FenestraPro Premium: A Generative Tool for Façade Design in ArchitectureAECbytes Review (March 16, 2017)

Back in 1995, I published a research paper entitled “GENWIN: A Generative Computer Tool for Window Design in Energy-Conscious Architecture” in the journal, Automation in Construction, based on the work I did as an M.Phil in Architecture student. The idea was to demonstrate the use of computers as active tools for design by “generating” solutions rather than simply as passive tools for evaluating designs, as they were being used at that time. The prototype tool which I developed and wrote about was focused on a very simple use case—given the desired daylighting in a room, it generated all possible window combinations in the specified wall of the room (assuming there was only one wall with windows) which could satisfy the daylighting requirements. This work was inspired by the considerable amount of research in generative design in architecture that was being conducted in academia at that time.

Given that it has been over 20 years since that paper was published and even more since the concept of generative design in architecture was introduced and researched by leading academics at top universities around the world, you would expect generative design to be ubiquitous in AEC technology by now. Not only this, we also have BIM, which makes it so much easier to develop intelligent tools by providing a building representation that can be understood and evaluated rather than needing to be inferred as we had to do with CAD.  Yet, while generative design is the subject of much talk (see, for example, the recent Autodesk University), the number of commercial generative design tools that we actually have can be counted on one hand. While Autodesk seems to be developing Project Fractal as a generative design tool for AEC, the only established tool that comes to mind is SITEOPS (now part of Bentley), which applies generative technology to site design.

This is why when I came across FenestraPro Premium as a potential generative design solution for building façades, I was intrigued and wanted to find out more. What exactly does it do and how does it work? The results of my findings are captured in this AECbytes article.

Overview of FenestraPro Premium

Any kind of analysis or evaluation tool needs to work off a semantically-rich model of the building, and this is true even for a generative design tool—after all, it has to test all the solutions it generates to find those that meet the specifications. Rather than build a modeling solution from scratch, it makes more sense for these tools to “piggy-back” on top of an existing BIM solution, and for FenestraPro Premium, that solution happens to be Revit. In fact, this is how the tool first came to my attention in 2015—as a Revit plug-in for façade design—and I wrote about it briefly in my AEC Technology Updates, Fall 2015 article. It is developed by a relatively new company based in Ireland, FenestraPro, and made available in the US and in Europe through resellers.

FenestraPro Premium falls squarely in the sustainable design category of AEC tools, with its scope extending to three main energy-related analysis categories—thermal, solar and daylighting—and how they are impacted by the façade design of a building. It may come as a surprise, but the performance of a façade can influence the energy use of a building by over 50%, taking into account heat loss, heat gain, and natural daylight. Thus, even though it’s the aesthetic quality of a façade that architects tend to focus on, the availability of dedicated tools for façade design focused on its energy performance can serve as a good counterpoint and help ensure that the performance of a proposed façade design is not compromised by its aesthetics. FenestraPro Premium works at both the conceptual and detailed stages (Figure 1), so that it can provide inputs on the façade design at the earliest stages of design as well as help to fine-tune details such as the amount and type of glazing, window and curtain wall configurations, shading devices, material selection, and so on, at later stages so that the facade continues to meet the specified performance criteria.

Figure 1. Using FenestraPro Premium with a Revit model, at both the conceptual and detailed design stages.

How It Works

As with most generative design and analysis tools, most of the heavy lifting in FenestraPro Premium takes place behind the scenes and is not visible to the user, making the tool very intuitive and easy to use. To start with, it really is an add-in to Revit rather than a plug-in, which means that it is embedded into Revit rather than simply connected to it, allowing users to be able to use it directly within Revit rather than export the Revit model to an external application. Located within the Revit Add-ins ribbon, opening FenestraPro Premium automatically loads the model that is being developed into the tool and “reads” it, extracting relevant project information such as location and orientation (as was illustrated in Figure 1), information about the building geometry and materials that is contained in the Revit model, and any energy settings that may have been specified in the Revit Energy Settings dialog (Figure 2). All of this information is clearly displayed in the tool where it can be verified to ensure that it is accurate, or it can be edited if required.

Figure 2. FenestraPro Premium can read any energy settings that have been specified in Revit for the project.

Additional non-geometric information that may not be available in the Revit model but which is required by FenestraPro Premium for its analysis include the building type and occupancy patterns during the day and throughout the year, which can be added directly in the tool. Subsequently, the optimal wall to window ratio is established based on the thermal performance of the building as a whole and the facade, which in turn takes into consideration the volume of the building and the area of the envelope. The minimum performance values are calculated and displayed, and the designer can choose to improve the thermal performance of the façade to achieve international standards and best practices. FenestraPro Premium provides access to the most common standards including ASHRAE 90.1, IECC Codes, UK Part L, Title 24, and PH Commercial Standards, and provides guidance on meeting the selected standard by flagging the values that are not in range, as shown in Figure 3.   

Figure 1. The building performance values that do not comply with the selected standard are flagged in red.

For a conceptual massing model, the established wall to window ratio can be applied directly to the building to dynamically see solar and daylighting performances of its different facades and surfaces, as shown in Figure 4.

Figure 4. The established wall to window ratio can be directly to the model at the conceptual design stage.

For a model at the detailed design stage, where the wall to window ratio and location of the glazing has already been established, FenestraPro Premium can be used to drive the solar heat gain and visible light transmittance of the glazing, as well as the required thermal performances of all elements of the façade, including framing, spandrels, etc., of the curtain wall assembly (Figure 5).

Figure 5. The use of FenestraPro Premium for a detailed Revit model allows aspects such as the type of material and the type of glazing for an entire façade, or an individual surface within the façade, to be adjusted to meet the required thermal performance.

The actual changes in element properties can be made within Revit, as shown in Figure 6. It should be emphasized that FenestraPro Premium is not an editing tool, so you cannot use it to change the geometry of the model, unless you are using special FenestraPro Premium libraries for creating doors and windows, which can be resized through the tool, as shown in Figure 7. However, the design can be modified using Revit tools even when FenestraPro Premium is in use—it will just work with the updated information. Also, the link with Revit is two-way, so any non-geometric change that is made in FenestraPro Premium is written back to the Revit model.

Figure 6. Changing the type of glazing for a curtain wall panel family in Revit.

Figure 7. Changing the physical dimensions of a window in FenestroPro Premium, which is only possible for FenestraPro library objects added to the Revit model.

Additional capabilities in FenestroPro Premium include the ability to consider shading from surrounding buildings, understand the effects of different shading devices in reducing solar heat gains and daylighting, and an easy-to-use reporting capability that allows different façade design options to be compared side by side, not just visually, but with detailed data including quantified table of each façade, the area of glazing for each, and the performance requirements of that glazing (Figure 8).

Figure 8. The report generated from FenestroPro Premium in Excel format provide an overview of all the options on the first tab and detailed data for each option in a separate tab.

Generative Design

The current version of FenestraPro Premium, Version 3, has some generative design capabilities, as shown in Figure 9. The top image shows the ability to add windows to multiple facades, based on a target internal heat gain and window size and spacing—the application generates a preview of the number of window openings of this size to achieve the closest result to this target. Actual window objects can then be added to the model in these openings automatically. The lower image shows a similar capability, except that the window openings are automatically generated for a single façade, taking into consideration the target internal heat gain and window size and spacing as before, but with the added criterion of the number of windows, which the user can manipulate to achieve the desired aesthetic result.

Figure 9. The current generative design capability in FenestraPro Premium allows windows to be automatically generated based on target heat gain value and window size, for multiple facades (top image), and for a single façade (lower image), which also allows the number of desired windows to be specified.

While this feature, by itself, does not really qualify FenestraPro Premium as a generative design tool, it does plan to add more generative capabilities in upcoming releases including the generation of glazing according to daylighting performance and generating shading configurations in addition to glazing to satisfy desired heat gains and daylighting, including aspects such as the depth, number, and angle of louvers.

Thus, given its current generative design capabilities which are still very limited, FenestraPro Premium is still primarily an analysis tool, tool, joining the ranks of other energy-related plug-ins or add-ins to BIM applications such as eLum for lighting analysis, Vabi for daylighting and thermal comfort, Sefaira for conceptual stage energy analysis, and so on. And this, despite the competition, is not a bad thing. Performance requirements for buildings are becoming increasingly stringent, and the more tools in our arsenal we have to meet these requirements, the better.


While I was somewhat disappointed to find that FenestraPro Premium does not have that many generative design capabilities yet, I was glad to see that it had made a start and was planning to expand them in future releases. From a technological standpoint, developing a generative design tool is not that difficult, especially for an “algorithmic” (calculation-driven) analysis such as energy. If I was able to develop a prototype tool as an architectural student with a limited knowledge of programming over 20 years ago, I would imagine it to be a lot easier for experienced computer professionals to develop similar tools now, even if they are a lot more sophisticated, handle multiple criteria, and can be used by AEC professionals on real-world projects.

Of course, it’s another question if the industry is ready for such tools yet, if AEC firms want to use them and are willing to pay for them, making them a viable business proposition. Technologists like me have the luxury of reveling in technology for its own sake, but at the end of the day, it is practicality and cold hard cash that will determine when and how we will see generative design become commonplace in the AEC industry.

About the Author

Lachmi Khemlani is founder and editor of AECbytes. She has a Ph.D. in Architecture from UC Berkeley, specializing in intelligent building modeling, and consults and writes on AEC technology. She can be reached at lachmi@aecbytes.com.

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