While they renovate the Gold Coast mansion (pictured at right)  they bought last year for $14.5 million, J. B. and M. K. Pritzker are living in a 13-room townhouse two blocks away. The monthly rent: $30,000.

Jay Robert ‘J. B.’ Pritzker, a member of the fourth Chicago generation of the uber-wealthy clan, is a partner in both the Pritzker Group and New World Ventures, a technology venture capital firm. His wife, M. K., has been involved with plans to create an Olympic equestrian facility in Lake County’s Lakewood Forest Preserve, near the pair’s Evergreen Farm in southern Wisconsin.

In May 2006, the couple paid $14.5 million for the 26-room Gold Coast mansion. Built in 1897, the house occupies three lots and has 14 fireplaces and a five-room guesthouse. Last year, the house topped Chicago’s annual list of the priciest house sales in the six-county metro region.

Although the Pritzkers bought the house after it had undergone a full-scale restoration, they have begun work of their own. The house they are renting in the meantime had also been recently renovated, and had been on the market since April 2006 for $6.495 million. The owners-the siblings Phil, Brian, and Pam Farley-had a different Gold Coast property up for rent, but instead they ended up renting the renovated townhouse to the Pritzkers a few months ago, a source told Deal Estate. The Pritzkers took a 20-month lease at $600,000, or $30,000 a month. Brian Farley could not be reached for comment, and J. B. Pritzker declined to comment for this story.

Built in 1891, the house has a rusticated stone façade. According to marketing materials from when the house was on sale, it has 13 rooms and a five-car garage. The master suite fills most of the second floor (it has its own library), and above it are three children’s bedrooms and a rec room. There are separate guest and nanny suites, as well as a glass-walled, climate-controlled wine room.