Work has begun on a £500,000 extension to the Bridge Lane Beth Hamedrash in Golders Green.
Congregant and philanthropist Leo Noe laid the first stone at a ground-breaking ceremony on Sunday.
The new building has been 10 years in inception, due to planning issues and redesigns. As "green and ergonomic as possible", it will incorporate a day centre for the elderly.
Beth Hamedrash trustee Jonathan Wachsman said: "The new synagogue will make an enormous difference. There will be more space and functions can run side by side."
