Question:

Is a woman allowed to sit in her house with her hair exposed?

Answer:

If there are no non-mahram men, then a woman can expose her head in the house.

(Hazrat Mufti) Yusuf Ludhyanvi (May Allah have mercy on him)

Aap ke Masaail aur unka Hall Vol.8 Pg.67

A woman asked a detailed question about wearing a scarf when working at home, Mufti sahib answered in the following manner:

Answer:

The good thing is for a woman not to expose her head. However, if there are no non-mahrams at her house, then it is permissible to expose the head. It is not permissible in front of non-mahram men.

Aap ke Masaail aur unka Hall Vol.8 Pg.64

Also see here.