When architect Peter Pennoyer took on the renovation of a four-floor Italianate redbrick townhouse for clients in Greenwich Village, he had no idea he was embarking on a three-year-long project. The homeowners also enlisted interior designer Shawn Henderson to give the classic townhouse a contemporary feel. Here are five things they learned from the magnificent transformation.

Get face value.

To make the most of their home’s total rebuild, the owners fashioned an updated take on a classical townhouse behind its protected 19th-century façade, even working with the city’s Landmarks Preservation Commission to add a fifth-story setback penthouse.

Throw in some curves.

Rather than replicating the building’s conventional staircase, Pennoyer and his team installed a circular version that lends serious drama and grace.

Let the sunshine in.

Replacing the parlor floor’s small windows with more elegant French doors enhanced the natural light while remaining historically appropriate.

Find the balance.

Sculptural modern furnishings selected by Henderson and bold contemporary artwork from the homeowners’ collection integrate harmoniously with Pennoyer’s classically inflected architecture.

Play up period panache.

Paneling, cornices, and other details were inspired by 1850s pattern books, while the exterior ironwork was re-created by Pennoyer’s firm, whose research uncovered a nearby townhouse by the same builder that still had its original balcony.