weight limit on a 2 x 10 joyce, by 21' x 12'

I understand that you may mean a 21 foot by 12 foot room. Is this correct? If you are using 2" x 10" joists on the 21 foot length on 16" centres that is not sufficient. If using them on the 12 foot length with 16" centres then that is sufficient. However, 12" centres will be far better and have less bounce if walking on a floor above. Joyce is a woman's name. Joist is a piece of wood/or other support. I am not trying to be an English teacher because I know that most people do not pronounce the "t" at the end of the word "joist". What you are hearing is jois. Comes from the old English word "giste".

It seems Joyce is really short but quite wide. Therefore, Joyce should be able to handle your weight. Give her a turn on top if you are concerned about crushing her. I recommend reverse cowgirl.