Startup Knotel Inc. is planning to more than triple its office space in New York by the end of the year in an effort to approach the omnipresence of WeWork Cos., the city's dominant name in shared workspaces.

The expansion comes amid growing demand for Knotel's niche in the shared-office market: companies with 50 to 200 employees — too big for the typical co-working environment — that want their own turnkey offices and aren't ready to commit to the kind of fixed-term leases landlords typically demand.

"We serve bigger companies than co-working does," said Amol Sarva, Knotel's cofounder and chief executive officer. "Companies prefer to use a service like ours than to sign leases, and, on the other side, ownership is finding it uneconomical to serve short-term company leases. Owners are facing customers these days who don't want to sign five — or even three-year leases."