While searching the web for truss related things, I found this article
(PDF). I was not aware of this problem, but it makes sense. These
trusses are used in most large barns these days. What is happening is
the moisture from animals, and ammonia from the manure is building up on
the truss plate connectors and causing them to corrode. This could
cause the building to collapse. I thought I'd share the article.
Well, I graduated from the U of Manitoba with a degree in mechanical
engineering specializing in metalurgy (which includes the study of
corrosion of metals ((usually steel)),) and I agree with the idea of
spraying either WD-40 or any spray paint onto the truss plates to
prevent them from rusting. Any paint or oil film will form a physical
barrier between the iron and the humidity in the surrounding air,
thereby preventing them from coming together with the result that the
Someone said that it's not a good idea to treat bare wood with an oil
(???) Linseed or Tung oils on the surface of the wood WILL prevent that
would from absorbing humidity from the surrounding air. Neither is
intended to treat the wood to kill any wood rot fungus that attempts to
grow in that wood as an end cut preservative or other wood treatment
would, but keeping the wood moisture content low WILL prevent the wood
from rotting. And a coating of Linseed or Tung oil will prevent
moisture absorbtion into the wood from the surrounding air.
But, to be honest, that study is kinda stupid. It says that high
humidity levels inside agricultural buildings can cause the wood
moisture content to become so high that the wood moisture content gets
up to 30 percent and the wood starts to rot. People should turn their
attention to Figure 4 in that PDF file that shows vents on the ridge of
that agricultural building. The purpose of those vents is to allow warm
moist air inside the building to escape to the outdoors, thereby keeping
the humidity inside the building low. Or, at least, lower than what
would be required for the wood inside the building to start rotting.
ANY kind of a coating that forms a physical barrier between the exposed
steel of the truss plates and the surrounding humid air will protect
those truss plates from rusting. And, WD-40 will last a long time
indoors since there's no rain falling on those trusses to wash it off.
Also, the reason why trusses AREN'T made of pressure treated wood is
that it's assumed that they'll be covered by a roof which will keep the
rain off the trusses, and prevent the exposed wood from absorbing lots
of moisture at it's end grain every time it rains.
That is, in a nutshell, the people making trusses are making them
properly from untreated wood, but it would be good practice for them to
coat their truss plates with an oil based spray paint (or even WD-40) to
protect those truss plates from corrosion in agricultural buildings. If
the truss manufacturers aren't doing that on trusses they make for
agricultural buildings, then the farmers or contractors that erect those
buildings should be doing it. A few cans of spray paint and the problem
Putting solar panels on top of the agricultural building has nothing to
do with the problems being discussed in the PDF.
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