Enclosed balconies have become a thoroughly abused loophole in Vancouver's development industry. Their intended purpose was to provide an alternative amenity to outdoor balconies in places where it wouldn't make much sense or enjoy much use. Examples of the intended purpose would be for lower level dwellings on major streets, adjacent bridges with a lot of street noise, or in areas where there would be other factors that would mitigate the enjoyment of the outdoors. The enclosed balconies are exempt from a building's developable FSR, just as external balconies are, to a maximum 8% of a dwelling's floor area. So if you had a 1000 sqft condo you could expect an 80 sqft balcony since it would be "free" for the developer. Terraces and roof decks are not subject to the same calculation because they are treated differently, how I am not certain.
The enclosed balcony rose to prominence because a developer can sell it as an extra room, adding the square footage to the total for the dwelling, despite the fact that it was "free" for the developer to build, so far as their total developable density is concerned.
I tend to think that they are semi-useful spaces. Almost everyone I have ever met with one uses it either as an office or a room for their pet, (litter box, etc.). South or west facing enclosed balconies could also be used as a nice greenhouse, perhaps to help make those mortgage payments...
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