Assuming the framing underneath has not rotted or been cut up by a knuckle-dragging plumber, any house built to code in 1993 will have more than enough strength for any tub on the market. The weight of the water in in it is much more than the tub itself. I wouldn't worry at all about it.

Good news. Thanks Matt!

You are describing a pier and beam foundation. If the floor joists are at least 2 X 10 on 16" to 24" centers with a 3/4" thick sub floor you should have no problems. You should be able to check the floor joist situation without crawling around under the house. Water weighs 8 lbs per gallon so 20 gallons in a tub would weigh 160 lbs. The tub will weigh around 500 lbs.

matt, piggybacking here: do you know anything about code for *second floors* in 1978? I'm thinking I have to rule out a cast iron tub on the second floor, but if by chance we could use one, I'd much prefer to.

flyleft: same advice applies -- as long as the framing below was done to code and has not been compromised by rot or brain-dead plumbers, you should be fine. A simple test is to put a bucket of water on the floor and jump up and down around it. If you get significant movement in the water, it may need to be stiffened.

Remember that just two or three good-sized people (say 200 lb. apiece) are going to put far more load per square inch than any tub.

matt, thanks so much. Seems rather intuitive, doesn't it? Oh well, I'm thankful you were kind enough to write it out.