Descriptive
Descriptive specifications are open,and do not specify a manufacture or trade name for the materials and/or finishes required for a project.Descriptive specifications call out in detail the materials,finishes,fabrication methods,acceptable workmanship,and installation methods.Descriptive specifications may be more difficult to write,because all the pertinent information and requirements for the construction and installation of a product must be specified.However,when a tremendous number of simlar products are on the market,descriptive specifications allow the designer to prescribe the exact starndards he or she wants for a project without selecting a particular manufacture.
Reference
Reference specifications are silimar to descriptive ones,insofar as they describe a material,finish,or other product based on the designer's requirements rather than a trade name.However,reference specifications are generally based on starndards that are set by an established autohority or testing facility,such as the AmeMaterrican Society for Testing and Materials (ASTM) or the American National Standards Institute (ANSI).
These authorities provide minimum performance criteria for various materials and products.Reference specifications are generally short,because only the standard must be stated,and they are fairly easy to write.Chances for error are minimal,as industry standards and generally recognized methods of building are being used.However, the designer must be completely familiar with and updated on the standard and how to write the appropriate specification.Sometimes the standard includedes more provisions than are needed for a particular project.
Performance
Performance specifications describe the expacted performance of the item(s) being specified.This type of specification is also considered open,as no trade names are included.Any item that meets the performance criteria can be used in the project.The means by which the required results are met is not specified,but left up to the contractor,subcontractor,or vendor.Performance specifications are often used for custom components when the designer wants to achieve a particular result that is not already manufactured.This type of specification can be more difficult to write,because the designer must know all the criteria expected as well as methods for testing (if required).Also,there is a risk that the designer could lose his or her original design concept along with control over the products used if it not carefully written.
Organization of Specifications
The organization of written specifications has been standardized in accordance with the building trades.Many architects and interior-designers use the specification system This system standardizes the format and numbering of project information used in specifications and cost estimating,and organizes the job book or project manual.The masterformat model,as shown in Table 5-2,contain 16 divisions that are based on major categories of work.Each of these major divisions is coded with a five-digit number,such as 09300 for tile.Each division,known as a broadscope,is then subdivided into narrowscope categories.The first two digits represent the broadscope,the last three digits detail the narrowscope subdivision.For example ,under painting,09900 is a brodescope category that includes several different types of painting.The level of information the designer uses depends on the complexlty of the job and specifications.
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