In terms of public architecture, a prominent contribution is the Land Bank building in Pretoria and the Conservatoire of Music (1960) at North-West University described by Federico Freschi as a "a sculptural tour de force in the Brazilian idiom".
The resultant buildings and places celebrated land- and cityscapes with which they were contextually interwoven and expedited the development of a South African way of architectural thought, based on and advocating a contemporary worldview.
The same values, fuelled by a love of history, language and country, found expression in restoration work, such as at Paul Kruger’s farm house at Boekenhoutfontein, where he paid tribute to past achievements, and also in houses and bigger buildings, such as the Land Bank building in Pretoria, where again he was true to the present – the time in which he lived and worked.
Closest to his heart was possibly the building of churches and his pursuit was for a worthy and meaningful architecture embracing worship.
De Ridder’s three principles, applied to both religious and secular buildings, were firstly that the architecture should be contemporary, secondly that form should emerge from the meaning of the function and thirdly that the structure should be economic and affordable.
As an architect, he had the rare experience that his designs remained appreciated and current in his lifetime, and are still being studied and analysed as historically significant in a quest for authenticity.
His work was published widely in South Africa and also internationally in both acknowledged academic journals and more popular monthly architectural magazines where his ideas and decisions are revisited and re-evaluated.