Deciding on adding a half bath in cozy cottage.

[Beverly Benitez]

The property I’m in with three young kids is a 2 bed 1 bath with very limited space. I’m wondering if it would be worth the $4-5k to add a half bath (un permitted) in one of the already very small bedrooms. Bedrooms are basically 11 x 10 and each already have small closets. 
I plan to keep this home as a primary residence for at least 1-2 more years. Any advice on if this estimate is reasonable and if it makes sense financially?