The way we work must evolve to respond to the increasing technical demands of the building industry. In addition to commodity, function, solidity, and beauty, a designer must now consider environmental stewardship, the management of complex data, and the realities of project delivery.

The evolution of sustainability through parametric modeling.

The Vitruvian qualities of firmitas, utilitas, and venustas have served as unchanging benchmarks of successful architecture for centuries. Curiously, much of the fundamental design processes of today have remained unchanged as well. However, as energy prices continue to increase and the world around us becomes ever more environmentally conscious, the demand for low-energy buildings has risen significantly. With this shift comes an entirely new set of building practices and considerations, as these sustainable buildings entail a higher complexity of design requirements. 

The way we work must evolve to respond to the increasing technical demands of the building industry. In addition to commodity, function, solidity, and beauty, a designer must now consider environmental stewardship, the management of complex data, and the realities of project delivery. 

In response to these increasingly complex factors, architects have incorporated parametric modeling into their workflow with techniques borrowed from the computer science industry. Focused on automation, this new set of tools has given the designer more freedom to create architecture despite a progressively dense framework of constraints. 

This article will explore how architects are using these tools to enhance our design process while making buildings more efficient and their occupants more productive and comfortable.

Introduction to parametric modeling and potential benefits    

In the last few years, the evolution of architectural design has seen a massive boost, as designers are relying more on the capabilities of software to resolve complex geometrical riddles and come up with unprecedented scenarios and analysis.

In many ways parametric design is a game changer in the same way that structural calculation was a stepping change to the Renaissance, when it enabled designers to foresee the consequences of more complex shapes (Brunelleschi’s dome in Florence and its complex structure of traction chains was the first one to span a larger diameter than the Pantheon in Rome, built 2000 years earlier). Building information modeling is an example of this approach, where the design is built in a virtual environment. For the first time in architectural history buildings are completely developed and finished before going on site.

Parametric design as an approach to architecture relies on establishing relationships between elements, in such a way that will allow for changes to percolate through the different elements of the design and update dynamically whenever modified. For example if you establish that a wall starts at ground level and will reach the upper slab, and a window is hosted by the wall, any change to the parent element will affect the attached element.

Designing in a parametric environment is a major change in the required approach: it’s all about finding the relationships and locking the elements together. When the designer discovers this, he or she can use it to the extreme of working purely on the relationships leaving the starting point blank, and then swapping the underlying rig to a variety of scenarios to test options, extremely different in form yet all of them following the same principles and concepts. Iterating options will never be the same, as from now on they will be partially automated by the use of smart software.

At its most basic level, coding used in computer programming is applied to the software platforms architects already use. All the functionality of the modeling software can be represented as code. Relationships are established between geometry and functions by the user, essentially automating that task for future instances. 

A standard script, for instance, could be written to measure the area of a window in a model of a building. Based on standard formulas built into the script, the geometry for a properly sized exterior shading device will be generated automatically. If the user changes the size of the window, the script automatically resizes the shading device. If the user selects twenty windows at different orientations, the script can generate shading devices to fit each condition based on the same rules. 

Establishing relationships between elements is the major difference between the old and new design process — geometric modeling evolves into parametric modeling. In geometric modeling, a shading device would be sized for a certain condition and its geometry would be created explicitly, i.e. the user would draw it directly. 

Using parametric tools, the user creates a set of rules and relationships, and the geometry is created implicitly, by the software itself. In this example, parametric modeling is used to automate a simple task that is possible with other tools, but it manages complexity of tracking individual instances. In certain ways, Revit has been doing this for years. Materials, areas, unique panels, etc. can all be managed with live feedback in kind. When geometry is changed, the information is updated. 

Currently the tool uses parameters to create geometric relationships that are otherwise not possible. Although complex forms can be drawn in the conventional design process, it is often not practical to fabricate and construct such forms without a parametric model. The data is used in two ways. First, the panelization of a curvilinear form is determined based on panel size and the number of unique panels can be established.

The model can then be tweaked by the software to minimize unique panels, while holding the overall form of the object. The second phase is fabrication. Data can be pulled from the script that defines the shape of the panel, not with drawings, but with mathematical equations. This code can be used by digital fabrication — laser cutting, cnc milling, and 3-D printing, to create the exact shape from the model.            

The future evolution of this process borrows the computer science concept of evolutionary programming or fitness algorithms. The user sets up a set of rules and goals, and the computer tests an unlimited number of scenarios until the ideal solution is found. This concept is particularly exciting for the design of high performance buildings. For instance, in addition to using a script to determine proper shading for a window, the location of the window and its glass performance properties can be tested through thousands of possible values. An energy simulation can be run automatically for each instance and the results will be tracked. In this way, the optimum configuration can be determined to a level of refinement that is not currently possible.

HOK implementation

The transition to parametric modeling in most HOK offices has already occurred with the popularity of Revit. Using intelligent geometry that can be altered through values rather than rebuilding, using live tracking of statistics, and sharing one central data file with other trades is the foundation of parametric design. The next level involves a focused effort on creating scripts within an open source community. Jeff Sanner has led the transition to parametric modeling in our Chicago office. At HOK this strategy dovetails with BIM and Building Smart initiatives that involve the entire design professional community of architects, engineers and builders. A firm-wide parametric design committee shares and transfers the firm’s project management knowledge base while training the design studios in best practices. Working with architects and engineers, designated PM specialists in each office focus on testing the latest PM software to drive the design process forward. 

William Lopez Campo of our London office has implemented parametric design in various formats throughout the past several years with a focus on transforming the adoption of Revit as the firm’s standard production tool into a portable platform developing workflows to integrate other tools into the design process.

Campo’s next step parametric design mission includes developing processes to empower designers with the capacity to explicitly trace the path from A to Z in a way that a computer can follow, and by doing this improve one or more aspects of the design: from avoiding repetitive tasks, to enabling the output of the design to react to external variables, or generating options to a theme, and potentially to the development of tools that will explore areas of artificial intelligence and evolutionary approaches to optimize the design output.

Arnold Lee, of our Los Angeles and San Francisco offices, adds that scripting or programming custom tools enables us to take advantage of powerful computing power to resolve simple problems or enhance the complexity of the output. Examples of this approach are the use of scripts to generate modules for a facade, complex analysis of solar radiation to optimize orientation of a building mass, or the approximation of a building shape for the gross area to be within a half square foot of the requested target. These processes could be achieved manually, but once the principle is established it can be trusted to a program that will resolve it more accurately and in a fraction of the time.

Specific examples

Chicago — Facade optimization for daylight and energy

A large-scale mixed use development in Moscow served as an opportunity to develop a pair of office towers optimized for the city’s cold climate. Parametric modeling was employed to develop a facade that would maximize the amount of natural light available for office occupants while maintaining thermal comfort. HOK’s Jeff Sanner, along with the studio design team and Atelier Ten of New York City, collected climate site data and ran energy analyses to establish the ideal ratio of vision glass to heavily insulated solid wall. The result was that the building would use the minimum amount of energy if the envelope had a window to wall ratio of forty percent.

However, an analysis of solar access that factored in shadows cast from surrounding buildings showed that an evenly distributed percentage of glass would leave the lower levels considerably less naturally lit than the upper levels. Sanner and the studio team then employed parametric modeling to create a system of relationships to tailor the buildings facades to their individual light conditions. 

The grasshopper plug-in for Rhino was used to map the facade with a series of punched windows whose area met the energy goal. A system was set up to increase the area of glass at the base of the facade while reducing the glass at the top of the facade. Rules were established within the script for maximum and minimum window sizes. The design could be tailored by moving an on screen slider to adjust the balance of the glass. The script gave live feedback for the total vision glass area, so as the look of the gradient was tuned by the architect, the framework would ensure the energy balance was maintained. 

The script was then tuned to assist in the constructability of the facade. The original product has a smooth gradient of glass sizes, whereby each piece of glass was a slightly different size. To minimize the number of unique panels, Sanner altered the script to control the number of unique panels. The variants are then moved down from thousands to dozens of unique panels. The facade design adjusts in real time, and can be further adjusted to meet the owner’s budget and aesthetic requirements.  

Daylighting analysis was used to confirm that access to daylight improved significantly in the lower levels, while the reduced glass at higher levels actually helped reduce glare.

Los Angeles — ARTIC — Managing construction of complex panels

The intermodal high speed rail station in Anaheim known as ARTIC was also realized using parametric design. The project is a large open public space in the tradition of long-span rail vaults and stations, re-imagined as a diaphanous light web of structure and enclosure, a diagrid shell. Arnold Lee and the HOK/Parsons Brinkerhoff design team used a non-uniform geometry to open up the shell towards the public facade and northern light, and close and shield the southern facade. The resulting design emphasizes efficient energy performance, integrated engineering analysis, and provides documents to builders to price and provide feedback.

The design process started with Rhino 3D, Autocad, and 3DStudioMax developing a shell system spanning the program elements and various modes of transportation. The models were then optimized in Digital Project. The precise geometry and spans were designed and coordinated using specific ETFE pillow panel design software in the DP environment. Grasshopper 3D scripting allowed the team to analyze and determine the best shapes for complex curvature panel surfaces, rationalizing into repetitive and manageable systems reducing cost and allowing for fabrication.

Once the entire model was built, energy performance was analyzed and natural ventilation and shading information allowed us to change the diagonal spacing and overhangs as well as the density and performance of the glass and ETFE panels. 

Finally, the documents and complex mathematical shapes were pulled from the model and described in drawings and work-point spreadsheets. The engineers, vendors and fabricators were able to provide HOK with detailed feedback that allowed the team to modify the design to work for the widest array of bidders. The relative ease of managing so much detailed, complex digital information allowed the team to integrate rivers of engineering data, and to give real, living depth and development to what ten years ago would have been simple a geometric model study.

London — Conceptual design test fits with enhanced speed

HOK’s William Lopez Campo concurs that an important aspect of computational design is the ability to generate several options and compare them to understand the impact on specific aspects of the building performance. In 2007, an early approach to scripting aimed at sustainable performance assessment was used to analyze the analysis of thermal gain performance of an ensemble of 3 towers of irregular shape, the Flame Towers in Baku, Azerbaijan. By comparing the combined performance of all three towers when changing the angle of the towers the design team optimized the relative position and orientation of the prevailing flat side. It was an important milestone in understanding the capabilities of the software, and reinforced our corporate belief in the need to incorporate sustainability as early as possible in the design, ideally before design begins, as with the Moscow example.


The design of high-performance buildings through advanced computational analysis has become standard operation for leading design offices. As the intersection of design, engineering, and budget becomes more complex and drives projects to be higher performing and lower cost, parametric design tools permit elegant new design solutions that meet and exceed our client’s needs. We now have the digital tools to keep pace with the technological demands in building design. 

The impact of parametric modeling has enhanced the design process and improved building efficiency; it is the paradigm shift of the traditional tenets of architecture; tenets that have always included the choreography of design and art. Parametric modeling adds science to the equation, advancing design and sustainability and adds a third tenet to the successful design of architecture.