I saw a commercial for an upcoming HGTV show in which a man finds a hidden room in his parents’ 150-yr-old house. My question is this: If you wanted to put a hidden room in a new house, could you do it without having it on the blueprints? Assume that the room is to be used either as a safe haven against storms or home invasion (like in Panic Room) or as a vault to hold valuables.
You could always destroy the blueprints after the construction.
Or, as Cecil pointed out in the case of Dr. Henry Holmes, you could simply keep different builders doing different things so that none of 'em knew exactly what they built:
http://www.straightdope.com/classics/a2_455.html
I always associate hidden rooms with the Underground Railroad.
Kinda like the Stealth Bomber…my uncle helped build it, and he had absolutely no idea what he was doing… 
Anyway, I would think that you would need to have confidence in the architect and the builders, and let most of them in on the secret, should you want the job done moderately well and secret…
Of course, if you’re building a house right on the street, someone’s bound to notice there is an extra 6 x 6 room.
Another thing, unless you’re in a large mansion house, you will most likely notice that there is a few feet of ‘room’ missing…
Just build the house, then throw up a few walls to make the hidden room. Adding walls shouldn’t be a big problem. It’s when you remove walls that you run into structural problems.
My wife and I have one in our home. We bought an old Victorian that was on the edge of being condemned and pretty much gutted it (It had wiring and plumbing dating from 1923 and insulation from before that). Because it had so many different nooks and crannies (and plumbing only on the ground floor) we combined a couple of rooms, converted some others and had a couple of large closets/small rooms that were sort of left over.
We made one of these into something of a passage way/closet from one bedroom to another with a sliding wall at the back of adjoining closets and the other into what we call our “priest’s hole”, basically a small secret room. Its entrance is hidden by a large quilt hanging over the wall in which the door to the hidden room is set.
As of right now we’ve not used either for anything mysterious, but if there ever were a chance we might. The overall work on the house was done by a contractor, but we did the finishing work and we are the only people that know about the passaageway and hidden room. I think.
Until now.
Bwa-ha-ha-ha-ha-ha-ha-ha!
Sorry, had to do it.
One of Jim Tolpin’s books has a small section on secret doors for rooms like this. Think “Batman (Bookcase that conceals a door)”, to get the idea. I’m searching Amazon right now, but I can’t find the exact title.
For those interested in more the title is something like “Building Traditional Cabinets”.*
I once built a paneled wall (wainscote) with a secretly hinged panel for access to gas and electrical utilities which were in the existing wall. It was too difficult to remove them, and an access door was a simpler solution. Behind the door was a small compartment in which valuables could be stored, but not much more. The door is virtually invisible.
I don’t see why you couldn’t have a room behind such a panel, but as others have said, the house must be big enough so that the missing space isn’t noticed.
It’s also true, as has been noted, that removing a structural wall invites trouble, while throwing up a partition wall is possible under almost any circumstances.
*I suspect that it may be this book
When I asked my parents if I could put a secret room in our house I was firmly told it would be against building codes. They pointed out that all rooms have to have ventilation, be escapable in a fire, etc. And that there was no way that sort of thing could meet code.
Funny thing was, we had a secret staircase in that house. It was about 1 foot wide. How it happened was that new stairs were put in, and the old ones only partly taken out when the living room was expanded. Of course this may not have been up to code, it had probably been done in the 1940s.
A guy in the Society for Creative Anachronisms near me put a secret passage from the middle of his living room to a small castle some distance away. I doubt very much he got permission to do so, since one of his other modifications was to place a high pressure water nozzle in the street outside his place. The passage was put in after the house was built.
My parents and I lived in a large house in the Hancock Park section of Los Angeles. While some renovations were taking place, workmen knocked down a wall in (IIRC) a bathroom. They found a hidden room, and in that room were several bottles of bootleg liquor that were dated to sometime in the late 1920’s, from the newspapers the bottles were wrapped in. We got our picture in the neighborhood paper, and my parents still have a few bottles. Seems the owner of the house was pro-Prohibition, and his old man was busy making moonshine.
It turns out that this house had several “hidden” rooms and passageways, although I don’t know what purpose they served. I believe the house itself dated from the early 20s or so.
I miss that house.
Robin