You must calculate the percentage of the income and expenses you want to claim based on the square footage of the building that you are occupying and renting out.
As per Canada Revenue Agency: Completing Form T776, Statement of Real Estate Rentals
If you rent part of the building where you live, you can claim the amount of your expenses that relate to the rented area of the building. You have to divide the expenses that relate to the whole property between your personal part and the rented area.
You can split the expenses using square metres or the number of rooms you are renting in the building.
For example, if you rent 4 rooms of your 10-room house, you can deduct:
100% of the expenses that relate only to the rented rooms, such as repairs and maintenance of the rooms, plus
40% (4 out of 10 rooms) of the expenses that relate to the whole building, such as taxes and insurance.
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