518 New Castle Avenue, Portsmouth, NH

Property Description

Welcome to 518 New Castle Avenue, a single-family home in Portsmouth, New Hampshire. The home offers 6 bedrooms, 9 bathrooms and 12,940 square feet of living space, listed at $35,000,000. Single-family ownership here means your own land, your own walls and room to make the property yours. The numbers worth knowing: garage parking for 5, 2001 construction and roughly $2,705 per square foot. See the listing's full details below, and reach out for a private showing of 518 New Castle Avenue.

There are properties that simply cannot be replicated. Privately sited on 7.7 waterfront acres on Portsmouth's coveted Shapleigh Island, 518 New Castle Avenue is a once-in-a-generation New England estate, an extraordinary convergence of scale, privacy, architecture, and waterfront living just moments from the heart of downtown Portsmouth. With 13,450± square feet, this magnificent Shingle Style residence was conceived on a grand scale, pairing timeless coastal architecture with exceptional craftsmanship and sophisticated modern living. Georgian-inspired millwork, stately Tuscan columns, intricate wainscoting, and beautifully proportioned interiors create a residence of remarkable presence, while walls of windows capture sweeping water views and an ever-changing maritime landscape. Across 17 rooms, the estate offers 6 bedrooms, 7 full and 2 half baths, and an impressive collection of formal and informal living spaces equally suited for everyday living and grand-scale entertaining. A newly added balcony overlooking the pool creates an elevated vantage point of the estate's sweeping water views. Beyond the home, manicured grounds descend toward the Piscataqua River, where a private deep-water dock provides direct access to Portsmouth Harbor and the open Atlantic beyond. An attached 3-car garage is complemented by a separate 2-car garage with a finished 1-bedroom, 1-bath guest accommodation above, creating a private and flexible retreat for visitors. Nearly 6,000 square feet of unfinished lower-level space offers exceptional flexibility and storage, while a new roof completed in 2025 represents a significant recent improvement. Yet perhaps the estate's greatest luxury is one that cannot be recreated: complete seclusion across 7.7 waterfront acres while remaining connected to downtown Portsmouth and its cultural, culinary, and coastal lifestyle. 518 New Castle Ave is a landmark NH estate and a rare opportunity to steward one of the region's defining legacy properties.

Location Highlights

518 New Castle Avenue is a single family residence in Portsmouth, New Hampshire, listed at $35,000,000. That works out to about $2,705 per square foot, for a home built in 2001. It has been on the market for 12 days.

At this latitude, Portsmouth averages roughly 8.4 hours of sun a day in June and 3.6 in December.

Source: zoned school names are PrimeMLS listing data; distances, sun exposure and school facts are Owl’s Nest Real Estate additions (school facts from the NCES, U.S. Department of Education) — not PrimeMLS data.

Property Details

Essentials & finishes