Yes you must get a building permit from the city building services. The cost of the permit is based on the estimated building cost of the addition (typically a sliding scale). The city building services can tell you what is permitted in the local zoning laws. Start there.
I have an attached rowhouse that has about 650sq.ft living space. The only way that I can add value to this small house is to extend one of the bedrooms backward - which means extending the 2 side walls and removing the back wall and pushing it 5 to 7 ft. Currently lady (owner) has some temporary shade in the empty space and some storage articles in it. There is another attached rowhouse from behind.
My Questions are -
Do I have to check [pull permit ?] with the city office for this type of extension to see if they allow this or not ?
How much would be costs involved in doing this ?
Can I just extend only the bedroom ? I fear that if I start extending the bedroom, it would kinda snowball to extending the other floors [which will snowball costs] ?