Brothers spend $4 million on Concord house to build a duplex

Records show the home last traded in 2012 for $1.89 million.

A pair of builder brothers bought a Concord knockdown for $4,024,000 at auction on Saturday so they could build a duplex and live next to each other.

The three-bedroom property at 8 Alton Avenue had DA approval for a duplex. The site…