This building holds value and information that contributes to an understanding of the planning and design principles of the Don Mills community.

The property sits on a ridge which overlooks Leslie Street and Wilket Creek Park. The visibility of the building from Leslie Street is not clear due to its deep setback and low-rise building height. To the east of the property is the Don Mills Trail which used to act as a Canadian National Railway Spur Line.

The high levels of glazing, simple forms and lack of ornamentatio are properties of International Style. The overall building is strongly designed of Modernist style architecture. 

The property was identified as having cultural heritage value in the inventory included in North York's Modernist Architecture, first published in 1997, with a revised edition in 2009.

Located on the east side of Leslie Street between Eglinton Avenue East and Overland Drive, the property at 1135 Leslie Street contains the former Peacock & McGuigge building designed by Gordon S. Adamson Associates in 1959. The property contains a one-storey building with a flat-roof extended to overhang the fully glazed principal (west) elevation with white brick walls on the side (south) elevations. Originally the brick cladding on the south elevation was only interrupted by a single recessed entrance but, with the extension to the east, now includes additional full-height windows which replicate the original proportions of the principal glazed elevation. The building was the office headquarters for the construction company started by Kenneth Peacock and Donald McQuigge which built roads in southern Ontario. It is currently owned by Crestview Group of Companies (originally known as the Lawrence Construction Company) which for 90 years has developed rental apartment building projects in Toronto. The development of the site resulted after the extension of Leslie Street to Eglinton Avenue East in 1958.

Statement of Cultural Heritage Value

With its substantially landscaped setback and finely detailed International Style architecture, located on a curvilinear extension of Leslie Street, the former Peacock and McQuigge building has design value as an excellent representative of the Don Mills office headquarters typology. The setting surrounds the building with open space, a deep setback from the street and locates parking at the rear of the property with extensive tree-planting and shrubs. The design of the building is a fine representative of the International Style with its fully-glazed principle (west) elevation, with equal bays of narrow steel columns flanking dual panels of glazing, contrasting with the originally fully brick-clad side elevations, broken only on the south side by a narrow entrance. The characteristic flat roof extends in a deep cantilever in a rare International Style acknowledgement of building orientation and was matched by a projecting stone base which extended along the sides.

The former McQuigge & Peacock headquarters has cultural heritage value as it is historically associated with the 1950s planning and development of Don Mills by E. P. Taylor and Don Mills Developments Ltd. with the lead planner Macklin Hancock which was a notable example of Post-War suburban planning based on Garden City principles and encouraged the establishment of businesses to the south of the residential neighbourhood as part of a goal for self-sufficiency and local employment. It is also valued for its association with the firm of Gordon S. Adamson Associates who from the late 1940s were leading modernist architects in Toronto and were also responsible for the William Wrigley Jr. Co. building constructed at 1135 Leslie Street in 1962. The building is valued for its association with the Massey Medal awards as it was a finalist in 1961.

Although not part of the original plan for Don Mills, the property at 1135 Leslie Street has contextual value as its low-rise, modernist building in a landscaped setting represent the two design principles that define the mid-20th century Garden City values of the Don Mills development. It maintains and defines the character of the area and is visually, physically and historically linked to its surroundings in this part of Don Mills as it developed through the1950s-1960s establishing its landscaped campus headquarters character.