The completed £13.5m expansion of east London's Whitechapel Gallery is expected to open 5 April.

The gallery, re-designed by Belgian architects Robbrecht & Daem and Witherford Watson Mann, is almost double the size after it merged with the adjacent Passmore Edwards library (built in 1892) increasing the 3,000sq ft space by 78 per cent. New features include three galleries dedicated to international art collections, new art commissioned by the gallery's trust and an archive collection and a research room to document the last 100 years of the gallery and local area. Other new facilities consist of an education and research tower for local school and community groups as well as a street-facing café. Contractor Wallis, who worked on the redevelopment of the V&A Museum of Childhood, is carrying out the construction work.

The project is being funded by the Heritage Lottery Fund, the London Borough of Tower Hamlets, Arts Council England, the European Regional Development fund, London Development Agency. Nearly £2m has been raised from charitable trusts and individual donors and £2.5m from an auction of donated artworks. A gallery spokesperson said: "The development of the Whitechapel Gallery was much needed: previously the gallery had to close for up to 10 weeks each year to allow for exhibition installations. The gallery’s former Education Studio could not accommodate full class sizes and the overwhelming number of schools wishing to use its facilities. Previously there was limited access for disabled people to the gallery and there was no wheelchair access to the former library."

The gallery was built in 1901, according to the design of Charles Harrison Townsend, to bring art to the East End population. It was the only gallery to showcase Picasso’s masterpiece Guernica in Britain and presented the first major British show of American abstract expressionist Jackson Pollock in 1958. In the 1970s, David Hockney, Gilbert & George and Richard Long had their first works of art displayed at the gallery. Details: whitechapelgallery.org