In Washington state, legally separated filing jointly, can one spouse living in the house qualify the couple for capital gains exemption when selling the home?

[KeshaH]

If only one spouse meets the "use test" (living in the home for 2 out of the last five years before the sale), you can exclude up to $250,000 of capital gain.

Only one spouse has to own the home, but both spouses have to live in the home for two years to qualify for the full $500,000 exclusion.

See Publication 523.

[Opus 17]

When filing jointly, you would claim either $250,000 if one spouse qualifies, or $500,000 if both spouses qualify.   The spouse who moves out qualifies for their $250,000 even if they did not live in the home 2 of the past 5 years  as long as part of the separation agreement allowed the other spouse to remain in the home.   This is on page 3 of publication 523, special rules for divorce and separation.