Larouche – Court of Quebec determines the relative business use represented by a home office using the home’s gross rather than net area

In deducting his home office expenses, the taxpayer determined the portion of his home that was used in his business of providing electrical engineering services, which he calculated by dividing the square-foot area of the three rooms that he used in that business by the net square footage of his home, which was the area of the two floors as measured by the exterior dimensions, minus the areas taken up by the walls and minus the area of common areas (stairwells and hallways). In instead accepting the ARQ method, which divided the area of the three rooms by the gross floor area, Brunelle JCQ stated (at para. 35, TaxInterpretations translation):

[A] person's home is first and foremost the individual’s dwelling and "the privileged place of his or her private life". Admittedly, a person may choose to work at home and reserve a certain amount of space for this purpose, but the fact remains that corridors, stairwells and other indoor areas for locomotion are essential to the personal use of the premises.

Neal Armstrong. Summary of Larouche v. Agence du revenu du Québec, 2023 QCCQ 3350 under s. 18(12).