Vaa studied at the Norwegian National Academy of Craft and Art Industry and at Norwegian National Academy of Fine Arts from 1922 to 1923, under Wilhelm Rasmussen, and later traveled to Spain, Greece and Italy for studies.

In 1925, his first important work was a portrait of Minister of Education Ivar Peterson Tveiten (bronze.

[3] Further four bronze sculptures with motives from Norwegian fairy tales at Ankerbrua (Peer Gynt, Veslefrikk med fela, Kari Trestakk and Kvitebjørn Kong Valemon), and bronze wolves at Ila (1930).

Vaa contributed to the decoration of Oslo City Hall,[4] with the swan fountain in the courtyard (1948–1950).

He has made portrayal sculptures of several writers, Henrik Ibsen (1958, Skien), Aasmund Olavsson Vinje (1968), Ivar Aasen, and Olav Aukrust (1955, Lom), the fiddle player Myllarguten (Arabygdi, Rauland), sculptural work at the Nidaros Cathedral in Trondheim, several World War II memorials (Rjukan 1946, Nordfjord 1947, Porsgrunn 1950, Gjerpen 1954), and is represented at the National Gallery of Norway.