There is a philosophical discussion within the New Urbanism about how best to write codes. This debate among friends is about two successful approaches to codes for development and zoning.
DPZ in general and Andres Duany in particular are famously allergic to the idea of curtailing possibilities. They generally like to err on the side of being permissive. This leads them to write codes so that any combination of the permitted building envelope and internal function is allowed. Another approach is to code building types so that the compromises necessary for comity among neighbors are built in at the building-type level, rather than the lot-level. Stefanos Polyzoides is the most vocal proponent of that second method, which came to debate at the CNU in 2012.
The Transect and Interior Lot Lines
New Urbanists typically map zones on both sides of each street, so that each street has a coherent look and feel. Naturally, the zones change at mid-block. Different zones, then, face each other across interior lot lines and alleys. For instance, a T5 main street will often have T4 or even T3 behind it. (The Rural-to-Urban Transect has its own website.)
A code that regulates by building type, however, can require buildings that extend beyond their neighbors’ back walls to have a wider side yard or otherwise mitigate their own impacts. If building types are regulated independently of their lots, then a building type that is likelier to prove a nuisance to its neighbors can be specially regulated to avoid doing so. Although the Model SmartCode must be calibrated for each locality, it is primarily concerned with the frontage. The un-calibrated SmartCode allows full-height building envelopes to extend almost the length of the lot.
Image courtesy of the Center for Applied Transect StudiesFor example, Table 15B of the Model SmartCode (for T4) shows that the Principal Building can extend to within 3 feet of the rear setbback. The procedure for calibrating the SmartCode requires that this is revisited for each locality, of course, but it is nevertheless clear that the intention is to allow each property owner a great deal of lattitude. It should also be noted that up to 70% lot coverage is permitted under the Model SmartCode, so that would restrict the envelope a bit more on large lots. If greater light and air are needed on the sides or rear, the planners calibrating the code must restrict the envelope to do so.
Metrics and Types
Although this issue can be resolved by adding new metric requirements, it does begin to show one of the advantages that coding by types offers. If planners were to code by type, they could code to precisely the desired level of specificity. For example, suppose regulation A were to apply only to buildings (as opposed to houses). Suppose, as well, that regulation B were to only to apartment buildings, and regulation C were to apply only to dwellings — in whatever kind of building or house. In that case, only regulation B would apply to an office building, regulations B and C would apply to an apartment building, and only regulation C would apply to a house with a dwelling unit.
In order to do this, though, building types have to be treated as primary. In the SmartCode, building types are not regulated directly. They are regulated by the combination of their disposition on the lot, their internal configuration, and their internal function(s). Although this allows frontages to be regulated separately from the internal function it treats all instances of the same function — e.g. Dwellings — the same.
It is interesting to contemplate how far type-based regulation could go, and whether it might offer special advantages. First, it may be possible to specify even distances and the sizes of spaces according to proxemics. A “front yard” that is a “social distance” from the sidewalk would then be 12-25 feet deep. Second, it may offer a way to ensure that buildings and places are more legible, by using types that are commonly understood: “apartment building” is more comprehensible than a building envelope that happens to have dwellings inside of it. Third, it offers a ready (and traditional) way to tailor regulations to exactly the level most appropriate. “Bay Windows” are often exempted from setback requirements, for example.
None of these ideas is at all new, but it may be useful to investigate potential of the greater use of types of structures, building types, and parts of buildings.