Date
Details
Price
Change
Source
10/14/2026
Listed
$35,000,000
—
MLS
Disclaimer: Historical sales information is derived from public records provided by the county offices. Information is not guaranteed and should be independently verified.
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Property Description
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.
Full Property Details
Full Property Details for 518 New Castle Ave
General
- Price: $35,000,000
- Taxes: $162,922 (2025)
- Status: Active
- Type: Single Family
- Source: PrimeMLS
- MLS ID: 5114173
- Updated: 10/14/2026
- Added to Site: 1 day(s) ago
Interior
- Number of Rooms: 17
- Interior Features: Cathedral Ceiling, Gas Fireplace, Wood Fireplace, 3 or More Fireplaces, Hot Tub, Kitchen Island, Sauna
- Fireplace: Yes
Rooms
Bathrooms
- Total Bathrooms: 9
- Full Bathrooms: 7
- Half Bathrooms: 2
- Bathroom 1: Bathroom Full, Level 2
- Bathroom 2: Bathroom Full, Level 1
Bedrooms
- Total Bedrooms: 6
- Primary Bedroom: Level 2
Other Rooms
- Living Room: Level 1
- Great Room: Level 1
- Family Room: Family Room, Level 1
- Kitchen: Kitchen, Level 1
- Dining Room: Dining Room, Level 1
- Breakfast Room: Level 1
- Library: Library, Level 1
- Wine Cellar: Basement
- Sun Room/Solarium: Level 1
- Laundry: Level 2
- Other Room 1: Level 2
- Mud Room: Mudroom, Level 1
Additional Information
- Pool: Yes
- Equipment: Irrigation System, Security System, Sprinkler System
Exterior
- Exterior Features: Boat Slip/Dock, Balcony, Hot Tub, Outbuilding, Patio, In-Ground Pool
Parking
- Garage: Yes
- Garage Spaces: 5
- Parking: Auto Open, Direct Entry, Heated Garage, Driveway, Parking Spaces 1 - 10, Paved, Attached, Detached
Location
- County: Rockingham
- Driving Directions: Use GPS
Heating & Cooling
- Cooling Type: Central AC, Multi Zone
- Heating Type: Propane, Hot Air, Multi Zone, Radiant
Utilities
- Sewer: Public
Structural Information
- Construction Status: Existing
- Basement Entrance: Interior
- Basement Desc.: Interior Stairs, Partially Finished
- Roof: Architectural Shingle
- Stories/Levels: 2
- Square Feet: 13,451
- Finished Total: 13,451 Sq. Ft.
- Finished Above Grnd: 12,940 Sq. Ft.
- Finished Below Grnd: 511 Sq. Ft.
- Year Built: 2001
Lot Features
- Lot Size (Acres): 7.7
- Lot Size (Sq. Ft.): 335,412
- Frontage: Yes Road Frontage
- Frontage Feet: 700
- Driveway/Sidewalk: Circular, Paved
- Zoning: SRA
Water Features
- Water Front: Yes
- Water Access: Yes
- Water Front Type: River
- Water Front Name: Piscataqua River
- Water Front Owned: 1
Financial Considerations
- Price Per Sq. Ft.: $2,704.79
- Assessment Year: 2025
- Assessment Amount: $14,154,800
- Tax Amount: $162,922
- Tax Year: 2025
Disclosures and Reports
- Surveyed: Yes
- Lot Number: 3
- Flood plain: Yes
Listed by Compass New England, LLC, Mitch Varley
We Value Your Privacy
We Value Your Privacy
We Value Your Privacy
Listed by Compass New England, LLC, Mitch Varley
Listing agent
— 518 New Castle Ave —
Mitch Varley
Compass New England, LLC
NMLS#: 1598647Get Pre-Approved Today
Schools
Schools serving 518 New Castle Ave
School District:Portsmouth School District, Portsmouth, NH
| Name | Grades | Distance |
|---|---|---|
Little Harbour School 50 Clough Drive, Portsmouth, NH 03801 | K-5 | 0.6 mi |
Disclaimer:
School attendance boundaries provided by ATTOM Data Solutions and are for reference only. Contact the school directly to verify enrollment eligibility.
Price & Sales History for 518 New Castle Ave
Tax History
Tax History for 518 New Castle Ave
Year
Property Taxes
Change
Tax Assessment
Change
2025
$162,922
3%
$14,154,800
—
2024
$158,251
35%
$14,154,800
94%
2023
$117,434
6%
$7,280,500
—
2022
$110,664
1%
$7,280,500
—
2021
$109,426
2%
$7,280,500
—
2020
$107,023
-14%
$7,280,500
-13%
2019
$124,091
2%
$8,350,700
9%
2018
$121,496
3%
$7,670,200
—
2017
$117,968
—
$7,670,200
—
Disclaimer: Historical tax information is derived from public records provided by the county offices. Information is not guaranteed and should be independently verified.
Estimate the Cost
Estimate the Cost for 518 New Castle Ave
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518 New Castle Avenue, Portsmouth, NH 03801 (MLS# 5114173) is a Single Family property with 6 bedrooms, 7 full bathrooms and 2 partial bathrooms. 518 New Castle Avenue is currently listed for $35,000,000 and was received on October 14, 2026. Want to learn more about 518 New Castle Avenue? Do you have questions about finding other Single Family real estate for sale in Portsmouth? You can browse all Portsmouth real estate or contact a Coldwell Banker agent to request more information.