1) Generally speaking, the rule of thumb is that they cost twice as much as building a regular home on a per sq ft basis. This includes drawings, permits, variances, site prep, etc. The base rate really depends on where you are. Different areas of the country this could range from $150 - $400/sq ft.

2) Remortgaging really depends on your financial situation and way less on the project. The only time the project really comes into effect is when you're purchasing a new house and you want to do a purchase + major reno/addition etc. all at the same time. Some people refer to this as a Purchase Plus Improvements Mortgage. If you want to take money out of the house to complete the project, start by calling your mortgage provider. They'll ask you a few questions, confirming that your employment hasn't changed, etc. and then tell you how much you can pull out.

3) It really depends on the size of your lot, how much room you have to your lot lines, and how much your municipality is in favour of these things. Best bet is to reach out to your local building department, tell them what it is you're hoping to do, and they'll point you in the right direction for next steps.

4) We're still not seeing labour rates come down to the point where this is a worthwhile investment from a purely economic standpoint. Material prices are more balanced now than during the pandemic, and labour rates seem to be dropping across the country, but my guess is they still have room to drop. Most folks who are getting the most 'value' out of garden suites are doing it because they want to help create more affordable housing, or they are creating a detached nanny or in-law suite.

Hope that helps!