Old Deck Inspection Issues 7

[fabbdc]

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?

 

[JAE]

I think you have to analyze the deck per current code provisions and state the facts.

If the deck has worked for 27 years, well and good.

But if the 2x8's don't work (using the correct species/grade and current required loading) then they don't work and the owner (and inspector) needs to know where the deck is relative to required strengths.

I get ticked when I'm told "hey, that structure has stood for xx years and not fallen down, why do you now say it is unsafe?" - probably because the actual loading possibly took the structure to within a small percent of failure without anyone knowing it.

Also - you shouldn't "seal" the deck. You should only seal a report/letter stating the facts you know. Sealing the deck, whatever that means, assumes you are taking full responsibility for the deck in all cases and circumstances. You should rather seal a letter stating what you know. That is all that any engineer can possibly do.

 

[Eldorado]

I have to agree with JAE on this one. Disregarding Code is a tempting path. Come to your conclusions based on the best information you have and apply it using accepted practices. I would agree with turning something down because it doesn't feel right or deferring for additonal review, but I would NOT suggest you approve something that doesn't meet code just because it does feel good.

 

[MiketheEngineer]

Agree with JAE - Point out any problems you see with current codes and let the owner/buyer decide what to do.

My guess (like most decks) have never even come close to design load. Even if they did, the Safety Factors kicked in and therefore no failure.

Don't "seal" the deck - just seal your report pointing out areas of concern. IF they want a new deck - then design it to code and seal that.

 

[woodman88]

You should understand that the lumber values and equations all changed in the 1991 NDS, from what they were before. If you are going to do any calculations on the lumber you should be using the earlier lumber values and equations. Especially if you are going to say that it does not work. If the owner goes to another engineer who uses the earlier lumber values and equations and they state that the deck works. The owner could file a complaint with your Board of Engineering about it.

Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.

 

[RFreund]

I'm not sure how complex of an analysis you want to get into but...
You could analyze the existing members based on older allowable stress values as woodman noted. Then try to assume that the deck acts like a horizontal shear wall (or cantilevered diaphragm if you will). You would then have to try and assume some type of Tension/Withdrawal resistance of the joists connected to the ledger-board and ledger to house. NDS has allowable diaphragm shear values. And/Or even consider some of the post/beam connections as "moment" connections. I think an in-depth analysis of this kind would reveal why some wood structures have not "failed" but I would not want to rely on these analysis techniques in 'certifying' or designing new.

Is this a deck or a "3-seasons room" with roof?

EIT

http://www.HowToEngineer.com

 

[concretemasonry]

The home inspector was doing his job well to point out that an engineer should review the structural aspects of deck. Since there apparently was no modification to the deck, as long as it met the standards when it was built, the original code and material standards applied. Home home inspection is NOT a code inspection, but is a visual inspect for general condition of everything from drainage to electrical, mechanical, roofing to alert the owner to potential future costs and problems.

That is a common "red flag" thrown out by a good home inspector to have the homeowner alerted. Since he only got $250-$400 for a full visual inspection, he dumps the detailed responsibility it on the real experts. Thank God that he did not try to engineer the old deck according to today's codes.

Make sure you look at the connection of a ledger (if used) to determine if it has survived the common aging problems (moisture and rot) that can reduce the structural capacity significantly. There probably may not be any soil borings to go by.

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.

 

[msquared48]

A few thoughts here:

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 extremeties 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 issus. Just make sure the ledger is not inset and actually bearing on the wall - then there would likely be no issue.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[JAE]

Regardless of age, the "old codes" under which the deck was design/constructed (assuming it was even designed to a code) do not apply.

At least in the US, the current codes must be applied to any capacity check or engineering review. Granted the older wood values for Fb, etc. should be used but
not the old code itself.

 

[woodman88]

JAE - As I read the code, per the 2009 IBC Chapter 34 Existing Structures. Section 3401.4 Building materials.

"3401.4.1 Existing materials. Materials already in use in a building in compliance with requirements or approvals in effect at the time of their erection or installation shall be permitted to remain in use unless determined by the building code official to be dangerous to life, health or safety. Where such conditions are determined to be dangerous to life, health or safety, they shall be mitigated or made safe."

Now some repairs, etc. will need to be done per the current building code. But the structure in place can be evaluated per the requirements in effect at the time of erection. Unless the Building Official deems otherwise.

Which code or section of are you looking at?

Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.

 

[JAE]

woodman88, I see that section as referring to the materials themselves, not the structural system. (Our current city uses the 2006 IBC and the section 3401.4.1 wasn't in the 2006).

The sentence reads "Materials already in use...".
So the materials can be evaluated in compliance with the code that was in effect at the time of erection(i.e. use the older wood stress values).
The loads applied to the deck, the design analysis, capacity checks, etc, in my view, must be based on current code.

The last phrase "....shall be mitigated or made safe."....safe based on what? Current code is what I would use.

3401.4 is all about materials. It appears to me that 3404 and the rest of chapter 34 keeps referring to meeting the code for "new construction" which would be the current code.

It is silent on what to do when an inspector requests a simple review of a structure's condition and capacity. Again - I'd use the current code.

One crazy example here would be checking out a steel moment frame in Los Angeles where the detailing was based on provisions of a code prior to the Northridge earthquake.
Many of those moment frames failed in that event and the newer codes better address the weld/column cracking that occurred. If we can use the older code under which it was erected then
we would be validating a dangerous condition.

I know that our engineering judgement still should kick in regardless. Like I said - a crazy example.

 

[concretemasonry]

woodman -

Keep in mind a code is only a minimum and not necessarily the thing to hang your hat on when it comes to signing off on a professional basis.

How do you even know the original materials even met the code at that time?

The politics of writing and accepting codes unfortunately are affected by the major lobbies that always make sure the voting members are in attendance when the votes are made. Usually testing is based on older materials (dimensions and testing methods) and not what is currently available if any modifications are made. Deterioration due to climatic conditions over time are very difficult to incorporate into a serious assessment of present capacity. Joints and connections are the key points and unfortunately any factual assessment requires some serious testing, so a good detailed evaluation is necessary.

Ledger connections are very critical because the huge amount of problems with collapses, lack of flashing, moisture, rot and the newer requirements for through bolts and not lag screws in many areas due to the ability of a local area make higher standards than a model code based on local history. This is one the main reasons for the increased us of free-standing decks.

Dick




Engineer and international traveler interested in construction techniques, problems and proper design.

 

[woodman88]

JAE - I would love to redesign buildings for the current Building Code. If it is in the current or any Building Code I will be happy to go point it out to the Building Official myself to get more jobs. But it is not (any where I can find) in the codes (IBC, IRC) that existing structures must meet the current Building Code. Unless the Building Official deems otherwise.

Yes, if the owner wants to change, alter, add to, and do some types repairs, then the provisions for these shall meet current code.

But, per the 2009 IBC (and it is not marked as changed from the 2006 IBC)
"102.6 Existing structures. The legal occupancy of any structure
existing on the date of adoption of this code shall be permitted
to continue without change, except as is specifically
covered in this code, the International Property Maintenance
Code or the International Fire Code, or as is deemed necessary
by the building official for the general safety and welfare of the
occupants and the public."

Now per the OP, a home inspector is asking for the structural evaluation, not the Building Official. Also fabbcd states that the deck has been "very well kept". It is only the "current code" that is the problem. Before I would go and tell a client that it does not work (per the current code) I would ask the AHJ which code to evaluate the existing structure by and get it in writing by someone in authority to give an answer.

Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.

 

[JAE]

Garth - that makes sense. I just prefer using the current code regardless.

Having said that, I don't think the different codes always significantly affect the outcomes we calculate anyway so using an older code may not help you and may even make it worse.
I'm thinking about the heavier snow loadings use back in the 1960's vs. today.

The OP insinuates that the 2x8's are vastly overstressed. I've scratched my head numerous times trying to
figure out how a previous engineer did what they did and got it to work.

My reference to using engineering judgement still stands - the older codes (some real older codes) were very vague on certain topics - bolt bearing connection capacities for one - and newer research provides me with a better estimation of capacities that another reasonable engineer would use (i.e. on the witness stand backing up my engineering services).

 

[msquared48]

And where, just where, are we going to find a reasonable engineer?

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[JAE]

You can find them - but they are expensive.

 

[woodman88]

Yes, some people will say anything for enough money.

Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.

 

[msquared48]

Yes, but that engineer is NOT reasonable!

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[chicopee]

Your report should state what you currently found during your inspection and then state that certain defiencies were noted according to the current code. Then let the town inspector make a decision to or not to upgrade the deck structure.

 

[PEinc]

I don't understand why the home owner agreed to obtain (and pay for?) an engineer's analysis of the deck. What's the next request - analyses of the roof trusses, foundations, electrical system, floor joists? What is the buyer trying to get - a newly engineered and upgraded home? The home owner could say no but risks losing the sale. It seems to me that the homeowner should be obligated to get the deck analysis only if the deck was built without a permit or the town's knowledge and the local code office now insists on a sealed design.

http://www.PeirceEngineering.com