When I grew up in Houston in the 1950s, few people had ever heard of a "town house." You lived either in detached single-family houses or in apartment buildings. "Row houses" were considered an inferior species of residence, found only in older, presumably blighted sections of eastern cities such as Philadelphia, New York, Baltimore or Boston.

Perceptions changed when inventive merchandisers started calling row houses town houses. Although row houses derived historically from high-density urban precedents in Europe and colonial America, they seemed perfectly suitable, once renamed, for locations outside of central cities. Thus today's "town houses" often are not in town at all.

Developers, architects and land planners long have realized that "attached" housing means increased densities and economies by comparison with traditional subdivision development.

Yet attached housing, unlike many types of apartments, still can provide most of the basic amenities associated with subdivision homes. In fact, attached housing offers significant aesthetic opportunities for building and streetscape design, opportunities difficult to exploit with detached homes.

Attaching houses creates larger residential building masses that can aspire to collective grandeur and presence exceeding the sum of individual parts. Yet dwellings still can have their own identity, expressed through appropriate roof, facade and entrance gestures within the overall composition of the continuous housing form. This can occur whether there are two, 10 or even dozens of houses in a single row.

Unfortunately, many contemporary town-house developments consist of buildings that are nothing more than incoherently assembled rows of units. Dwellings between party walls shift back and forth at will while bumping up or down as topography dictates. Colors, materials, fenestration, ornamentation and roof shapes may vary randomly from unit to unit.

But well-designed rows or blocks of attached housing, by virtue of their size, extendability and disciplined facades, can contain, define and shape exterior spaces -- linear streets (such as those in Northeast D.C., Capitol Hill, Georgetown or Alexandria), courtyards, gardens, village greens or urban plazas (such as those in Paris or in Reston's Lake Anne village center).

In cities where block and street patterns are clearly established, contiguous row housing fronting streets and lining blocks reinforces such patterns. And it is these patterns, projected into three dimensions, that can provide a recognizable sense of identity and place, a public urban image that transcends the individual house or property owners. Thus, attached housing is potentially more public spirited in its visual contribution to city space and place making.

Remarkably high densities can be attained with attached housing, even when it departs from traditional row geometry. Ten to 12 units per acre, along with related parking, drives and roads, is typical of town-house zoning in many jurisdictions.

But much higher densities -- 15 to 20 units per acre -- are possible as dwelling footprints, lot size, yards and streets are made smaller. High on-site parking ratios (sometimes as much as 1.5 or 2 cars per unit), more than any other factor, push effective housing densities downward.

Accompanying increased density is increased efficiency in site infrastructure -- paving for streets and sidewalks, utility mains and landscaping. The more dwellings on a street or parcel, the less the infrastructure costs per unit, all other factors being equal. And it could be argued that with proper design, individual dwelling unit security is higher because of both actual and potential collective surveillance, a kind of "safety in numbers" psychology.

To many designers and homeowners, reducing the size of traditional front yards is a desirable objective. More lot area can be dedicated to private use -- usually at the rear -- for terraces, gardens and play areas away from public streets and firmly under the control of the occupant. Common or public spaces in front then can be used collectively and maintained by municipality or homeowner association, while homeowners themselves are spared from weeding and mowing front lawns on fair-weather weekend days.

Unquestionably, each square foot in an attached house costs less than a square foot in a detached home. Shared walls and foundations between units, called "party" walls, result in less exterior wall surface, in turn reducing the amount of insulation, windows and exterior cladding required for each dwelling unit. The relative compactness and reduced exterior surface area of town houses lead to reduced energy consumption and lower utility bills when compared with detached housing.

Construction of attached housing can be systematized, possibly yielding additional savings in construction labor, materials and overhead. With construction savings, plus savings in lot and lot improvement costs based on increased density and infrastructure efficiency, the total development cost of an attached housing unit, for a given amount of floor space, is substantially less than that of conventionally detached housing.

But attached housing has disadvantages. Party walls are one potential source of trouble. If they are not massive and airtight, sound will leak through them. Even with solid, heavy masonry party walls, impact noises and other structure-borne sounds may be transmitted audibly from one dwelling to another. There's nothing quite like having your neighbors' stereo speakers backed up to the wall against which you've placed your bed.

Unit-to-unit privacy also may be compromised simply because of window proximity in exterior walls. If adjacent windows of neighboring units are only a few feet apart, and if both are open during fair weather, eavesdropping becomes unavoidable. Your neighbor's cookout, or patio party, its sounds and smell, may invade your domain. Likewise, you may be able to observe, perhaps involuntarily, everything going on in neighboring yards or courts overlooked by your upper-story windows.

Sometimes, attached housing is configured so that windows in one unit directly face windows of another unit only a short distance away. This, too, can be distracting to residents concerned about both visual and acoustic privacy. There are dimensions of separation that most people perceive as too small -- less than about 20 feet -- while window-to-window distances of 30 feet or more seem more comfortable, more protective.

It's generally harder to build additions to attached houses as household size, activities or affluence increase. When feasible, additions usually can be constructed only at the back, away from the street. With limited lot area, or setback constraints prescribed by zoning, such extensions may be undesirable or impossible. Further, front or back extensions additionally deepen the dwelling unit, perhaps cutting off existing rooms from light, air and view. For this reason, architects often design town-house additions to be relatively "transparent."

In recent years, as attached housing has gained wider and wider market acceptance, builders and designers have looked for new ways to combine dwelling units. Innovative housing types have evolved -- duplexes piggybacked over flats, fourplexes and sixplexes, corner-turning town houses. Much of the effort has focused on the product -- the building and the unit within.

Unfortunately, sometimes not enough effort is focused on site planning, on the shaping of public spaces -- streets, squares, courts -- edged and defined by these buildings. Too often, rows of attached housing seem scattered about, serving only to separate one parking lot from another. Instead, town houses, whether in rows or otherwise, should add up to form "townscapes."

NEXT: Garden apartments and how they grow.