William H. Macy, Joan Allen and Jacob Tremblay have joined Brie Larson in the cast of family drama “Room.”

“Room,” based on Emma Donoghue’s 2010 novel, is told from the viewpoint of a 5-year-old boy — portrayed by Tremblay — being held captive with his mother in a small room. The book has sold more than two million copies worldwide.

Lenny Abrahamson has started production in Toronto and is directing from Donoghue’s script. Larson plays the mother; Sean Bridgers, Tom McCamus and Megan Park have also joined the cast.

Element Pictures’ Ed Guiney and David Gross are producing. Exec producers are Andrew Lowe for Element Pictures and Jeff Arkuss and Jesse Shapira for No Trace Camping along with Donoghue, Rose Garnett and Tessa Ross.

A24 acquired U.S. rights to the film at Cannes. Elevation Pictures is distributing the film in Canada. UTA handled the domestic sale. FilmNation Entertainment is handling international sales at AFM.