"Greater productive capacity in the construction industry to meet the demands of an expanding population must be provided by increases in efficiency in the processes and techniques of designing and building. An ultimate objective is the development of a system of construction in which all materials, components, products and equipment fit together simply and easily with minimum alterations required on the job."

With this statement, the editors of Modular Practice, published in 1962 by John Wiley & Sons, Inc., introduced the concept of modular coordination to the reader. This statement is even more to the point today, since the use of modular coordination in the design and construction of buildings not only increases production but can also result in significant cost savings.

This year marks the 35th anniversary of a meeting called by the American Standards Association (now the American National Standards Institute) in August 1938, from which the development of the principles of modular or dimensional coordination stem. This conference, called to explore the need for setting up a project on modular coordination, was attended by representatives of the various facets of the building industry, including the Brick Institute of America (then SCPI). Their unanimous recommendation to ASA was that such a project be initiated. This was effected in 1939 as ASA Sectional Committee A62 on the Coordination of Dimensions of Building Materials and Equipment, under the sponsorship of the American Institute of Architects and the Producers' Council, Inc. This committee currently operates under the name of ANSI Standards Committee on Pre-Coordination of Building Components and Systems, although at present it is without sponsorship.

During the past 35 years many organizations have contributed to both the technical and educational aspects of the project, including the Federal Government, American Institute of Architects, American Society of Civil Engineers, Associated General Contractors, Consulting Engineers Council, National Association of Home Builders, Prestressed Concrete Institute and many trade associations representing producers of building products and components manufactured to predetermined sizes.

The Modular Building Standards Association was organized in 1957 by the American Institute of Architects, Associated General Contractors of America, National Association of Home Builders and the Producers' Council, Inc. It was supported by those organizations plus individual memberships. MBSA worked with the Building Research Advisory Board (BRAB), National Academy of Sciences-National Research Council in the preparation of a manual on modular design. The project was carried on under a grant from the Ford Foundation's Educational Facilities Laboratories, Inc. This manual, Modular Practice, is the one quoted at the beginning of this Technical Notes and is still the most comprehensive treatment of the subject available.

Since the organization of ANSI Standards Committee A62, BIA has been represented on the committee and has participated in the development of the following standards: (Copies of these standards available from American National Standards Institute, 1430 Broadway, New York, N.Y. 10018.)

Currently, a large percentage of brick is produced in modular sizes and, consistent with its long established policy, BIA recommends modular design and the use of modular products as a means of reducing building costs.

The sizes of modular brick listed in Table 1 are typical of those generally produced by the industry. However, as design requirements change, new sizes may be added and less popular sizes dropped. Also, few manufacturers produce all of the sizes listed. Therefore, it is recommended that the designer consult current manufacturer or regional catalogs for available sizes in any locality before proceeding with a design.

Tables for use in estimating quantities of modular brick and mortar are given in Technical Notes 10 Revised, "Estimating Brick Masonry".

The listed dimensions of modular masonry units are "nominal'', and are equal to the manufactured or specified dimension plus the thickness of the mortar joint with which the unit is designed to be laid, as indicated in Fig. 1. For example, the manufactured length of a unit whose nominal length is 12 in. would be 11 1/2 in. if the unit were designed to be laid with 1/2 in. joints, or 11 5/8 in. for 3/8 - in. joints.

The manufactured dimensions of a single unit may vary from the specified dimensions by not more than the permissible tolerances for variation in dimensions included in the applicable ASTM specifications.

In Table 1, all dimensions are nominal and the standard mortar joint thickness is determined by the type and quality of the product, particularly by the permissible variation in dimensions. In general, facing brick are laid in either 3 3/8 - in. or 1/2 - in. thick mortar joints, although some products, such as ceramic glazed brick or structural clay facing tile, are designed for 1/4 - in. thick mortar joints.

The manner in which the coordination of different modular masonry units is accomplished is shown in Fig. 2. The exterior facing brick are shown with 3/8 - in. joints and are backed up with units, such as structural clay tile, designed for use with 1/2-in. joints. The inside facing of ceramic glazed units are laid in 1/4-in. joints. The full coordination between units is apparent, as indicated in the enlargements. The thickness of the vertical joints between the different types of units is the average of the joint thicknesses used with each unit.

The authors of Modular Practice emphasize the importance of establishing the 4-in. modular grid as a reference system for the three dimensional elements of plan and structure, but state that no part of the plan should be forced to fall on the grid, nor should any dimension be forced to be multiples of 4 in. However, they also point out economies that can be effected in construction costs through the use of modular dimensions, thus minimizing the altering of predimensioned components at the job site.

Figure 3 shows grid locations of mortar joints in walls constructed with various modular units when the walls are centered between grid lines. It can be seen that all grid lines coincide with horizontal mortar joints for only the 2 - in. and 4 - in. nominal heights, thus providing 4 - in. flexibility.

With the 2 2/3 - in. high units (as well as 8 - in. high units), grid lines coincide with horizontal joints every 8 in. If 4 - in. flexibility is required, a course of 4 - in. high supplementary units (or a rowlock header course) must be used.

The fact that alternate grid lines coincide with the mortar joints when the 2 2/3 - in. high brick is used provides a simple rule for determining the location of a grid line with respect to the masonry at any point above or below a given reference grid line. Any grid line which is an even multiple of 4 - in. from the reference line will have the same relative position with respect to the masonry coursing, while any grid line that is an odd multiple of 4 in. will have the alternate position. This simple rule greatly simplifies the checking of course heights, particularly for lintels, where it is usually essential that the head of the opening coincide with a horizontal mortar joint.

A symmetrical grid location for walls is usually preferred to an unsymmetrical position. The correct symmetrical location (centered between grid lines or centered on a grid line) will often be influenced by the length of the masonry units to be used.

With masonry units whose nominal lengths are 8 or 16 in., vertical (head) joints will occur on grid lines when 4 and 8 - in. thick walls are centered between grid lines, and they will occur at mid - grid points when these walls are centered on grid lines.

The above conditions are also true for 12 - in. nominal length units when they are laid in one-third bond. However, when these units are laid in center (1/2) bond, vertical joints in alternate courses will occur on grid lines and be centered between grid lines.

As this is written (May 1973), it is anticipated that Congress will pass legislation which would create a National Metric Conversion Board to plan and coordinate a voluntary conversion process in which, over a period of some ten years, the United States will ''go metric". It is highly probable that modular or dimensional coordination will be made an integral part of metrication in the construction industry, as it was in Great Britain when it made the decision to convert to metric about eight years ago. It is expected that, if this comes to pass, the acceptance and use of modular coordination will increase at a much more rapid pace than it has under the evolutionary process it has been permitted to follow for the past 35 years.