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.
snipped-for-privacy@home.com wrote in news:b8fbe895bc7bb68d5b7bvgm2hkhpbltboq@
4ax.com:
Upon reading this article, it appears to me that the problem only becomes a significant one if solar panels are to be mounted to the roof.
Are you really that dopey?
Well if you have a problem, get up there and give a dose of WD40 once a year or so.
That's why I said "hot dipped" All hot dipped parts are dipped after fabrication.
None of the ones I've seen are like that
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 iron rusts.
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 is solved.
Putting solar panels on top of the agricultural building has nothing to do with the problems being discussed in the PDF.
Perhaps, but that WOULD be the best for Ag building use.
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