In short: Regularisation is the formal process of getting BCA approval retroactively for a building structure that was constructed, modified, or extended without prior approval. In Singapore, owners discover unauthorised structures most often when they try to sell, refinance, renovate, or face an enforcement notice. Regularisation typically takes 4 to 12 weeks and ranges from S$2,500 to S$20,000+, depending on complexity. Unaddressed unauthorised structures can result in BCA