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Wood Rot

Wood Rot

Wood Rot

just throwing this out there to see what kind of responses I get....


if moisture is present (I know, it depends on the source) how long does wood rot take to occur?

looking for any discussion starters.


RE: Wood Rot

There's too many variables, how much moisture, is there decent air flow (even if it is moist air flowing), etc. Wood rot is like rust, you never know when or how much but you can be sure in the right conditions it inevitably will happen.

RE: Wood Rot

Well, and water is one of the best wood preservers out there, when fully submerged. That's why things like wood piles survive and deteriorate as the do, and why boats like the Vasa can be found so many years later (http://www.vasamuseet.se/en/)

I've also seen lumber, natural and engineered, turn to mush (literally) in the course of a few years, with consistent wetting cycles.

So give us some more details?

RE: Wood Rot

The more oxygen that is available, whether from the air or water, the greater the rate of deterioration of the wood.

That is why pile start decaying in the tidal fluctuation area. And it is also why perfectly good timber can be found at the bottom of lakes where the dissolved oxygen may be very, very low or non-existent.

In 1982, during the construction of a new building with a steel pipe pile foundation, we discovered a 24" round Douglas-Fir timber pile 4 feet below the ground line, just east of the then Kingdome location in Seattle, where the pile was still as good as the day it was installed over 100 years previously. We used the pile... It had to be a 40 or 50 ton pile.

Mike McCann
MMC Engineering

RE: Wood Rot

msquared, I'm not a pile expert..... but would mixing pile types cause problems with load sharing due to the different stiffnesses? Did you use the pile to "appease" the owner or did you really reuse the pile?

RE: Wood Rot

A 100 year old D.Fir timber pile basically has the same stiffness as a concrete pile. It is crazy I know but true.

RE: Wood Rot

We really reused the pile as it was in the middle of a pile group.

When we load tested the DF pile with a short section of the 8" steel pile we were using, the steel pipe pile failed. That was good enough for us.

Mike McCann
MMC Engineering

RE: Wood Rot

Species of wood is a huge factor.

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

RE: Wood Rot

As jayrod noted, there are lots of variables. Some of the replies above have been related to wood piles; however, the most common form of wood rot for structures is the superstructure, not the substructure.

The moisture content is perhaps the most relevant indicator of potential for wood rot. Couple that with species and you can get a good idea of when rot might occur.

The defining break point from most studies is that wood that is below 20 percent moisture takes a long time to rot and if below about 15 percent will not rot. Moisture contents above 20 percent will rot on a somewhat predictable time schedule. For softer structural wood varieties such as spruce, pine and fir, that rot will often occur within two to three years if in confined spaces such as wall cavities. Air flow changes the moisture content, so having air flow is good...but not available within wall cavities for a variety of reasons.

When the moisture content of wood is expected to be above 16 percent but below 19 percent, we have to compensate structurally for that condition by NDS.

Kiln dried lumber is typically dried to a moisture content of 19 percent or below prior to selling.

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