The Singapore Government’s Building and Construction Authority has a section on universal design guidelines. It has three key guides as well as other related information.
The 2016 Universal Design Guide for Public Places is a good practice guide for the built environment. It’s been well thought out and is presented clearly with many illustrations and drawings. This is a comprehensive guide that goes beyond basic accessibility requirements of previous guidelines.
The 2007 version of the Universal Design Guide has more detailed information including residential as well as public buildings.
The fifth version of the Code on Accessibility in the Built Environment introduced more accessibility and universal design. The first version was published in 1990 – long before many other countries.
Note that these digital documents are large and take time to download.