5.1 The payback method is part of a family of economic evaluation methods that provide measures of economic performance of an investment. Included in this family of evaluation methods are life-cycle costing, benefit-to-cost and savings-to-investment ratios, net benefits, and internal rates of return.5.2 The payback method accounts for all monetary values associated with an investment up to the time at which cumulative net benefits, discounted to present value, just pay off initial investment costs.5.3 Use the method to find if a project recovers its investment cost and other accrued costs within its service life or within a specified maximum acceptable payback period (MAPP) less than its service life. It is important to note that the decision to use the payback method should be made with care. (See Section 11 on Limitations.)1.1 This practice provides a recommended procedure for calculating and applying the payback method in evaluating building designs and building systems.1.2 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

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5.1 The AHP method allows you to generate a single measure of desirability for project/product/process alternatives with respect to multiple attributes (qualitative and quantitative). By contrast, life-cycle cost (Practice E917), net savings (Practice E1074), savings-to-investment ratio (Practice E964), internal rate-of-return (Practice E1057), and payback (Practice E1121) methods all require you to put a monetary value on benefits and costs in order to include them in a measure of project/product/process worth.5.2 Use AHP to evaluate a finite and generally small set of discrete and predetermined options or alternatives. Specific AHP applications are ranking and choosing among alternatives. For example, rank alternative building locations with AHP to see how they measure up to one another, or use AHP to choose among building materials to see which is best for your application.5.3 Use AHP if no single alternative exhibits the most preferred available value or performance for all attributes. This is often the result of an underlying trade-off relationship among attributes. An example is the trade-off between low desired energy costs and large glass window areas (which may raise heating and cooling costs while lowering lighting costs).5.4 Use AHP to evaluate alternatives whose attributes are not all measurable in the same units. Also use AHP when performance relative to some or all of the attributes is impractical, impossible, or too costly to measure. For example, while life-cycle costs are directly measured in monetary units, the number and size of offices are measured in other units, and the public image of a building may not be practically measurable in any unit. To help you choose among candidate buildings with these diverse attributes, use AHP to evaluate your alternatives.5.5 The AHP method is well-suited for application to a variety of sustainability-related topics. Guide E2432 states when applying the concept of sustainability, it is necessary to assess and balance three dissimilar yet interrelated general principles—environment, economic, and social—based on the best information available at the time the decision is made. Use AHP for pairwise comparisons among environmental attributes, among economic attributes, and among social attributes, and for establishing relative importance weights for each attribute and for each of the three general principles to which the attributes are attached. Use the AHP-established relative importance weights to select the preferred project/product/process from among the competing alternatives.5.6 Potential users of AHP include architects, developers, owners, or lessors of buildings, real estate professionals (commercial and residential), facility managers, building material manufacturers, equipment manufacturers, product and process engineers, life cycle assessment experts, and agencies managing building portfolios.1.1 This practice presents a procedure for calculating and interpreting AHP scores of a project’s/product’s/process’ total overall desirability when making capital investment decisions.3 Projects include design, construction, operation, and disposal of commercial and residential buildings and other engineered structures.4 Products include materials, components, systems, and equipment.5 Processes include procurement, materials management, work flow, fabrication and assembly, quality control, and services.1.2 In addition to monetary benefits and costs, the procedure allows for the consideration of characteristics or attributes which decision makers regard as important, but which are not readily expressed in monetary terms. Examples of such attributes that pertain to the selection among project/product/process alternatives are: a construction projects’s building alternatives whose nonmonetary attributes are location/accessibility, site security, maintainability, quality of the sound and visual environment, and image to the public and occupants; building products based on their economic and environmental performance; and sustainability-related issues for key construction processes that address environmental needs, while considering project safety, cost, and schedule.1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.1.4 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

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4.1 Standard practices for measuring the economic performance of investments in buildings and building systems have been published by ASTM. A computer program that produces economic measures consistent with these practices is available.4 Discount Factor Tables has been published by ASTM to facilitate computing measures of performance for most of the practices.4.2 This guide can be used to: (1) identify types of building design and system decisions that require economic analysis; (2) match the technically appropriate economic methods with the decisions; and (3) locate the methods in the ASTM practices and adjuncts listed in Section 2.4.3 More than one method can be technically appropriate for many building decisions. Therefore the choice in practice of which technically appropriate economic method to use for evaluating a particular building decision will often depend on the perspective of the user. Some examples of factors that influence the user are: (1) ease of applying the methods, (2) level of familiarity of the user with the methods, (3) preference of the user for different methods, and (4) presence of budget limitations for the projects.4.4 This guide identifies some features and limitations of the methods that might influence users' choices under varying conditions.1.1 This guide identifies types of building design and building system decisions that require economic analysis and recommends ASTM practices, adjuncts, and computer programs that may be used to implement the appropriate economic methods for each decision type.1.2 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

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5.1 The IRR method has been used traditionally in finance and economics to measure the percentage yield on investment.5.1.1 The IRR method is appropriate in most cases for evaluating whether a given building or building system will be economically efficient, that is, whether its time-adjusted benefits will exceed its time-adjusted costs over the period of concern to the decision-maker. However, it has deficiencies that limit its usefulness in choosing among projects competing for a limited budget.5.2 The AIRR method is a measure of the overall rate of return that an investor can expect from an investment over a designated study period. It is appropriate both for evaluating whether a given building or building system will be economically efficient and for choosing among alternatives competing for a limited budget.5.2.1 The AIRR method overcomes some, but not all, of the deficiencies of the IRR. The AIRR is particularly recommended over the IRR for allocating limited funding among competing projects.1.1 This practice covers a procedure for calculating and interpreting the internal rate of return (IRR) and adjusted internal rate of return (AIRR) measures in the evaluation of building designs, systems, and equipment.1.2 The values stated in inch-pound units are to be regarded as standard. The values given in parentheses are mathematical conversions to SI units that are provided for information only and are not considered standard.1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.1.4 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

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5.1 The NB (NS) method provides a measure of the economic performance of an investment, taking into account all relevant monetary values associated with that investment over the investor’s study period. The NB (NS) measure can be expressed in either present value or equivalent annual value terms, taking into account the time value of money.5.2 The NB (NS) method is used to decide if a given project is cost effective and which size or design for a given purpose is most cost effective when no budget constraint exists.5.3 The NB (NS) method can also be used to determine the most cost effective combination of projects for a limited budget; that is, the combination of projects having the greatest aggregate NB (NS) and fitting within the budget constraint.5.4 Use the NB method when the focus is on the benefits rather than project costs.5.5 Use the NS method when the focus in on project savings (that is, reductions in project costs).1.1 This practice covers a recommended procedure for calculating and interpreting the net benefits (NB) and net savings (NS) methods in the evaluation of building designs and systems.1.2 The values stated in inch-pound units are to be regarded as standard. The values given in parentheses are mathematical conversions to SI units that are provided for information only and are not considered standard.1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.1.4 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

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