now on about 1,500,000 units annually to get to the 16 million housing units by 1970. (This is the same estimate for the decade which NAHB's Economics Department has suggested for some years. However, some of the components of this unchanged total have been revised.)

This is the most important part of the loss, amounting in the 1950-1959 period to over 260,000 units annually. This loss is easily definable in enumerating and cannot be, under normal circumstances, double counted or miscounted. The unit can be demolished only once! (This is not true of other changes in inventory, such as conversions or mergers, which could possibly include more errors in enumerating.)

During the 1940s the demolition rate was low. During the decade of 1950-1960 the demolition rate doubled to about 260,000 units annually. In the last three years in the 1950s the demolition rate increased to an annual rate of 260,000 units. It should be assumed that the demolitions will continue to increase over the rate of the 1960s.

This assumption is based primarily on the changing character of urban development. The low demolition rate of the 1950s was due to the housing shortage that still remained through the early and mid-1950s, and because of the sale house boom; this spread urban development mainly outward requiring little demolition in the central city core to make way for expanding downtown office and business space, or for new apartment buildings. Now, even during the early sixties, a more rapid rate of redevelopment at the fringes of downtown areas is readily visible in almost every major city with site clearances taking out substantial amounts of low and medium density housing to make room for both business and apartment construction.

This rapid spread of the suburbs was accompanied in many cases by inadequate planning, particularly in highway and street development. Consolidating the suburbs and providing adequate thoroughfares and rapid transit will no doubt require considerable demolition. Shopping centers and the like may also require some demolition of housing to provide for expansion and additional parking in order to accommodate increased density.

Loss Through Means Other Than Demolition

Losses included in this category form a second most important sector of removals. They were estimated at 203,000 units annually in the period of 1957-1959.

This category includes a variety of losses, such as through fire, by change in non-residential use, loss of houses which remain standing but are no longer inhabitable, and houses or trailers which are moved. These latter are selfcancelling for the U. S. as a whole, but not for localities as a house lost in this manner from one location, will be a unit gained for some other locality.

Table II presents annual losses by means other than demolition for the period of 1957-1959. It is estimated by the Census that the losses by fire, flood, and other casualties run as high as 83,000 annually, while there are over 70,000 units removed by abandonment. Third largest category are units changed from residential to non-residential use and vice versa.

Conversion is the process of making additional dwelling units out of the same structure for instance, making two apartments out of a two-story one-family dwelling. Merger is the reverse process.

Both of these factors are hard to enumerate and difficult to analyze. The data as presented by the Census have many limitations and should be used with caution. In any event, Census shows that conversions and mergers have a tendency over a period of time to eliminate each other. The relatively small difference (considering the inaccuracy of the estimates) between both figures in the latest period- 1957-1959 is not very significant. (Table III)

Conversions are assumed to have been high during the 1940s, about normal during the 1950s, and somewhat lower during the 1960s. Housing shortages, transition period, and

prosperity are the reasons behind these assumptions for the respective decades.

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Mergers mostly reversals of previous conversions regarded as having been: low during the 1940s; high during the 1950s; back to normal during the 1960s. The respective reasons: housing shortage, reversal of temporary conversions; a balanced market with greater competition for makeshift rental units.

ESTIMATES OF NET LOSS FOR 1960-1970

Estimates of replacement demand generated by removals from the housing stock indicate a need for 4.7 million units. Three factors go to make up the demand for new units (1) new household formations, (2) increase in vacant units, and (3) net removals. Revised estimates of this demand indicate an increase in the second and third factors and a downward shift in the first, over our forecast made at the beginning of the decade. During the '60s for every three units a builder erects one will go to replace a unit removed from the housing stock. Table IV sums up the estimates for the net removals by type of structure 3 million single family units will be removed, in addition, nearly 1 million units will be in structures with 5 more units, and about 800,000 will be in structures with 2 to 4 units.

The basic reasons for the high demolition rate during the 1960s can be arbitrarily placed in six categories:

(1) Urban renewal and slum clearance, (2) highway construction program, (3) increasing vacancy rate in older housing units, (4) increasing land costs, (5) better housing code enforcement and higher housing standards, and (6) increased losses resulting from fire, flood and other disasters.

Urban Renewal and Slum Clearance

Following World War II we embarked upon a housing program to provide housing units for all families and to upgrade the quality of housing. As a result of this effort, many cities have undertaken urban renewal and slum clearance programs. In 1961, for example, 37,000 units were demolished as a result of the 944 urban renewal projects under way; in 1962 this figure increased to 40,000 units and approximately 1,200 projects.

Highway Construction Program

For the decade we have set forth an ambitious highway program. Part of this program has been an intensive effort to improve the lot of the "suburbanite" who is demanding a rapid and safe way to work in the center city. With an increase in the number of miles of road being built in and around the cities we can expect an increase in the number of housing units destroyed.