Arundel Park House, including garden walls and terrace

Arundel Park House is a rendered brick house painted pale pink, with hipped roofs of graded slate featuring overhanging eaves. The eaves of the central block are decorated with paired modillions. The house follows a Palladian tripartite plan, comprising a central two-storey block with two smaller two-storey flanking pavilions connected by single-storey links. The wings project obliquely, canting inwards towards the north (entrance) front, which is positioned on an axis with Hiorne's Tower, a Gothic folly of 1787 (listed Grade II*). The south (garden) front of the central block has semicircular bowed ends to east and west, with principal rooms arranged to maximise light and views across the gardens towards the sea. The original wooden casement windows have been replaced while replicating the original design and reusing the original brass fittings. External doors are painted timber, and chimneys are rendered brick.

The north façade of the central block presents five bays, with a central semicircular colonnaded porch and a bow set back behind a metal balustrade above. Pairs of flanking windows retain partially surviving louvred wooden shutters on the ground floor. The front door is said to date from 1750, brought from Norfolk House, St James's Square, London, which was demolished in 1938. The three-bay south façade features tripartite 'Wyatt' windows set in recessed segmental arches at ground-floor level, with louvred wooden shutters to the first floor. Similar tripartite windows appear in the two-storey end bows. The north-facing link blocks have oval oculi, while the west link incorporates a glazed loggia on the south side; the east link is screened by planting. The pavilions present three-bay elevations to both north and south.

The main block is entered at the centre of the north front into a small entrance hall, with a gun room to the right. To the left is an additional lobby containing a larder, an inserted lift (formerly a water closet), and a secondary stair. The main double-height stair hall lies ahead. The kitchen is positioned to the left and the library to the right. Along the south front, with bowed ends to east and west, the large drawing room and dining room occupy the principal spaces. On the first floor, rooms are arranged around the central stairwell, with two principal bedrooms on the south front separated by a dressing room. Further bedrooms, bathrooms, a linen room, and a small study (originally a bathroom) fill the remaining space. A small spiral stair leads to a glazed octagonal cupola with a balustraded admiral's walk on the roof. The basement contains storage and plant facilities.

The flanking pavilions function as self-contained annexes, each with independent external access at the centre of its north front. Both are laid out with a kitchen, sitting room, bedrooms, and bathroom. The west link to the main block is divided into a narrow corridor on the north side and a loggia on the south. The east link contains a scullery, stores, and an extended breakfast room adjoining the kitchen.

The interiors of the main house display restrained grandeur, influenced by Soane's style, featuring simple plaster vaults and recessed arches. The vaulted entrance lobby opens to the impressive full-height staircase hall with a top-lit Soaneian vault. The staircase is L-plan with stone treads and an elaborate wrought-iron balustrade bearing the monogram of the Duke and Duchess of Norfolk, with a crystal ball finial to the bottom newel. Walls are painted render or papered, floors are Portland flags with black squares at intersections or timber with carpets in reception rooms, and ceilings are white painted render.

Pairs of double doors into and between principal rooms are mahogany, inspired by those in the Cube Rooms at Wilton House, Wiltshire. They feature gilt roundels, acanthus carving, and ormolu (a gold-coloured alloy of copper, zinc, and tin) door handles, surrounded by substantial Vitruvian scroll architraves. Other internal doors on the ground floor are of the same style but painted, with more modest moulded architraves. The drawing room and library contain fine 18th-century marble chimney pieces.

The drawing and dining rooms have dado rails and plain coved cornices. The dining room retains its original Colefax and Fowler green-printed wallpaper above the dado, with two tall niches flanking the double doors, each with an oval recess above. The library features segmental arched recesses fitted with bookshelves, and a dummy door to the drawing room is decorated with books whose titles commemorate the building of the house. The kitchen has been refitted, and the pantry, which once separated the kitchen from the dining room, has been incorporated into the kitchen. The loggia walls were originally painted with murals depicting the seasons at Arundel by Lawrence Toynbee; these are no longer visible. Bedrooms are accessed from the continuous landing through segmental-headed openings set in larger recessed arches.

The interiors of the pavilions are relatively little-altered but of much lesser architectural interest.

Garden walls are integral to the house's design. To the north, low curved retaining walls enclose the drive, with steps up to the grounds beyond. These walls are rendered to match the house's finish and have stone copings with urns flanking the entrance to the drive and steps. To the east, higher walls enclose the gardens around the east pavilion. The south terrace in front of the central block features a pair of carved stone lions on pedestals with steps down to east and west. A contemporary garage stands to the east of the house but has been excluded from the listing.