Last week I wrote about Toronto's plan to make fourplexes as-of-right across the city, but also why this form of missing middle housing shouldn't have a maximum floor space index.

Today, let's look at the numbers in a bit more detail.

If you look at a zoning map of Toronto, you'll see that many neighborhoods across the city have a maximum floor space index (FSI) of 0.6. What this means is that if you have a piece of land like this:

• Lot width: 20'

• Lot depth: 115'

• Site area: 2,300 sf

Your total allowable gross floor area would be 1,380 square feet (0.6 x 2,300 sf).

If you build a laneway suite in this city, that won't count towards your total allowable GFA (otherwise they'd be very challenging/impossible to build). But if you want to build something like a triplex or a fourplex, it counts.

The one important caveat is that if you're building a residential building -- that isn't an apartment building with 5 or more homes -- you can deduct the floor area of the basement:

This, of course, helps the situation. But it doesn't solve all of our problems.

If you assume that the basement can be one home, that still only leaves 1,380 square feet for the other three, technically permissible, homes. This equals: 3 homes x 460 square feet.

Another option would be 2 homes x 690 square feet. But still, we're not exactly making it easy to deliver more "family-sized homes" in the city.

And herein lies one of the problems (plural, because there are others). We can say that fourplexes are allowed across the city, but it may not actually be technically feasible or practical to build them.

Note: I am not a planner. If you are, leave a comment below.