Olympia National and Olympia Central, Olympia Exhibition Centre

Olympia National and Olympia Central form part of the Olympia Exhibition Centre. Olympia National (the former National Hall) is an annexe of 1923 designed by architects Holman and Goodham. Olympia Central (built as the Empire Hall) dates to 1929 and was designed by architect Joseph Emberton, with alterations made in the later twentieth century. These buildings are part of a larger complex that includes the Grand Hall (the former National Agricultural Hall) and Pillar Hall (the former Minor Hall), both completed in 1885 in Italianate style by architect Henry Edward Coe with James Edmeston and engineers Arthur T Walmisley M.Inst.C.E. and Max Am Ende M.Inst.C.E., which are listed separately.

Olympia National is constructed of red brick with stone dressings and features an iron, glazed roof. Olympia Central, completed in 1929, is built of steel and brick with concrete floors. Its front range has a reconstructed stone facade made from concrete with a Portland stone aggregate, and its original glazed roof has been renewed.

The evolved exhibition centre is served by an open yard to the west with access from Blythe Road. The various halls share ground and first floor levels in places and are linked internally, though they can operate independently with their separate entrances. Internal vehicular routes known as Hospital Avenue and Portcullis Avenue run through the footprint of Olympia Central and National. The Grand Hall and Pillar Hall, aligned east-west, lie to the north. Olympia National occupies the south-east corner of the site, with its principal façade and entrances onto Hammersmith Road and a prominent corner entrance at the junction with Olympia Way. A glazed exhibition hall lies to the rear. Olympia Central is attached to the west of Olympia National, with its main entrance on Hammersmith Road. Its plan is broadly rectangular, with grouped fire escape stairs in each of the four corners, lifts to the front and steel beams of the building frame at 15-metre intervals on a square grid. The front range originally had a large light well and staircase forming a grand route through the building, which have now been lost.

Olympia National's exterior continues the façade south along Olympia Way and Hammersmith Road in a pared-down neo-classical style. The front range comprises two storeys with a glazed exhibition hall to the rear. It features a prominent corner entrance pavilion at the south-east, a central entrance block of eight bays (doors not original) and an end pavilion in Portland stone ashlar with carved details including ionic pilasters, wreaths and dentils. The façades between the pavilions are in red brick, each with metal windows with stone surrounds on the ground and first floors loosely grouped in threes, and a brick parapet above.

The interior of Olympia National has a more stripped-down aesthetic. The principal function rooms are a restaurant now in the south-east corner of the ground floor and the Apex room above. The entrance vestibule from the corner entrance on Hammersmith Road is richly detailed with mahogany panelling, mirrors and elaborate white plasterwork, a decorative theme that extends throughout the entertaining and function room suites in this wing. On the ground floor is the former function room with panelling and neo-classical details, which was in use as a restaurant in 2018. Stairs with a moulded timber handrail lead to the Apex Room on the first floor of the corner section and are accessible directly from the vestibule as well as from the gallery level of the hall in a flexible arrangement. It is a substantial entertaining space, largely free of structural pillars, with a coffered ceiling, neo-classical plaster mouldings and brackets. A club room with similar decorative treatment lies to the west.

Inside the main hall space, the overall effect is very similar to Olympia Grand Hall but much simpler, on a much smaller scale and with fewer decorative effects. The roof span of 30 metres (100 feet) by 72 metres (238 feet) and height of 24 metres (79 feet) remain substantial, but essentially constitute a reduced-scale version of the Grand Hall due to the design of barrel-vaulting over an unencumbered space with aisles and galleries surrounding on all sides.

Olympia Central created 250,000 square feet (23,225 square metres) of new space for Olympia, comprising three main exhibition floors of around 60,000 square feet (5,574 square metres) each and a service floor with entry and circulation at ground level, plus a basement beneath.

The façade of Olympia Central on Hammersmith Road is in the Modern style; the doors to the main entrance are not original. Horizontal strips of windows are designed to light the floors inside at a high level, avoiding obstruction by exhibition stands. A vertical panel of glazing rises above the low entrance, originally to light the light well just inside. The text 'Olympia' is written in relief at the top of each end of the façade, although '1929' in subscript has been lost following conversion of the top floor into a conference centre and closure of the central internal light well in 1987, which required addition of a new horizontal window at the top of the main elevation. The surface is also punctuated by small angle windows, other small windows and decorative air vents. The original decorative horizontal fixing bars for electric exhibition advertisements are retained. The original canopy extends most of the length of the façade, decorated and lit on the underside, and concealing floodlighting for the façade above.

Behind the front range are three exhibition floors above the ground floor service yard. The steel and concrete structure is expressed in the exposed west elevation, where brick elevations are functional, punctuated by near-continuous rows of high-level windows to allow maximum daylight to the exhibition areas within. These windows were originally lit by 'Maximum Daylight' glass, a combination of lens and prism layers intended to maximise light even on dull days, much of which appears to survive.

The interior reception area of Olympia Central has been significantly altered, including removal of the main stairs at ground floor and infilling of the light well above. However, the basement lift lobby which originally led to a basement restaurant is said to survive well. The exhibition floors were designed to be deliberately functional. The third floor has been modified to form a conference centre.