Question: When did the roof gardens above the birthplace of Bill Grimsey open to the public?

full_context: Document 1: Bill Grimsey: William Grimsey (born 21 January 1952, in Kensington, London) is an English businessman who has specialised in the food and DIY sectors, most notably at Wickes, Iceland, and Focus (DIY).
Document 2: William Alfred Ismay: William Alfred Ismay or Bill Ismay (10 April 1910 – 13 January 2001) was a librarian, writer and collector in Wakefield, West Yorkshire known for his significant collection of post-war studio pottery. The collection called the W.A. Ismay Collection was bequeathed to the Yorkshire Museum and is one of the world's largest collections of 20th-century studio pottery. It includes work by Bernard Leach, Hans Coper, Shoji Hamada, Takeshi Yasuda, David Leach Dan Arbeid and Lucie Rie.
Document 3: W. W. Grainger: W. W. Grainger, Inc. is an American Fortune 500 industrial supply company founded in 1927 in Chicago by William W. (Bill) Grainger. He founded the company in order to provide consumers with access to a consistent supply of motors. The company now serves more than 3 million customers worldwide with offerings such as motors, lighting, material handling, fasteners, plumbing, tools, and safety supplies, along with inventory management services and technical support. Revenue is generally from business-to-business sales rather than retail sales. Grainger serves its over 3 million customers through a network of approximately 598 branches, online channels (such as Grainger.com, KeepStock and eProcurement), and 33 distribution centers.
Document 4: Department store: All the major British cities had flourishing department stores by the mid-or late nineteenth century. Increasingly, women became the major shoppers and middle-class households. Kendals (formerly Kendal Milne & Faulkner) in Manchester lays claim to being one of the first department stores and is still known to many of its customers as Kendal's, despite its 2005 name change to House of Fraser. The Manchester institution dates back to 1836 but had been trading as Watts Bazaar since 1796. At its zenith the store had buildings on both sides of Deansgate linked by a subterranean passage "Kendals Arcade" and an art nouveau tiled food hall. The store was especially known for its emphasis on quality and style over low prices giving it the nickname "the Harrods of the North", although this was due in part to Harrods acquiring the store in 1919. Other large Manchester stores included Paulden's (currently Debenhams) and Lewis's (now a Primark).
Document 5: Kensington Roof Gardens: The building housed the department store Derry and Toms until 1973, and then Biba until 1975. Since the 1980s the garden has been used as a restaurant and club.
Document 6: Department store: The iconic department stores of New Zealand's three major centres are Smith & Caughey's (founded 1880), in New Zealand's most populous city, Auckland; Kirkcaldie & Stains (founded 1863) in the capital, Wellington; and Ballantynes (founded 1854) in New Zealand's second biggest city, Christchurch. These offer high-end and luxury items. Additionally, Arthur Barnett (1903) operates in Dunedin. H & J Smith is a small chain operating throughout Southland with a large flagship store in Invercargill. Farmers is a mid-range national chain of stores (originally a mail-order firm known as Laidlaw Leeds founded in 1909). Historical department stores include DIC. Discount chains include The Warehouse, Kmart Australia, and the now-defunct DEKA.
Document 7: Richard Grisé: Richard Grisé (born 15 January 1944 in Saint-Bruno-de-Montarville, Quebec) was a member of the House of Commons of Canada. He was a businessman and life insurance broker by career.
Document 8: Department store: The design and function of department stores in Germany followed the lead of London, Paris and New York. Germany used to have a number of department stores; nowadays only a few of them remain. Next to some smaller, independent department stores these are Karstadt (in 2010 taken over by Nicolas Berggruen, also operating the KaDeWe in Berlin, the Alsterhaus in Hamburg and the Oberpollinger in Munich), GALERIA Kaufhof (part of the Metro AG). Others like Hertie, Wertheim and Horten AG were taken over by others and either fully integrated or later closed.
Document 9: G.W. Scott and Sons: G.W. Scott and Sons was a producer of fine wickerwork crafts, basketry, and luxury leather goods, founded in 1661 in the city of London, England, in the United Kingdom. The company ceased production in 1967.
Document 10: Francis Grimston: Francis Grimston was educated at Harrow and Magdalene College, Cambridge. At Cambridge, he was a member of the University Pitt Club. As a cricketer, he was mainly associated with Cambridge University and Marylebone Cricket Club (MCC), making 18 known appearances in first-class matches from 1843 to 1851. He was a wicket-keeper.
Document 11: Neues Schauspielhaus: While the auditorium was destroyed in World War II, the facade as well as the cinema survived and in 1951 was renamed the Metropol. Since 1977 it has been used as a discothèque and became a famous music club during the 1980s heyday of West Berlin, frequented by bands like Depeche Mode, Morrissey, The Cross, The Human League and Front 242. For a short time in 2000 it was the location of the KitKatClub and in 2005 the architect Hans Kollhoff remodeled the interior as the "Goya" night club.
Document 12: Department store: The middle up segment is mainly occupied by Metro Department Store originated from Singapore and Sogo from Japan. 2007 saw the re-opening of Jakarta's Seibu, poised to be the largest and second most upscale department store in Indonesia after Harvey Nichols, which the latter closed in 2010 and yet plans to return. Other international department stores include Debenhams and Marks & Spencer. Galeries Lafayette also joins the Indonesian market in 2013 inside Pacific Place Mall. This department store is targeting middle up market with price range from affordable to luxury, poised to be the largest upscale department store. Galeries Lafayette, Debenhams, Harvey Nichols, Marks & Spencer, Seibu and Sogo are all operated by PT. Mitra Adiperkasa.
Document 13: Department store: All major cities have their distinctive local department stores, which anchored the downtown shopping district until the arrival of the malls in the 1960s. Washington, for example, after 1887 had Woodward & Lothrop and Garfinckel's starting in 1905. Garfield's went bankrupt in 1990, as did Woodward & Lothrop in 1994. Baltimore had four major department stores: Hutzler's was the prestige leader, followed by Hecht's, Hochschild's and Stewart's. They all operated branches in the suburbs, but all closed in the late twentieth century. By 2015, most locally owned department stores around the country had been consolidated into larger chains, or had closed down entirely.
Document 14: Plymouth: In 2004 the old Drake Circus shopping centre and Charles Cross car park were demolished and replaced by the latest Drake Circus Shopping Centre, which opened in October 2006. It received negative feedback before opening when David Mackay said it was already "ten years out of date". In contrast, the Theatre Royal's production and education centre, TR2, which was built on wasteland at Cattedown, was a runner-up for the RIBA Stirling Prize for Architecture in 2003.
Document 15: Sainsbury's: J Sainsbury plc, trading as Sainsbury's, is the second largest chain of supermarkets in the United Kingdom, with a 16.9% share of the supermarket sector in the United Kingdom. Founded in 1869, by John James Sainsbury with a shop in Drury Lane, London, the company became the largest grocery retailer in 1922, was an early adopter of self - service retailing in the United Kingdom, and had its heyday during the 1980s. In 1995, Tesco overtook Sainsbury's to become the market leader, and Asda became the second largest in 2003, demoting Sainsbury's to third place for most of the subsequent period until January 2014, when Sainsbury's regained second place.
ground_truth: 1980s
sub_queries: Bill Grimsey >> place of birth Answer: Kensington
when did the roof gardens above Kensington open to the public Answer: 1980s