I bought an old semi-D and want to do a renovation. More or less same scopes like your case, i.e. extensions for both front and back, redesign the room layout. and etc.

I understood DBKL approval is required once there is a change of external. To obtain DBKL approval, you can hire (1) an architect (2) a draughtsman.

I designed my own layout and have asked a few contractors to quote the prices. I thought I could save some money by hiring a contractor who could also offer the services of a draughtsman to draw the plan and submit to DBKL. However, the magnitude of the differences for the prices quoted by the contractors were quite big. The highest was 4 times of the lowest. One of the contractors (who is a forum member) here advised me to engage an architect. Draw up the technical drawing so that I could get apple-to-apple comparison.

So, I engaged an architect who is also a forum member here. He is helping me with the design and structure engineering with a bit of ID. I have viewed his design and like the ideas proposed. Once he completes his final design, I will invite the contractors to quote again.

Therefore, if you are going to spend a few hundred K for your renovation (in view of your scope), I think it is better to find a talented architect who could offer you more than technical drawing, DBKL approval and the final CCC. The investment of his/her services would help to add values to your house.