Hold your horses there Moneypit. It wouldn't be the first time that someone tried to get past a code violation by creatively labeling a room or space as something other than what it actually will be used for. Inspectors are naturally suspicious. To an Inspector, if it walks like a duck, and talks like a duck, it is probably a duck. Despite your intent, if the room could reasonably be viewed as occupiable space, that is what the room construction has to adhere to. You could change your mind as to use, or the next owner could use the room differently, etc. That's not unreasonable. You said it yourself above.
Every Inspector is different, come from different backgrounds, and naturally sees different things when they inspect a project. Despite your inconvenience, lets cut the guy some slack. If you are in violation of code, don't blame the inspector. It's your responsibility to comply with all applicable building codes.
Your rated door should be researched a bit. The rating of the door is in relation to the rating of the wall. A 1 Hr. rated partition will usually have a 20 minute door rating. If you look at the inside (hinge) edge of the door you should see a label stating the UL rating of the door. It need not be a metal door, though it will take a solid core wood door to qualify.
You also can get into trouble by creating too large a storage area. Based on the actual size, you could be liable for smoke/fire dampers or even sprinklers. Generally this will only apply to commercial projects, but the final word, as always, is subject to local interpretation - how they view your use of the space.
No doubt there are more than a few jerks out there, but I am a firm supporter of building codes, and there is no other way to ensure compliance than to inspect at various stages of completion. Codes are compiled by experts in the field and are arrived at by consensus after a lengthy period of comment and modifications. That doesn't make them perfect, and often there are code revisions and modifications made, even prior to the next scheduled code publication.
Even though some item may not have been flagged by Plan Review prior to start of construction, the Inspector has the final word. Your best bet is to confirm that this is the sole issue, make the modification and request that the same Inspector revisit the site to confirm compliance. Save the old door for another project in the future.
As always, offered only as opinion
