For man [the part of body] from navel to knees is satr .i.e it must be covered.
"says that Conceal your satr, but from your wife or slave girl." Hearing this, the companions Razi Allah Anho asked what to do when one is alone in the house? Our blessed Prophet Sallalaho Alaihi Wasallam replied "Allah deserves it more than others that you be shy of Him.
Has also prohibited us to look at others satr.
Note: Nowadays, fashion has dictated semi nudity for both men and women; shorts are commonly worn at home and in public without any regard or fear from Allah (S.W.T).
May Allah Give us Hidaya and forgive us. (Aameen)