Search This Blog

Tuesday, July 17, 2012

The Significance of Gross Building Area

***Please see my latest book, The Science of City Design: Architectural Algorithms for City Planning and Design Leadership, on in both e-book and paperback versions.***

Gross building area is a function of the land available and the height permitted. Its mass combines with parking and pavement to produce a level of intensity. Intensity is determined by the percentage of project open space off-setting building mass and pavement area. The efficiency of a gross building area plan determines the population and activity that can be sheltered. When total gross building area is contained within sustainable geographic limits, the inventory will become a shelter resource and part of a symbiotic relationship we establish to protect our source of life. Building intensity within these limits, and occupant intensity within each building, will determine the quality of life provided.

The word “symbiotic” has several meanings. “Mutual benefit” is the definition that relates to all of my essays. A symbiotic parasite has a relationship of mutual benefit with a host that contributes to its continued survival. Our relationship to the planet must become symbiotic to survive.

My work has been devoted to a vocabulary of architectural intensity that can be measured and evaluated at existing locations. It includes forecasting software based on templates that accept vocabulary values and predict gross building area options with embedded equations. Option implications can then be evaluated based on original intensity research. Evaluation is needed because excessive intensity can be prompted by growing populations and is a threat to their quality of life. In other words, excessive intensity may protect our source of life but prolong a miserable quality of life that benefits a few.

“Gross building area” is a fundamental prediction or measurement that contributes to the definition of development capacity, or it is a given that begins a search for land with adequate capacity. It is a key measurement, forecast, or stipulation that permits the evaluation of additional implications.

“Building capacity” is the gross building area that can be constructed under the conditions noted in a design specification. Building intensity BINT is a gross building area option divided by the project open space present, planned, or provided. Development intensity DINT is the sum of a gross building area and pavement option divided by the project open space present, planned, or provided. This will be discussed in greater detail in a moment, but it should be clear that gross building area is a significant element in both equations.

The point is that gross building area is shelter capacity. Intensity defines how it is introduced. It is not a substitute for fine art. It is simply a foundation with leadership potential, and it can be a cornerstone of credibility to help us pursue architecture and city design in the public and private interest.

I have suggested in earlier essays that the goal is to supplement land use allocation with intensity awareness to protect our quality and source of life. This means that we must be able to define and predict the intensity implications of architectural design specification decisions. It is why I have focused on a language and vocabulary of intensity for use in development capacity forecasting and evaluation.

The key to intensity prediction involves accurate gross building area forecasting.  It also involves internal floor plan arrangement that will be discussed under the heading “Building Efficiency”. Shelter activity and intensity combines with the Movement, Open Space and Life Support divisions of our built environment to determine the physical, social, psychological and economic quality of life offered. A new level of instinctive awareness is telling many that it must be contained within sustainable geographic limits to protect its source of life.

We have not been able to measure or predict intensity in a language that has leadership potential. It is a function of gross building area, however; and gross building area options can be forecast from design specification values. This means we can measure and predict the intensity spectrum produced by specification combinations and evaluate their implications.

This essay proposes two intensity scales. One measures building intensity and the other, total development intensity. The equation for building intensity is BINT = GBA / (BLA * S), but I have mentioned in previous essays that GBA / BLA is a version of the floor area ratio FAR. It substitutes buildable land area BLA for gross land area GLA, however; since the two are not always equal in area and intensity is imposed on a population within the buildable land area occupied, in my opinion. When FAR is equal to GBA / BLA therefore; the definition of building intensity can be simplified to:


This is a measurement equation that ignores the amount of parking and pavement introduced. Total development area TDA includes gross building area GBA, parking area PCA, and miscellaneous pavement area MPA since they all contribute to intensity. This would make the floor area ratio FAR a development area ratio DAR equal to GBA+PCA+MPA. When DAR is substituted for FAR in the preceding equation, the equation for development intensity becomes:


These two measurements indicate the intensity of gross building area planned, present or proposed. I’ve referred to them as blood pressure readings without a frame of reference.

Measurement makes it possible to evaluate existing conditions and establish a quality of life index for intensity, but quality of life options depend on the ability to comprehensively forecast gross building area alternatives. This has been, and often still is, a trial and error effort that produces a limited number of options for evaluation within a reasonable time frame.

I created Development Capacity Evaluation software DCE to quickly forecast an infinite number of gross building area GBA options based on the design specification values entered in one of its design category templates. This unlocks the ability to calculate the intensity created by each GBA and total development area TDA option forecast. It also unlocks our ability to evaluate activity and shelter intensity options within symbiotic geographic limits.

Table 1 is included at the end of this essay to illustrate the calculation of building intensity BINT and development intensity DINT when a gross building area objective is given and the buildable land area is to be found. Project open space percentages vary in the left hand column of the Planning Forecast table to create options.

Table 2 is included to illustrate the calculation of BINT and DINT when a gross land area is given and gross building area options GBA are to be found. The number of floors varies in the left hand column of the Planning Forecast table to create options.

Please note that the DINT values are significantly greater than the BINT values. DINT values indicate the total intensity present, planned, or predicted for an urban fabric that must rely on its weave of open space for relief.

Gross Building Area Efficiency

Gross building area, pavement and project open space combine to exert varying degrees of intensity on a surrounding area. Projects combine to form neighborhoods, districts, cities and regions that are collectively referred to as urban form, but open space is often in short supply. Urban form has now grown into sprawl seeking relief from intensity and has little concern for the source of life being consumed and polluted.

The external relationship of shelter to its neighbors and environment is only part of the problem, however. When populations are considered, the internal efficiency of gross building area becomes a significant architectural issue, since population capacity and activity affects cost, return on investment, public revenue and expense, traffic generation and so on is involved.

Gross building area is a raw material that can be adapted to serve any land use category, but building efficiency BEF determines the floor area available to serve a specific activity and population. If a building is 85% efficient, 15% is devoted to wall thickness, vertical and horizontal circulation, mechanical / electrical rooms and shafts, lobbies, rest rooms and so on. I’ve called these support areas. In other words, net area is a fraction of the gross building area and the percentage indicates the first category of floor plan efficiency. Net efficiency can refer to either lease area or occupied area, however. Lease area can include all building support areas except exterior wall thickness. It is of primary interest to a landlord, since a pro-rated share of support area is leased to every tenant. The definition of lease area is contained in the leasing terms of a contract, however, and there is no consistent definition to my knowledge.

Actual building efficiency is net area that excludes all shared building support functions and areas. In other words, net building efficiency indicates the realistic area for occupation. Occupant efficiency indicates the realistic area available for personal activity. It is found by subtracting such things as, but not limited to, private reception areas, hallways, utility closets, private rest rooms, partition thicknesses, and columns from the net building area. Occupant efficiency OEF can be substantially less than  building efficiency BEF. In fact, if you subject one of your plans to net and occupant efficiency measurements the results may surprise you. Occupant efficiency can be less than 50% of gross building area GBA for some activities. This is important because the objective is to shelter shared and personal population activity without excessive intensity within a limited occupant area.

Tables 1 and 2 are concerned with gross building area GBA calculations and do not include building efficiency percentages. They are included to illustrate BINT and DINT calculations. Table 3 is based on forecast model RG1L and pertains to residential apartment buildings using grade parking around, but not under, the building(s). It includes a building efficiency percentage (Be) in its design specification template because it is a critical factor contributing to the number of dwelling units that can be included within the gross building area GBA. The percentage entered is the estimated net building area NBA that will remain.

When an apartment building efficiency percentage is multiplied by a gross building area measurement or forecast, the result defines the gross dwelling unit area remaining within the building. This is subdivided into individual unit areas designated by the number of bedrooms provided. A “mix” refers to the percentage of each unit type provided.

The Dwelling Unit Mix template in Table 3 calculates an aggregate average dwelling unit area AGG from the building efficiency, mix and net dwelling unit areas under consideration. The AGG value is used to forecast the number of dwelling units that can be included within the gross building area. The template begins with a column of potential dwelling unit types. The desired gross dwelling unit area GDA for each dwelling unit type is located in the adjacent column. A comprehensive dwelling unit area CDA is found by adding a pro-rated portion of the building support area BSA. In the case of Table 3, CDA = GDA / 85%. The MIX column identifies the percentage of each dwelling unity type being considered. In this case, the mix is 30% one bedroom dwelling units and 70% two bedroom dwelling units. When the MIX percentage is multiplied by the comprehensive dwelling unit value CDA, a pro-rated dwelling unit area PDA is found. The sum of these pro-rated areas is equal to an aggregate average dwelling unit area AGG. This is a value equal to the gross building area divided by the number of dwelling units provided. 

When a gross building area is forecast from design specification values and divided by a calculated AGG value, the result is a prediction of dwelling unit capacity. This is the number of dwelling units NDU that can be accommodated given the dwelling unit mix under consideration. Occupant space within a gross dwelling unit area is further reduced by the wall thicknesses of the floor plan.

The point is that everything begins with a forecast of gross building area potential in relation to the buildable land area BLA available, and this is a function of design specification values. The result is building mass that imposes a level of intensity on its neighbors and a gross building area that is further subdivided into net building area NBA and occupant area OCA. These areas are a function of floor plan design efficiency. When they are divided by the population POP introduced, a level of internal intensity is measured. This can be expressed as:

IINT = NBA / POP, or


From my limited experience, net building area can be 70% - 90% of gross building area and occupant area can be 70% - 90% of net building area. This means that 49% - 81% of gross building area becomes focused activity area. When population is added to net or focused activity area, internal intensity is created.

The implications become more significant when a limited, sustainable land area is considered. The development capacity of a limited land area is determined by the relationship of building height, mass, and pavement to project open space. Since buildings are not particularly efficient in general, but absolutely essential elements of survival, intensity will become a challenging issue for growing populations that seek to live within sustainable geographic limits.


If the goal is to live within sustainable limits, efficiency begins with the land use allocation of activity and gross building area within these limits. The combination of activity and intensity not only represents shelter capacity and profit but revenue and expense to both public and private interests. We are all too familiar with the results produced when activity and intensity relationships cannot support themselves over time within jurisdictional boundaries. Blight is the name of miscalculation. This takes on an added dimension of concern when environmental boundaries are considered.

The goal is to shelter the activities of growing populations without threatening their source of life with sprawl, or their quality of life with excessive intensity. This is only part of the problem, however. In the end, architectural form must represent symbiotic function within sustainable geographic limits.


It has become traditional to measure intensity with density and floor area ratios, but neither has been part of an accurate tool set. This is why I submitted new intensity equations in “Replacing Density” and “Replacing the Floor Area Ratio”. (They are part of a predictive series of equations embedded in the forecast models of Development Capacity Evaluation v2 software. The software is attached to its companion book / manual entitled, Land Development Calculations, 2e, McGraw-Hill, 2009.)

No comments:

Post a Comment