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StructuralEng
StructuralEng, Consultant
Category: Structural Engineering
Satisfied Customers: 6866
Experience:  Structural Engineer
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I have a client who wants to extend his deck if possible. Posts

Customer Question

I have a client who wants to extend his deck if possible. Posts are 6x6 at 6' o.c. Beams span 10' from the house to the posts. We would like the maximum cantilever beyond the posts. How far can we cantilever the 6x beams and what size 6x will permit the maximum cantilever? Floor joists will be installed on the beams per composite decking manufacturer's specs. This is central CA, so snow us not a factor.
Submitted: 10 months ago.
Category: Structural Engineering
Expert:  StructuralEng replied 10 months ago.
Hello
Expert:  StructuralEng replied 10 months ago.
I can help
Expert:  StructuralEng replied 10 months ago.
The larger the beam the further you can cantilever. How far do you want to cantilever? I can tell you what size you need.
Customer: replied 10 months ago.
We would like to extend the deck 5' beyond the 6x6 posts, if possible, which are 6' O.C. and 10' from the house, thus 1/3 of the deck would be beyond the posts. The plan is to put 6x8", 10", or 12" beams (as necessary) from the house out over the posts, and then standard floor joist framing on top of the beams per composite deck manufacturer's specs.
Expert:  StructuralEng replied 10 months ago.
So removing the existing beams and installing new beams?
Customer: replied 10 months ago.
Yes, ideally, we would like to retain only the existing the post locations due to the degree of difficulty required to change them. The entire balance of the deck is being replaced. This is why we are trying to increase square footage at this time.
Customer: replied 10 months ago.
(Posted by JustAnswer at customer's request) Hello. I would like to request the following Expert Service(s) from you: Live Phone Call. Let me know if you need more information, or send me the service offer(s) so we can proceed.
Expert:  StructuralEng replied 10 months ago.
You'll need a 6x12 doug-fir no. 2 to span 10' with a 6' cantilever if they are spaced at 6' on center.
Customer: replied 10 months ago.
So uplift is not a concern on the backspan even with as much as a 6' cantilever? And the 6x6 posts will be sufficient to bear the additional weight of the cantilever?
Expert:  StructuralEng replied 10 months ago.
The posts are ok. There could be uplift on the backspan if there is live load on the cantilever and none on the backspan. You'll need to have the connections designed to take the uplift load from the beam to the post and post to foundation and then make sure the foundation is heavy enough to hold it down.
Customer: replied 10 months ago.
The uplift will be transferred to the ledger on the house to which the beams will be connected with Simpson hangars. There should be no concern regarding uplift forces being transferred to the foundation, as there would be no chance of lifting the exterior wall off the stem. My main concern was uplift between beams and ledger, and between ledger and exterior wall to which it will be bolted. I'm wondering if standard Simpson hangars fastened with specified nails will suffice, or if I need to resort to bolting the beams to the ledger?
Can I also get a copy of the calcs you ran to include in my file on this job?
Expert:  StructuralEng replied 10 months ago.
How the ledger is connected to the house and that's to the foundation is hard for me to comment on without seeing
Expert:  StructuralEng replied 10 months ago.
I can provide detailed calculations as an additional service if you would like that
Customer: replied 10 months ago.
The exterior of the house is sided with 5/8" T1-11, and the ledger will be bolted to the 2x4 studs in that wall. What do you recommend for number, size, and spacing of fasteners? Also, will standard Simpson hangars with specified nails suffice for the beam to ledger connections or do I need to resort to some method of bolting the beams to the ledger?
Expert:  StructuralEng replied 10 months ago.
I can help with the connection to the ledger, but I need to SEE the rest to go any further
Expert:  StructuralEng replied 10 months ago.
A Simpson hanger for the 6x12 will need an uplift capacity of 350 pounds minimum to work
Customer: replied 10 months ago.
I see that a standard Simpson HU612 nailed with the specified 16d nails withstands more than 3x the 350# ***** force you mentioned, so it appears it would suffice for the beam to ledger connection? If the beam to ledger connection must be able to withstand a 350# ***** force, would it stand to reason that 350# ***** by the number of beams (in this case 3) would equal the uplift force the ledger to house connection would need to withstand?
Expert:  StructuralEng replied 10 months ago.
No. That's beam/ledger. Ledger to house is different. Also check - the hanger typically requires nailing to a double beam, not a single. Is the ledger a double or single?
Customer: replied 10 months ago.
Yes, I understand the 350# ***** force you gave me is the force applied by a single beam to the ledger at the point of connection. Will not the total uplift force applied to the ledger equal the sum of uplift forces applied by all the beams connected to it? (In this case 3 beams)
Expert:  StructuralEng replied 10 months ago.
Correct.
Customer: replied 10 months ago.
The ledger to which the beams will be attached will be 14' long. It will be secured to the 2x4 studs in the exterior wall. Using standard deck load ratings in conjunction with the calculated uplift force can you specify what size lags and how many should be used?
Customer: replied 10 months ago.
The ledger will either be a double 2x12 or a single 4x12
Expert:  StructuralEng replied 10 months ago.
Ok.
Expert:  StructuralEng replied 10 months ago.
Do you have any other questions on this topic? If you could rate my answer, I would appreciate it

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