The only time I adjust my truss rod is when switching string gauges to something with either more or less tension than what I was using. The adjustment, which is not always required depending on the change of tension for each particular string sets, restores the neck relief to my preference. I have never noticed humidity impacting my neck relief, but I sure have seen it impact string height from the top either slightly swelling or sinking... and I keep the relative humidity in the place where my guitars are between 40-55%. When I can keep the relative humidity (RH) in a slightly narrower range, my setup stays rock solid and stable on all of my guitars. I consider outdoor humidity to be "irrelevant humdity", unless of course you store your guitars there! By the way, the factory recommended way to adjust string height on an NT neck Taylor is by changing the neck angle ("neck reset") by exchanging the precisely machined shims Taylor installed in the body/neck joint at the factory for a different size -- that way you do not have to change the saddle height, which can affect tone dramatically.
Ignoring humidity for a moment, over the long run, action eventually will rise on any guitar as the sound box distorts slightly over time from string tension. If a guitar body is built lightly enough to sound good and be responsive then this WILL happen. This is why guitars need neck resets eventually (sometimes it can be decades!) and you see players shaving saddles lower and lower to maintain proper string height. Sooner or later there is very little saddle exposed and a very shallow string break angle over the saddle, which kills both tone and volume. On an NT neck Taylor, a neck reset is a quick, cheap, and easy process compared to guitars with glued neck joints.
When string height begins to go lower on its own, which can cause string buzz, that usually indicates the top drying out and sinking a bit due to low relative humidity in your case/guitar room. Of course, the top can rise from excess humidity and raise the action. These are the seasonal changes that can cycle back and forth throughout the year (depending on where you live) if your guitar is not kept in a controlled RH environment. It is crucial that when you have your guitar set up and the neck angle adjusted, you have it done when the guitar is properly humidified and kept in a stable humidity range. In other words, if you have your guitar set up when it is "wet" that perfectly set action will fall some when it is at proper humidity and then fall some more if your guitar becomes "dry" and the strings will buzz. Most makers agree that 45-50% relative humidity is ideal for acoustic guitars. Controlling the humidity in your guitar case is the easiest approach as it is a small space. Taylor has great info on humidity. Check the Taylor site or the paperwork that comes with a new Taylor from the factory.
Sure, there are lots of other ways for strings to buzz that others have mentioned like a high fret, incorrect string height at the nut, action too low, too little (or negative) neck relief, technique, incorrect neck angle, lighter string gauges without truss rod adjustment... etc. so there are many other things potentially to sort out, but if you don't keep your guitar at a proper and relatively stable RH, you'll be fighting an uphill battle... so this is the first thing to check and solve, if needed. Rest assured Taylor will take care of you if something is amiss with the build of your guitar or the work of their factory authorized techs. Taylor's Customer Service Dept. is legendary! Best of luck with getting your issue solved!!
