Is it proven to be defective or it just an opinion?  You used the words "may be" that leaves the door open for a can of worms.  Are ALL the homes defective?  

Disclose, Disclose, Disclose!  Your safe if you disclose.

It will depend if you know for sure, first hand knowledge, results of a test or inspection or such. Then yes you would have to disclose for your listings or to your buyers

I would leave it alone until I was sure it is a defect.  

What John said. " may be defective" No. Only if it is proven to be defective should it be disclosed.

John McCormack said it as well I could. As a realtor who is obligated in NC to disclose material facts about homes, I'd want to know and I would disclose. You may be under different rules as an inspector.

I don't know if it's required, but I would.

Yes.

You should approach it on a case-by-case basis supported by known facts, not opinions or conjucture. You cannot afford to waste time, or money defending yourself in a civil case.

I wouldn't go there unless I had absolute facts and then I would only report it on the house you are inspecting. Your comments to others in the neighborhood would not be welcome remarks and could hurt your reputation as a home inpsector that is trying to cause a panic in the neighborhood. Let the neighbor/homeowner you are dealing with spread the word. Neighbors talk.

Michael Thornton I would disclose that there is a potential issue with the siding and recommend they bring in an expert to determine if it is defective.

Leave it to an inspector to determine if it is. Hearsay will get you in trouble.

Was all of it defective...just one "run"...?  If all the manufacturers product is defective guessing they won't be in business long...I would recommend that it be "evaluated" by whatever expert....and know what the remedy is..recall...replace

I've learned if you are asking a question such as this one than you already know the answer to it.  Think your conscience may be prompting this question and when my conscience is posing a question like this one I know I need to let those I represent know the information I have at hand.

I think you should disclose what you know in the inspections - it may be defective - here are the sources for my concern - etc. Are there any easy solutions or is it a question of taking all the materials off the house? that is something else that people need to know as part of the disclosure. 

Yes, I think you should disclose the discovery of defective materials. If I were the home buyer, I would want to know and would assume that one of your tasks is to advise me.

Licensed agents in every state are required to disclose material facts that may effect the value of the property or influence the buyers home buying decision.

This one is easy for me.  I represent the home buyer and will always disclose everything I know about the home, neighborhood, proposed roads etc...even if it is just a rumor.

Eve

Ps:  If you are a home inspector, you were hired by the buyer for your expertise...if you know something about siding defects in the neighborhood, why would you keep that a secret?