The ANSI/BOMA Z65.4 measurement method for multi-unit residential buildings.
The ANSI/BOMA Z65.4-2010 standard provides direction for the measurement of multi-unit residential buildings with four or more units. This article explains the standard, how it is applied in measuring area, and the unique differences between this standard and other measurement methods. Application of this standard provides a flexible, useful, and consistent measuring method for its users. Moreover, use of the ANSI/BOMA Z65.4-2010 standard reduces confusion by adhering to an industry standard. A potential effect of its use may be the reduction of mismeasurement claims against real estate professionals.
Measurement errors are a common reason for lawsuits involving appraisers and brokers. Based on its claims statistics, LIA Administrators & Insurance Services reports that alleged mis-measurement is a problem of "frequency" for residential appraisers--meaning the problem occurs in many claims against residential appraisers--and it is a problem of "severity" for commercial appraisers--meaning the problem results in large damages claims. How can there be so much conflict regarding something that appears as straightforward as measuring a home or a building? Some key reasons for measurement discrepancies include the lack of standardization and gaps in knowledge. Regardless of the reasons, measurement errors can cause trouble for appraisers.
The Building Owners and Managers Association International (BOMA), in collaboration with the Institute of Real Estate Management, National Association of Home Builders, and National Multi Housing Council, has developed a standard for measuring the area of residential multi-unit buildings. This standard was certified by the American National Standard Institute (ANSI) in 2010 and became BOMA's Multi-Unit Residential Buildings: Standard Methods of Measurement (ANSI/BOMA Z65.4-2010).
The ANSI/BOMA Z65.4 standard is a voluntary guideline for describing, measuring, calculating, and reporting area for multifamily residential homes. The standard is flexible and provides several methods for measuring and reporting area.
The actual level of detail in measurement is dependent on an assignment's scope of work; one or more of the methods in ANSI/BOMA Z65.4 may be used. An appraiser may select the methodology that is most applicable to an assignment and document the approach in the report. Documenting the methodology provides the report reader with sufficient information to replicate the measurements and results.
ANSI/BOMA Z65.4 is applicable for attached multifamily homes with four or more units. It is not meant for commercial properties, mixed-use buildings, attached duplexes or triplexes, detached single-family residential homes, or detached townhomes. (1)
Most appraisers are familiar with Fannie Mae's guidance on measuring attached residential units, such as condos or townhomes, which suggests measuring area from interior finished wall to interior finished wall. (2) Often the Fannie Mae method produces different measurements than those in the property's description in the local multiple-listing service. Why is that? Typically, the discrepancy is because different real estate professionals (assessors, architects, contractors, and realtors) use different methods for measuring, calculating, and reporting the area. Also, local markets may adhere to differing measurement methodologies due to custom, statutes, or regulations. Because of these inconsistencies, it is important that appraisers clearly identify and define the measurement criteria used for the subject property and consistently apply the same measurement protocol to comparable properties. (3)
The ANSI/BOMA Z65.4 standard provides a uniform protocol for measuring, calculating, and reporting area. It is unique as the only standard that specifically addresses multi-unit residential property, has a buy-in from many stakeholders, and has been peer reviewed. Moreover, this measurement standard has three key features that some ad-hoc methods do not: flexibility, usefulness, consistency.
The first feature is flexibility. This standard allows users to select from one of two measuring methods: either the gross method, which the standard also calls "Method A," or the net method, which the standard also calls "Method B." The standard allows measurement, calculations, and reporting of individual units or aggregate areas of a building or both. Users of the standard have the flexibility to select the method most applicable for an assignment.
The second feature is usefulness. This standard is useful to appraisers, architects, assessors, home inspectors, and realtors for measuring multifamily buildings. As noted, no uniform standard has previously dealt with measurement of multifamily residential homes. Appraisers had used their own judgment when measuring attached units, such as condos, and the measurement method employed depended on the appraiser. Some appraisers determined wall thickness and measured to the external side of the unit's wall. Others measured the internal walls, as described by Fannie Mae and HUD guidelines. (4) And some appraisers used a hybrid of the two approaches.
The third feature of the standard is consistency. The ANSI/BOMA Z65.4 standard creates a baseline for measuring and communicating area. It provides uniform rules for measuring and reporting area. The use of a consistent, peer-reviewed standard reduces confusion and provides transparency, which in turn may reduce the possibility of litigation.
ANSI/BOMA Z65.4 Overview
There are two sections to the ANSI/BOMA Z65.4-2010 standard. One section provides the key definitions used within the standard, while the other section discusses application of the standard in detail. In the application portion of the standard, you will find details on two different methods for measurement and the specific steps required for measurement, calculation, and reporting under the standard. Each measurement method entails four steps; these steps will be discussed later in this article.
There are some unique differences between the ANSI/BOMA Z65.4 standard and other measurement methods. For example, ANSI/BOMA Z65.4 requires the user to explicitly state which method is used to calculate area (the gross measurement method or the net measurement method). Unlike the measurement standard for single-family homes (ANSI Z765-2013), this standard does not specify units of measurement or the precision of units measured. (5) Also, ANSI/BOMA Z65.4 does not distinguish between finished and unfinished areas, or above-and below-grade areas. The standard addresses measurement of floor area only and does not address volume measurements. In a mixed-use building, the standard only applies to the area with residential occupancy. One important caveat to ANSI/BOMA Z65.4 states,
Users of this standard are advised to consult with competent legal counsel prior to applying this standard or choosing a method herein. It is not intended to supersede or supplant state or local statutes governing the measurement of multi-unit residential buildings or the living units therein. (page 3)
ANSI/BOMA Z65.4-2010 defines key terms that are crucial to the correct application of the measurement methodology. Appraisers should become familiar with the standard-specific definitions because they may differ from those in other measurement guides or in The Dictionary of Real Estate Appraisal, sixth edition. Some important ANSI/BOMA Z65.4 definitions related to measurement of areas are summarized below. (6)
Building perimeter. A horizontal line forming a perimeter that encompasses all the construction elements, both enclosed and unenclosed, of a given floor of a building.... The building perimeter is drawn at the exterior edge of [all constructed] elements.
Centerline. A line that is equidistant from the finished surfaces of a wall.
Common area. Areas within the construction gross area of a multi-unit residential building that are designated for use by two or more occupants of living units in the building and/or that serve two or more of the living units.
Construction gross area. The total of all the horizontal floor areas (as viewed on a floor plan) of all floors of a building contained within their building perimeters excluding voids.
Demising wall. A wall between two adjacent units, restricted headroom areas or limited common areas.
Finished surface. The face of a wall or window wall that is provided as part of the base building for the general use of occupants. [Excludes special surfacing materials or furred out space for plumbing, conduit, etc.]
Limited common area. Areas that are within the construction gross area of a multi-unit residential building but are outside the measure line and designated for sole use by the adjacent occupant of a specific living unit. [For example, private balconies, decks, patios, porches, or terraces.]
Living unit. A portion of the construction gross area of a building used exclusively by the occupant for residential purposes, exclusive of limited common area and restricted headroom area.
Major vertical penetration. A floor opening in excess of 1 square foot (or 0.1 square meter) that serves vertical building systems or vertical circulation functions. [For example, stairs, elevator shafts, ventilation ducts.]
Multi-unit residential building. A building with four or more living units plus ancillary areas such as building lobbies, corridors, stairs, lounges, ... intended primarily for the use of the occupants of living units in the building.
Restricted headroom. Space within a living unit that does not meet the [minimum ceiling height] requirement of the International Building Code section 1208.2.
Storage unit. A fully enclosed area that may be unfinished, have restricted headroom or limited building services but is suitable for storage. [Excludes areas contiguous to a living unit.]
Structured parking. Enclosed, structured floor area used for transient storage of motor vehicles. [Excludes off-street uncovered parking, on-grade parking below an elevated building, and carports.]
Unit gross area. The area of a unit generally bounded by the centerline of demising walls that separate a unit from adjacent units, the measure line of adjacent exterior enclosures, the finished surface of the unit side of walls that separate a unit from an adjacent major vertical penetration, and the finished surface of the common element side of a wall between the unit and an adjacent common area. [Unit gross area excludes limited common areas and restricted headroom area.]
Unit net area. The area of a unit that is bounded by the inside finished surface of the perimeter walls of that unit.
Void. An absence of a floor where a floor might otherwise be expected or measured.
Area Measurement and Calculation
As mentioned, ANSI/BOMA Z65.4 provides some flexibility for users. It offers two different methods that may be used for measurement and calculation of area: the gross method/Method A and the net method/Method B. As these names imply, the guidelines are for the measurement of unit gross area or unit net area. Keep in mind that the specific method used must be expressly stated in any report.
The standard specifies that both measurement methods follow the same four steps in the standard's application:
1. Determine the construction gross area of the building and of all its floors.
2. Separate all area by type for each floor.
3. Determine the boundaries and apply wall priority of each type of space.
4. Calculate the area for each type of area and tabulate.
Exhibit 1 shows a measurement process flow chart; each step will be explained in detail next.
Determine Construction Gross Area
The first step in multi-unit residential measurement is to determine the construction gross area. The construction gross area of each floor serves as the basis for measurement of a building. To compute the construction gross area, first the gross area for each floor is determined, and then the gross area of all floors is summed to produce a total construction gross area.
It is important to record the construction gross area for each floor and all floors. The area for each floor is determined by either direct measurement or building plans. When measuring to determine construction gross area, measurements are taken from the building perimeter. Alternatively, if measurements are taken from plans, use the external measurements listed on the blueprints.
After the construction gross area for each floor has been determined, sum the total construction gross area for all floors of the building, and record it. There should be no gaps or overlap in the measured area, but voids are omitted from the construction gross area calculations. (7)
Partition Construction Gross Area by Type
The second step in measurement is to partition the construction gross area by area type. The ANSI/BOMA Z65.4 standard identifies seven area types in buildings:
* Major vertical penetration (MVP)
* Living area (LA)
* Storage unit area (SUA)
* Restricted headroom area (RH)
* Limited common area (LCA)
* Common area (CA)
* Structured parking (SP)
Identifying building area types is straightforward based on the standard's definitions, but calculating the areas can be challenging. This is because the initial measuring point is dependent on the adjacent type of area, with the boundary or demising wall as the separator between adjacent spaces. For example, questions may arise as to whether an area is to be measured from the interior finished side (the near side), from the exterior side, either finished or unfinished (the far side), or the midpoint of the wall. Exhibit 2 illustrates the relevant points of a demising wall. (8)
Determine Boundaries and Wall Priority for Type of Space
Under the standard, the third step in measuring the multi-unit space is to determine the boundaries of each type of space and which wall surface constitutes the boundary between the two adjacent classes of space.
How the standard treats boundaries differs depending on whether gross or net area is being computed. If the unit gross area is being computed, then the boundary is the building perimeter for all areas adjacent to the perimeter of the building. However, if the unit net area is being computed, then all exterior walls at the perimeter of the building are considered common area, which is excluded from the unit net area measurement.
The standard includes matrix charts, or wall priority diagrams, to eliminate guesswork regarding where to start measuring: the near side, the far side, or the centerline. To avoid misinterpretation, the charts should not be used without reference to the complete standard.
Exhibit 3 shows the wall priority diagram for the unit gross method, and Exhibit 4 shows the wall priority diagram for the unit net method. In each matrix, the columns and rows denote each of the seven area types. The intersection point on the matrix of two area types indicates the initial measuring point. In the matrices, note that living area (LA) and storage unit area (SUA) elements are treated the same; therefore, a condensed, six-by-six matrix is used.
To illustrate, assume there is a corner unit with another unit on an adjacent wall and a major vertical penetration on another adjacent wall. If Method B (unit net area) is used to calculate the area of the end unit, then to determine the beginning point to measure for the wall adjacent to the wall of the other living area, look at the rightmost column, LA/SUA, in Exhibit 4. Then locate the row labeled LA/SUA, and follow that row to the right to the LA/SUA column. The box where the row and column intersect is marked with an asterisk (*). This is because Method B states that restricted headroom, living/storage, and limited common areas are generally separated by demising walls, which are considered common area. Therefore, the measuring point is the near side for the adjacent living units.
For the wall adjacent to the major vertical penetration, follow the same steps, starting with the column labeled MVP and locate where row LA/SUA intersects with that column; here the box indicates measurement is from the near side of the finished wall. The other walls in this example are outside corner walls and are measured from the near side of the finished wall as well (remember, in Method B exterior walls are common area). It is interesting to note that the resulting net area is the same area that results when using Fannie Mae's measurement method. Thus, Fannie Mae's method is measuring the unit's net area, which is different from the gross area measurements that appraisers typically use for other single-family residential units.
Reporting of Area
Once all of the appropriate areas are calculated, they must be tabulated and reported. Be aware that the client may want only the net measurements, only the gross measurements, or both in the valuation assignment. A summary Excel spreadsheet can be developed with the calculations segmented and reported by location (floor), individual unit, and area type. ANSI/BOMA Z65.4 includes a global summary of areas spreadsheet, illustrating tabulated areas partitioned into individual area type by floor and the summation of all floors.
Exhibit 5 shows an example of a global summary of areas analysis. Each area type is listed individually, summed by floor, and then summed by building. The spreadsheet is scalable, depending on the scope of work of the assignment. For example, if the valuation assignment is only for a single unit, the document may be modified to only report the unit of interest. Conversely, if the assignment is for a block of units in the building (a subset of all units), the global summary of areas can be modified to reflect the units of interest. Thus, the document is flexible enough to report net and/or gross areas of a multi-unit residential building.
Case Study Example
ANSI/BOMA Z65.4 includes details that cannot all be covered here, but to illustrate how the standard works in practice, a simple case study example of measurement and tabulation is shown next.
The subject property's floor plan is displayed in Exhibit 6. The property of interest is Unit A, an end unit in a multifamily, multistory residential building. The unit has a private deck, a glass-walled atrium that looks down to the floor below, and ingress/egress via a common hallway. The walls between units are two feet thick; other walls are only one foot thick. As part of an appraisal assignment, the client wants to know the construction gross area, unit gross area, unit net area, major vertical penetration area, common area, limited common area, and void area for Unit A only.
Remember from the discussion above that the first step to determining the unit gross area or unit net area is to calculate the construction gross area. Note that in Exhibit 6 the values outside of the diagram are exterior measurements, while values inside the diagram are interior measurements. The construction gross area is made up of the combined areas of the living area (LA), common area (CA), limited common area (LCA), and the major vertical penetration area (MVP). Voids are excluded from the construction gross area (CGA).
Keep in mind the CGA is technically the external perimeter of the entire floor. In this example, the client is only concerned with Unit A of the building, and the CGA is restricted to those elements adjacent to the unit.
We begin by computing the construction gross area's components as displayed in the Exhibit 6 illustration:
1. Calculate area of the living area of the left-most square. Interior dimensions 10 ft. x 10 ft.; the wall width is one foot, producing 11 ft. x 11 ft. = 121 sq. ft. LA.
2. Calculate the limited common area. Deck 9 ft. x 6 ft. = 54 sq. ft. LCA.
3. Calculate the common area. Hallway 12 ft. x 22 ft. = 264 sq. ft. CA, minus elevator 9 ft. x 9 ft. = 81 sq. ft. MVP = 183 sq. ft. CA.
4. Calculate the void area. 13 ft. x 11 ft. = 143 sq. ft.
5. Calculation total living area. 41 ft. x 22 ft. + 11 ft. x 11 ft. (from step 1) = 1,023 sq. ft. LA.
6. Calculate construction gross area of Unit A. 1,023 sq. ft. LA + 183 sq. ft. CA + 54 LCA + 81 sq. ft. MVP = 1,341 sq. ft. CGA.
At this point we have calculated most of what the client typically wants. Notice that the living area measurements are external or gross measurements. So, the living area as calculated is the same as the unit gross area. The above-calculated common area is different for the unit net area, however, since the area between the walls is considered common area. The calculation is modified as follows for the net common area:
(12 ft. x 22 ft.) + (50 ft. x 1 ft.) + (41 ft. x 1 ft.) = 355 sq. ft. - 81 MVP sq. ft. = 274 sq. ft.
Finally, the unit net area can be calculated as follows:
(40 ft. x 20 ft.) + (10 ft. x 10 ft.) = 900 sq. ft.
It is interesting to note that the net common area is greater than the gross common area. The net common area has more area because in the net model the side wall thickness is considered common area.
Now that all the components are calculated, the only remaining piece is to tabulate the areas for the report. The resulting calculations are transcribed into the area summary document that is inserted into the final report to the client. Exhibit 7 shows the final global area summary spreadsheet for the case study example.
The ANSI/BOMA Z65.4-2010 standard provides directions for the measurement of multifamily residential homes in buildings of four or more units. Application of this standard provides a flexible, useful, and consistent measuring method for its users. Moreover, adhering to a recognized industry standard of measurement may help reduce the possibility of litigation for real estate professionals.
Suggested by the Y. T. and Louise Lee Lum Library
American National Standards Institute (ANSI)
* Appraising Residential Properties, 4th edition
Building Owners and Managers Association International
* Best practices for floor measurement
* Standards list
(1.) A systematic methodology for calculating the square footage of single-family residential buildings has been developed by the National Association of Home Builders and can be found in ANSI standard Square Footage--Method for Calculating: ANSI Z765-2013. For additional discussion see, Byron Miller, "The ANSI Z765 Standard for Calculating Square Footage," The Appraisal Journal (Fall 2013): 300-307.
(2.) Fannie Mae, Selling Guide (March 29, 2016), http://bit.ly/FannieGuide.
(3.) Barrett A. Slade, The Valuation of Office Properties (Chicago: Appraisal Institute, 2009), 37.
(4.) See Handbook 4000.1, FHA Single Family Housing Policy Handbook, http://bit.ly/FHAhandbook.
(5.) For example, ANSI Z765 requires measurement to the nearest inch or tenth of a foot.
(6.) These definitions are excerpted from Section 5, "Definitions," in ANSI/BOMA Z65.4-2010. Consult the standard for the full definitions of these terms as well as additional important definitions and discussion commentary that elaborates on aspects of each item.
(7.) BOMA has a separate, specific guide for determining construction gross area, The Gross Areas of a Building: Methods of Measurement, ANSI/BOMA Z65.3-2009, available at http://bit.ly/GrossArea.
(8.) ANSI/BOMA Z65.4 includes an illustrated guide on demising wall boundaries.
By Byron Miller, SRA, AI-RRS
Byron Miller, SRA, AI-RRS, RAA, MSSE, is a certified residential appraiser in Minnesota and Wisconsin. His firm, BM Appraisals, specializes in valuation services for consulting, estate, litigation support, mortgage, and relocation. Miller has fifteen years of appraisal experience, and was previously a computer engineer. He has taught prelicensing appraisal courses and is an Al-approved instructor and developer. Miller serves on the boards of Al Holdings, REAGIT, Relocation Appraisers & Consultants, and the Twin Cities Estate Planning Council; he also serves as government relations chair for the North Star Chapter of the Appraisal Institute. Miller holds a bachelor's degree with a focus on computer science from Metropolitan State University and a master's degree in software engineering from St. Thomas University. Contact: email@example.com
Exhibit 3 Wall Priority Diagram, Method A: Unit Gross Area Living Unit Major Gross Area Vertical (LA) or Storage Penetration Unit Gross Restricted (MVP) Area (SUA) Headroom (RH) Major Vertical Center line Finished Finished Penetration (MVP) far side far side Living Unit Gross Finished Center line Finished Area (LA) or Storage near side far side Unit Gross Area (SUA) Restricted Finished Finished Center line Headroom (RH) near side near side Limited Common Finished Finished Finished Area (LCA) near side near side near side Common Area (CA) Finished Finished Finished near side near side near side Structured Finished Finished Finished Parking (SP) near side near side near side Limited Common Area Common Structured (LCA) Area (CA) Parking (SP) Major Vertical Finished Finished Finished Penetration (MVP) far side far side far side Living Unit Gross Finished Finished Finished Area (LA) or Storage far side far side far side Unit Gross Area (SUA) Restricted Finished Finished Finished Headroom (RH) far side far side far side Limited Common Center line Finished Finished Area (LCA) far side far side Common Area (CA) Finished Center line Finished near side far side Structured Finished Finished Center line Parking (SP) near side near side Reprinted with permission, Building Owners and Managers Association International, ANSI-BOMA Z65.4-2010, Multi-Unit Residential Buildings: Standard Methods of Measurement, [c] 2010. All rights reserved. Exhibit 4 Wall Priority Diagram, Method B: Unit Net Area Major Vertical Penetration Structured Common (MVP) Parking (SP) Area (CA) Major Vertical Center line Finished Finished Penetration (MVP) far side far side Structured Finished Center line Finished Parking (SP) near side far side Common Area (CA) Finished Finished Center line near side near side Limited Common Finished Finished Finished Area (LCA) near side near side near side Restricted Finished Finished Finished Headroom (RH) near side near side near side Living Unit Net Finished Finished Finished Area (LA) or near side near side near side Storage Unit Net Area (SUA) Living Unit Net Area Limited (LA) or Common Area Restricted Storage Unit (LCA) Headroom (RH) Net Area (SUA) Major Vertical Finished Finished Finished Penetration (MVP) far side far side far side Structured Finished Finished Finished Parking (SP) far side far side far side Common Area (CA) Finished Finished Finished far side far side far side Limited Common * Finished Finished Area (LCA) far side far side Restricted Finished * Finished Headroom (RH) near side far side Living Unit Net Finished Finished * Area (LA) or near side near side Storage Unit Net Area (SUA) * Area types separated by demising walls, which are common area. Reprinted with permission, Building Owners and Managers Association International, ANSI-BOMA Z65.4-2010, Multi-Unit Residential Buildings: Standard Methods of Measurement, [c] 2010. All rights reserved. Exhibit 5 Example, Global Summary of Areas Spreadsheet Major Construction Vertical Storage Unit Gross Penetration Living Unit Floor Level ID Area Area Area Area * Basement S1 200 S2 200 S3 100 200 S4 200 Floor totals 4,000 100 800 1st Floor 100 1,064 900 101 1,064 1,000 102 1,064 100 1,000 103 1,064 800 Floor totals 4,256 100 3,700 2nd Floor 200 1,064 900 201 1,064 1,000 202 1,064 100 1,000 203 1,064 800 Floor totals 4,256 100 3,700 Bldg. Total 12,512 300 11,400 800 Limited Common Restricted Common Area Structured Unit Headroom Area ([double Parking Floor Level ID Area ([dagger]) dagger]) Area Basement S1 S2 S3 100 1,000 S4 Floor totals 100 1,000 1st Floor 100 100 64 101 64 102 64 100 103 64 Floor totals 100 256 100 2nd Floor 200 100 64 201 64 202 64 100 203 64 Floor totals 100 256 100 Bldg. Total 200 512 300 1,000 Method: Gross/Method A Measurement Units: Square feet Storage areas are detached from living area. ([dagger]) Private patios, decks, porches, or balconies. ([double dagger]) Shared lobbies, hallways, plazas, patios, decks, porches, or balconies. Exhibit 7 Example, Unit A Global Area Summary Document Construction Unit Gross Area UGA UNA Floor Level ID (sq. ft.) (sq. ft.) (sq. ft.) 2nd Floor 200 1,341 1,023 900 201 xxxx xxxx XXX Floor Totals xxxx xxxx xxxx Bldg. Totals xxxx xxxx xxxx Major Vertical Limited Penetration Living Common Common Unit Area Area Area Area Floor Level ID (sq. ft.) (sq. ft.) (sq. ft.) (sq. ft.) 2nd Floor 200 64 1,023 54 183/274 * 201 XX XXXX XX xxx/xxx Floor Totals XXX xxxx xxx/xxx Bldg. Totals XXX xxxx XXX xxxx/xxxx * First value is gross; second value is net.
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|Title Annotation:||Peer-Reviewed Article|
|Date:||Mar 22, 2016|
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