What explains the difference between parcel and home nonconformance rates?

Neighborhoods Roslindale Square
1

The Roslindale map shows that 67% of parcels are nonconforming today, but only 35% of existing homes are nonconforming.

Can you explain this?

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2

Great question! “Nonconforming homes” refers to the number of homes that already exist but exceed capacity constraints set by zoning. As a result, they would not be allowed to be rebuilt today without a zoning variance from the ZBA.

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Say there’s a 3-family home built before single-family zoning was implemented. Now that parcel is non-conforming because it exceeds the capacity limitation with 2 non-conforming homes.

In addition to exceeding capacity constraints, a parcel can be considered non-conforming for a number of reasons. In the tool, the other type of non-conformance that is calculated is when the ratio of the building square footage to the lot size exceeds the maximum Floor Area Ratio (FAR) defined in zoning.

3

Sorry, but I’m still not understanding how the nonconformance rate for parcels is 30% higher than for homes? I’m sure it’s some basic math step that I’m missing?

4

All good–I agree it’s a bit confusing. Despite the similarly-named metric, they measure different (but related) things.

This is how they are calculated:

Parcel non-conformance rate = ([# of parcels that exceed allowed floor area] + [# parcels that exceed capacity allowance] + [# parcels that exceed both]) / [# total parcels]

Percentage of non-conforming homes = ([# existing homes on parcels that exceed capacity allowance] - [# of homes allowed by zoning]) / [# total homes]

To illustrate the metrics, say we have the following 5,000 sq ft parcels in a single family zone with an allowed FAR of 0.5

  1. 3,000 sq ft single-family (FAR 0.6)
  2. Duplex, each 2000 sq ft (FAR 0.8)
  3. 2,000 sq ft single-family (FAR 0.4)

Only parcel #3 is conforming with zoning. As a result, the parcel non-conformance rate is 2 non-conforming out of 3 total, so 66%.

Each parcel allows only for a single home and parcel 2 has 1 excess home. Hence, the 1 out of 4 homes or 25% would require a zoning variance to be rebuilt. Parcel 1 would require an FAR variance, but not a capacity one.