huangyhg

wood decay/insect damage
does anyone know of any references that give guidelines on how to determine the length of time that lumber has been rotting or how long it has been infested by termites/carpenter ants? for insurance investigations, it is often necessary to establish an approximate time frame as to when damage first began, but i haven't been able to come up with much information. i've heard some rules of thumb (a well established colony of termites will destroy x board feet of lumber per year), but haven't seen any write-ups.
yes, you should be able to find the information requested by checking out some of the timber bridge manuals from the us forest service. in fact, nowadays they may even have the document on line.
based on my experience (yes, my own home. and yes i did have a termite inspection!) of severe termite infestation, i found that it was generally reported that termites will destroy about 2" per year of lumber. i suspect that number really depends on the size of the termite colony and as time goes on and without deterrents the colony will increase as will the damage to the residence.
don't know about termites, and i'll assume that the rot is the one commonly referred to as 'dry rot' (brown rot). to the best of my knowledge, there isn't a method. for recent brown rot, you could be in error by year(s) and for old dry rot, the error could be decades (i'll use the term brown rot for the balance).
the rate of deterioration generally depends on the extractives within the wood (these vary with the species and can vary within a species depending on whether the tree grew on the north or south side of a hill, in the same vicinity), the moisture content (climate conditiions) and the type of brown rot fungus involved.
the deterioration is dependent on the type of species, density, growing conditions, and numerous other items.
the damage is named brown rot because the particular types of fungus attack the cellulose of the wood and leave the lignin, giving the damaged material a brown colour. there are several types of fungus that do this type of damage; some are more agressive than others.
all of the fungi that i'm aware of require moisture and there is a threshold of 18% to 30% where the fungi are active. some literature indicates that the threshold starts at 22%. i think the 22% value is more correct, but when checking buildings with a moisture meter, i use 18% as a threshold (10-12% is a common moisture content and well below the threshold).
most of the fungi have the ability to 'wick' water via small 'tubes' within their structure. this permits the deterioration to occur a distance of a couple of inches from the actual water source.
the deterioration is also progressive. if sufficient moisture for brown rot to occur is present this year and not for the next 10 years, the fungi becomes dormant, only to continue when conditions are favourable.
timber can lose 20% of its strength due to rot that isn't apparent. when it becomes visible, the loss is greater (cellulose walls provide the significant tensile strength).
the encyclopedia of wood is an excellent general reference, i think the publisher is stirling, from new york (will check when i get to the office).
thanks for the information. i'm in agreement with the problem involved in setting a timetable for rot. there are too many variables. the question that often comes up from an insurance perspective is a determination as to whether damage is months old or several years old. the earliest time frame i've been able to come up with was with a house that was constructed 4 years ago, and now has significnat structural damage due to rot, in both the walls and sills. i haven't been able to find anything that would indicate, even in the worst of cases (constant moisture, a wood species that isn't naturally resistant, etc)that significant rot could occur sooner than a few years. the other issue is termites/carpenter ants. i have been told a well established colony will destroy x inches of a 2x per year, but i haven't seen it docymented in any publication. for example, if in examining a bottom plate of a 2 x 4 stud wall, you find that 5 feet of the plate is completely detroyed, can an approximate time frame be placed on how long the termites have been active?
try this site , may be useful
thanks for the info... and if you try
sfred:
the time for damage depends on the type of fungus... i will try to dig up the name of one that did significant damage in only a few months! i wasn't involved in the project, and only glanced at the file in preparation for another report.
great link, bmlcghee. this gave me exactly what i was looking for. for anyone interested, it says "based on normal feeding activity, it takes 3 to 8 years to cause appreciable damage. there have been some predictions that, under ideal conditions, a termite colony of 60,000 workers may consume a one-foot length of 2" x 4" pine in 118 to 157 days."
sfred:
correction to my earlier post...
greatest decay occurs when moisture content is above fibre saturation point (30% +/-)
and continues as long as air is present.
people,
forgive me, i know this is not exactly dealing with the subject, but next time try to use light gauge steel instead of wood framing in termite infested areas. your clients will be delighted.

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