I have a Wood Destroying Fungus question

[Ron247]

I need some input from the wood gurus on Wood Destroying Fungus.

If I have crawl space conditions favorable to WDF and due to that, my wood joists lose some of their strength from WDF. Let's say they lost 30% of their strength before we made corrections to the crawl space.
Let's also say my moisture readings of my wood were 24% at that time. Later, I correct my crawl space conditions so the moisture in the air is reduced. By my thinking, the moisture level of the wood would also reduce, but this reduction does not correct the damage that has already occurred.

I am asking this because I see a conclusion I do not agree with in a report that states because the current moisture readings are 16%, there is no structural damage to the wood floor joists. To me, I probe the wood to determine damage and the moisture reading only tells me if the current conditions are favorable for WDF growth.

Thoughts?

 

[JAE]

I don't know much about this but the links below appear to be brief primers on the subject.

It depends on if the fungus has worked its way into the section of the lumber (vs. just on the surface).
If it has damaged the wood into its section, simply drying it out won't change the diminished nature of the member.

https://www.usinspect.com/guides/wood-fungus/

https://support.sbcindustry.com/images/publication_images/ttbmold.pdf

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[EngineeringEric]

I would say the the E portion of the stiffness of the wood has mostly returned with the correction of the moisture content... but locked in deflection may be locked in now.
The I_portion of the stiffness may be reduced if material was lost due to decay.
I assume F'b is the same after correction but that may even be reduced due to the depth of damage.

If fungus growth was so minor that it is surface only then i would say that damage never really happened and the potential for significant structural loss was reduced/eliminated.

 

[oldestguy]

I'd call or write the US Forest Products Lab in Madison, WI. Also check their WEB site. They are the experts.

 

[MotorCity]

I agree with your assessment. Just because the moisture content has been reduced, that does not magically restore any damage that has already occurred. It MAY prevent future damage.

I am not an expert on what percent of moisture is conducive to WDF, but I would expect that it could occur at 16% depending on the biological needs of the fungus. Moisture content and fungus growth
are two separate issues that are not necessarily related....you could have a high moisture content and no fungus growth. If that were the case, I would expect the only structural side effects to be
is taking a reduction in strength based on excessive moisture.

 

[NorthCivil]

If wood is moist and is rotting, drying of the timber will halt the decay (except for dry rot), though will not magically return strength to timber fibres that have been destroyed by the rot.

its very hard to quantify the level of destruction that rot has affected a structural member. There is no magic formula to deliver a %. Any attempt to do so is part experience, part assumption, and a heavy dose of mysticism.

 

[JAE]

And a follow-on comment to NorthCivil's comment....the only sure thing is to perform a load test on the floor.
This would allow you to measure specific deflections for specific loading and then back-calculate a stiffness.
It also verifies code-required loading (2 times the loading for the test or as required by the code - See IBC sections on load tests).


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[epoxybot]

This is an interesting blog entry on wood decay & assessment. Link

 

[Ron247]

Thanks all for the feedback. If they decide to enlist my services, I will definitely probe the actual wood material and try to estimate damage.

The concern I had was based on a document the Owner of the house produced that was an internet article by another engineer about WDF. The statement about them going to a project that had WDF already reported and taking moisture readings of 16% or less meant the was no structural damage is what my main comment back to my potential client was. I did not see that as being conclusive there was no damage since the damage is not necessarily reversible just because you lower the moisture content. Any strength loss due to the normal deduct we take for excessive moisture (19%) could be removed by drying but not actual physical damage.

Thanks again.

 

[Ron]

There are several moisture points of concern in wood. The equilibrium moisture content of wood in normal conditions is usually about 10 to 12 percent. When the moisture content reaches and stays at or above 16 percent, the NDS requires a strength lowering factor to be applied to structural capacity. When wood exceeds 19 percent moisture, it may start to deteriorate over the long term. When the moisture content reaches about 30 percent, you have probably achieved fiber saturation and deterioration is pretty much a guarantee!

 

[Toby43]

Agree, that load testing would provide a system performance. On a member level, a method to assess condition is to drill into the member(s) and if the cuttings from the drill bit are crumbly, then dry rot is close to setting in.

 

[Ron247]

Thanks for the tip Toby.