As part of the conservation process for Singapore's shophouses, the Urban Redevelopment Authority has published detailed guidelines advising on conservation principles, compatible uses and possible refurbishments. The URA is particularly strict on historic districts, where the whole building has to be kept in pristine conditions, without any possible extensions.
Secondary settlements (eg. Geylang and Joo Chiat) are protected as well. However, the URA focuses there on the streetscape mostly and allows shophouse owners to build extensions at the rear, according to the maximum allowed height in the area. Residential historic districts (eg. Blair Plain and Cairnhill) as well as conservation bungalows can be modified with more freedom.
In all cases, the URA prescribes to follow three fundamental principles, known as the 3"R"s: Retention, sensitive Restoration and careful Repair. Selective replacement should only be considered when absolutely necessary. Regarding shophouses' use, they can be occupied by either commercial or residential tenants, as long as conservation of the building is maintained according to URA guidelines. The guidelines describe precisely all elements of shophouses to be safeguarded and provide local specification according to each neighbourhood.
For details on the guidelines, click to access the URA Guide on Conservation Shophouses.