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Dry rot: is there a prescriptive approach to repair vs. replace?

R

Robert

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Jan 29, 2016
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345
Location
Pinole, CA
An existing apartment complex (10- 2 story buildings) has dryrot damage on exterior structural posts and beams. I am trying to find an approach that I can tie back to literature, guidelines or a code to determine if a member needs to be replaced vs. repaired ie: "if this, then this"? Something like: "if greater then 20% of the wood thickness is decayed, then replacement is necessary". In a perfect world the owner would replace, but the difference could be millions of dollars. This is in CA. I believe termite repair folks have to make similar decisions. Thanks.
 
They have hired an engineer for one of the buildings and he wanted to replace everything. Engineer is conservative and Owner can't afford total replacement. ie: replacing a beam means replacing the concrete walkway it supports, means replacing the guardrail means replacing the stairs...etc, etc...a rabbit hole. I feel there is some middle ground somewhere but need to have some reasoning behind the decisions to repair vs. replace. Some repairs would be epoxy, Some deeper repairs could be steel rods embedded and new wood spliced on. I think similar reasoning goes into fire repair...some members can be salvaged depending on the char depth. Perhaps insurance companies have rules of thumbs they use to determine what they will pay for. I was hoping to find some manufacturer literature that would layout at what point the damage is beyond the workability of their product, and that would help me make some decisions.
 
Very likely the engineer is right but it is easy to deal with bad news by labeling the engineer as conservative.

Do not believe that you will find a prescriptive solution. The need for replacement will be very much case specific..

Hope you have found the source of the water and have corrected the problem, otherwise you have no benefit from the replacement/repair work. While it is called dry rot the rot only occurs if there is a source of water.
 
Thanks Northstar I will follow up. Mark I agree, case specific, each member needs to be analyzed on its own merit, and there are standards that need to be met in order to repair the member or replace it....that is what I am after. Most damage is beam ends, post caps and post bases, all original from 50 years ago. I can repair 2' of a beam end with steel rods and epoxy, or I can replace the whole beam disrupting the floor of one apartment, and the ceiling of another apartment (the beams cantilever out from the floor framing)...loss of rent from two units at each beam, multiplied by 10 buildings, etc. American Wood Council may have some guidelines.
 
What is your code basis for using steel bars and epoxy to repair rotted ends of a wood beam? Without a code basis for such a repair an engineer that took such an approach would be liable if there were subsequent problems.

I can envision replacing the beam with minimal impact on the unit above and that would not require access to the upper unit for more than a day or two at the most.
 
Just as epoxy pull tests are done in concrete, similar testing is done with wood. It does appear to be an option. I have found some good material from the AWC called "Condition Assessment Manual" that is used by industry experts. Destructive and non-destructive assessment. At the end of the day, it will at least give the owner options that he can make an educated decision with his engineer. It is easy to just replace everything, especially with someone else's money, but I owe it to the owner to look at options.
 
Mixing wood and epoxy is more complex than you appreciate. For example when the moisture content of wood changes and epoxy does not expect problems at the interface.

Robert what is your official role with regards to this project
 
Architect. I appreciate your feedback. The decision making process will certainly address your concerns. As I'm diving deeper into this, I am seeing epoxy repair done on wood bridges, pilings and historic structures where complete replacement is difficult. Will have to look at manufacturer specs, engineer approval, and ahj approval. I am on the right track with the AWC as they are less biased then manufacturer literature.
 
Robert

I recommend that you talk directly to the owner's engineer. No good will come from you presenting the owner with reasons to doubt his or her engineer. It will be best for all if both you and the engineer can agree on a common approach.
 
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