Old Deck Inspection Issues

Structural Engineering general discussion Wood Design
#1

SOURCE

https://www.eng-tips.com/viewthread.cfm?qid=330033

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QUESTION

I am perplexed. I’m Inspecting a deck that a home inspector requested a structural evaluation be done by an engineer. The deck is 27 years old (two stories with 4x6 post), but has been well kept (very well kept). I see all sorts of problems related to current codes: 2x8 @ 24-inch joist with an 11 foot span, 1/2-inch (assume through) bolts at 48-inches oc on the ledger, no knee bracing …. The problem is the deck is solid and has been working fine for 27 years. No signs of distress. I know that since it is existing, it needed to meet the code at the time that it was built (which I don’t have but I doubt would have been much different; I’m pretty current on the last 15 years).

The deck is solid, plumb and true (which I was surprised by). Jumping up and down, you really feel minimal movement. I have seen much worst.

The deck is solid, but how can I state that (seal it) when I know it is out of spec. I can’t believe it is as old as it is, the thing looks great. I have problem changing up things (and costing the owner big bucks ) that evidently have worked for the life of this deck. Based on the current up keep, I would not be surprised if they got another 20 years out of this deck. I am amassed at how solid it felt and looked.

How can I say its OK?

REPLIES

Msquared48

Here are a few thoughts…

  1. With the deck at 27 years old, the lumber could be 1.625 X 7.5 domension, or even rough cut members, although I doubt it.

  2. The grade used would have to have been around 1500 psi in bending for the span and load to work.

  3. With no knee braces, the lateral could be easily handled or upgraded with 2X4 flat diagonals below the joists, with tension ties at the extremities back to the residence.

  4. Are the 4X6 posts embedded in concrete pilasters making the structural foundation a pole structure? In other words, is there continuity at the foundation?

  5. The ledger connection could definitely be an issue. Just make sure the ledger is not inset and actually bearing on the wall - then there would likely be no issue.

#2

In addition to the suggestions by Msquared48, it is also possible that the live load until now has been much less than the code specifies. That situation may or may not continue into the future, but in any event cannot be used as justification for failing to meet code requirements.

You can’t.

#3

You would have to put eyes on the entire deck structure to include the connections, probing for any rot, and verify the load carrying capacity per current code requirements by calculations.

You should never certify any structure, or portion of a structure that you cannot see or analyze as it is just too risky to do so.

1 Like
#4

Is it feasible to verify the strength by dead loading it and checking the deflection?
Possibly barrels filled with water.