I want to add my common-law spouse on to the title of my property. Someone said that I should not have to pay any Property Transfer Tax. Can you confirm this?

In order for your common-law spouse to be exempted from the Property Transfer Tax, they and the property would first have to meet a number of criteria.  You did not state whether this was your principal residence or not, but assuming that it is your principal residence which is a single family dwelling with no commercial portion, you must have lived in the property for at least 6 months immediately prior to the transfer, the property must be 1.24 acres or smaller in size and you must have been living and cohabitating in a marriage-like relationship with your common-law spouse for a continuous period of at least two years.  If all of those criteria are met, the tax should not apply