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## khsmith55 (Apr 8, 2020)

Ditto what TheCommish said! If I were you I would be scared to death, if for no other reason then the lateral loading generated by the occupants from Cyclic Loading especially with a moment arm of *24'!*
Ken


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## classicT (Apr 8, 2020)

Why not just use a face mount hanger for the beam to post connection?


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## keithmaryq (Apr 8, 2020)

My bad… The deck will be 24 inches above grade making the 6 x 6 posts a total of 11 feet tall from grade to their tops...


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## Keystone (Apr 8, 2020)

1st. Your proposal of stacking 3 - 12” sq by 1.7” depth concrete pads stacked on-top of each other is where you need to restart, this would not be code compliant. Have you figured out/calculated the load of each pier in relation to the deck surface area as well as soil at an assumed 1500PSF? Start with this. 


Next issue, notching your girders that will be used to support your railing and also the pergola is a no go.  You can not notch your deck guard posts, period.  Additionally, even if the 6” by 6” post was used and notched to solely support the deck girder, no pergola above, the notch depth would exceed the required wood to be remaining after notching is complete.


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## TheCommish (Apr 8, 2020)

Google DCA 6, below are parts of the document for decks, if your code allows by reference.

the pergola, on the other hand, is beyond the scope of the Building Code and DCA 6, especially if it is above the deck which is not sized to handle the additional loads in the prescriptive section of the codes you are back to engineering for this combination.


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## keithmaryq (Apr 8, 2020)

Keystone said:


> 1st. Your proposal of stacking 3 - 12” sq by 1.7” depth concrete pads stacked on-top of each other is where you need to restart, this would not be code compliant. Have you figured out/calculated the load of each pier in relation to the deck surface area as well as soil at an assumed 1500PSF? Start with this.
> 
> 
> Next issue, notching your girders that will be used to support your railing and also the pergola is a no go.  You can not notch your deck guard posts, period.  Additionally, even if the 6” by 6” post was used and notched to solely support the deck girder, no pergola above, the notch depth would exceed the required wood to be remaining after notching is complete.



Keystone...thank you for the input...yes I did the calculations for the deck tributary areas and pier loads, and I used 1500 PSF for the soil.  The North Carolina 2018 Residential Code allows stacking of precast footings in FIGURE AM102.1(1).  I'm not surprised by your input on notching the 6x6 posts -- didn't think that would fly.  Could I instead sister two 2x6s to the side of the posts and extend them down to the bottom of the footing, and use this as the "shelf" for the beam to sit on?


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## Keystone (Apr 8, 2020)

keithmaryq said:


> Keystone...thank you for the input...yes I did the calculations for the deck tributary areas and pier loads, and I used 1500 PSF for the soil.  The North Carolina 2018 Residential Code allows stacking of precast footings in FIGURE AM102.1(1).  I'm not surprised by your input on notching the 6x6 posts -- didn't think that would fly.  Could I instead sister two 2x6s to the side of the posts and extend them down to the bottom of the footing, and use this as the "shelf" for the beam to sit on?



Very interesting to read that NC accepts stacking, always interesting what areas throughout the country allow, and glad to read you performed the research of that and tributary load. 


This may be an inspectors personal call  on permitting the vertical scabs/cats as you described to support the girder. My opinion, this is no different then how a pole barn continuous roof header is supported. However Simpson, not promoting just offering alternative, makes a bracket that is approved for this purpose. The bracket is a “Z” shape, off top of my head not certain of its designation but it is code approved.


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## keithmaryq (Apr 9, 2020)

Keystone said:


> Very interesting to read that NC accepts stacking, always interesting what areas throughout the country allow, and glad to read you performed the research of that and tributary load.
> 
> 
> This may be an inspectors personal call  on permitting the vertical scabs/cats as you described to support the girder. My opinion, this is no different then how a pole barn continuous roof header is supported. However Simpson, not promoting just offering alternative, makes a bracket that is approved for this purpose. The bracket is a “Z” shape, off top of my head not certain of its designation but it is code approved.


Thanks again Keystone..


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## keithmaryq (Apr 9, 2020)

TheCommish said:


> Google DCA 6, below are parts of the document for decks, if your code allows by reference.
> 
> the pergola, on the other hand, is beyond the scope of the Building Code and DCA 6, especially if it is above the deck which is not sized to handle the additional loads in the prescriptive section of the codes you are back to engineering for this combination.
> View attachment 6592
> ...


TheCommish...thanks for the heads up on the DCA-6...


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## ADAguy (Apr 9, 2020)

As to use of gravel vs concrete, only if allowed in NC, not in CA. Subject to movement by quake, expansive soil, dancers, etc.


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## keithmaryq (Apr 9, 2020)

ADAguy said:


> As to use of gravel vs concrete, only if allowed in NC, not in CA. Subject to movement by quake, expansive soil, dancers, etc.


thanks...I'll check the NC code...


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## Mark K (Apr 9, 2020)

When you cannot find your condition spelled out in the IRC you use the IBC.  The deck needs to be engineered.


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## e hilton (Apr 9, 2020)

An 8x20 deck 2 ft off the ground needs to be engineered?   Sounds a bit draconian.


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## TheCommish (Apr 9, 2020)

e hilton said:


> An 8x20 deck 2 ft off the ground needs to be engineered?   Sounds a bit draconian.


the deck does does not need the engineering the combination of the deck with pergola and the proposed railing system is outside of the prescriptive codes.


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## e hilton (Apr 9, 2020)

Forgot about the pergola.


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## Keystone (Apr 9, 2020)

No need to forget about the pergola. Separate  the pergola from the deck. Have the deck supported as one structure and the pergola supported as its own structure. Basically the pergola can be designed as its own structure/skeleton frame around the the edge of the deck.


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## keithmaryq (Apr 10, 2020)

Thanks for the continued replies.

It sure seems like a smallish, 24 inch high deck that integrates a pergola with four 6x6 posts should be pretty simple to design.  I want to share the posts between the deck and the pergola for a clean appearance and what I believe should be enhanced structural integrity...but I'm not an engineer.

At this point my design has the one deck beam resting on top of two 2x6s that are scabbed onto each 6x6 post and terminate at the bottom of the footer...this eliminates any notching.

I still haven't found a good reference for how deep (no frost here) to bury the posts that will extend about 11 feet above grade to support the pergola beam...but I haven't consulted with the local county inspector yet.

Any other thoughts on this are appreciated...


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## ADAguy (Apr 10, 2020)

Check "Fine Home Building magazine" if you are intent on DIY, many details shown


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