Curtain wall systems are the signature feature of contemporary architecture. From stunning glass towers that make up the skyline of our cities to the sophisticated facades of institutional buildings, these non-load-bearing exterior surfaces are the perfect combination of performance, sustainability, and aesthetics. However, getting from an architectural concept to a finished curtain wall system that performs well is a process full of many nuances. It requires precise and comprehensive documentation that goes far beyond 2D drawings and encompasses the whole spectrum of a project's lifecycle.
Accurate documentation is the basis of the success of the project. It is a tool of coordination between the facade system, the structure of the building, its mechanical, electrical, and plumbing systems, and other trades. It defines the critical points of the facade's waterproofing, thermal performance, and its capability of compensating for the building movements. It gives the exact information required for fabrication and installation of the curtain wall system.
Modern Building Information Modeling technology has radically changed the documentation process. Thanks to it, the industry has moved from traditional 2D drawings to intelligent 3D models that drive fabrication and construction.
Understanding Curtain Wall Systems and Their Design
So, let's start with the definition and key features of curtain wall systems.
A curtain wall system is a lightweight non-load-bearing external cladding of a building. It protects the interior of the building from the external environment and acts as a shield against wind, rain, and seismic forces. Also, it provides thermal insulation and maximizes daylighting. One of the most important features of the curtain wall system is the fact that it is non-load-bearing. It hangs from the structural frame of the building and carries none of the gravity loads of the building (floor and roof).
It means that it must be flexible enough to compensate for the building movements caused by wind and seismic forces, as well as the differential vertical movements of the facade and the building structure.
Modern curtain wall systems consist of multiple materials that provide specific performance qualities. The framing of the curtain wall system consists mostly of aluminum – a lightweight and durable material that is easy to extrude into different shapes. Infinite recyclability is another important advantage of aluminum. As for the infill material, it is usually made of glass, which comes in many types, including tempered, laminated, and insulated glass units with low emissivity coating to control heat and solar radiation. Also, spandrel panels of aluminum or other materials are used to hide structural elements and floor slabs. All elements of the system are fastened with gaskets, sealants, and thermal breaks for air and moisture tightness and energy efficiency. The key components of the curtain wall are mullions, transoms, and anchors that fasten it to the building structure.
Types of Curtain Wall Systems and Documentation
There are several types of curtain wall systems and each one has specific documentation needs.
There are two main types of curtain wall systems – stick-built and unitized systems.
Stick-built systems consist of individual components – framing members, glass panels, and other accessories that are shipped to the site and assembled there. While this approach is more flexible and allows for on-site adjustments, it requires a lot of on-site labor. The documentation of the stick-built system should include a lot of site assembly drawings. They should have clear mullion and transom layouts, installation sequence, connection details, and provisions for field tolerances. Every single component should be properly identified and located in order for it to be assembled properly by the installation crew.
Unitized systems are a more modern approach to facade construction. In this case, large preassembled units consisting of frames, glass panels, and accessories are manufactured in a factory-controlled environment and then shipped to the site to be installed. Such units provide a faster building enclosure and more control over quality. Documentation of such curtain wall systems is quite extensive and should be very detailed. It should include shop drawings, panelization map showing the location of every unique unit, unique ID of units, details for lifting points, interfaces with the building structure, and connections between panels. Since units are preassembled in the factory, the fabrication models should be very precise.
However, there are also other curtain wall systems, which have specific documentation needs. Point-fixed glass systems, often known as spider glazing, consist of glass panels supported by metal fittings at their points and not along the perimeter, providing maximum transparency. Structural glazing systems are similar and consist of glass panels bonded to the frame with silicone. Their documentation should contain detailed information about the point connections, load transfer, and, in some cases, glass drillings patterns. Semi-unitized systems that combine stick-built and unitized systems also have specific documentation needs.
Curtain Wall Documentation Workflow
The process of curtain wall documentation is quite phased.
At the earliest stages, the design intent should be established. The architect and facade engineer collaborate to prepare massing models, typical wall sections, performance requirements that are often incorporated into BIM model. It is a time to research materials, analyze the performance and design solutions and to coordinate the facade's shape and performance with the architectural and structural aspects of the project. It is the best time to solve all large scale coordination issues and make sure that the facade design works together with the building's massing and meets the requirements of the client.
As the design is developing, the BIM model becomes more detailed and coordinated. At this stage, the curtain wall BIM model is coordinated with structural models, MEP models, and other trades to resolve conflicts and make sure that the facade is constructable. At this stage, several deliverables should be prepared, such as floor by floor elevations, detailed sections through special conditions (corners, parapet, etc.) and loading schedules. Very important aspect of this stage is clash detection, during which all conflicts between building systems are resolved in a BIM model and the risks of conflicts during the construction are eliminated.
At this stage, detailed drawings, which are going to be used for fabrication and assembly of the curtain wall system, are produced. It includes panelization, mullion and transom cutting list, exact size and type of the glass, hardware schedule and many other details. BIM model is developed to LOD 300 or 400, containing exact profiles, joint details, connection details. Such a detailed BIM model allows for fabrication services to generate fabrication data for CNC machines and assembly instruction for installation.
And finally, at the last stage, the documentation that is needed for on-site installation of the system and the documentation of the final state of the building is prepared. It includes set out drawings, anchor locations, erection sequences and quality control checklist. As the changes are inevitable in the field, BIM model is updated during the construction to reflect the changes that occurred. The as-built BIM model becomes a great asset for the building owner for future facility management, maintenance, and renovation projects.
How Building Information Modeling Changes Curtain Wall Documentation
BIM is a technology, which drives the modern process of curtain wall documentation providing a huge leap ahead from the traditional methods.
Unlike traditional documentation, which is represented by 2D drawings that can be difficult to coordinate, BIM services provide the single and shared 3D model, which provides the possibility to visualize the entire facade system. Data-rich model gives an opportunity to analyze, visualize, and communicate the information about the building much more effectively. BIM services for curtain walls are the key to realization of complex curtain wall designs.
Using BIM services for curtain wall systems, it is possible to get a lot of deliverables such as coordinated 3D models, detailed sections, panelization diagram, quantity take-off, schedule for glass, aluminum, and hardware. BIM model can also be used for performance analysis such as thermal, solar, and wind load analysis and code compliance check.
There are definite advantages of using BIM services for every project stakeholder. Architects get an instrument of preserving the design intent and rapid iterations. Contractors get clear installation sequences, reduced clashes, and rework, providing a predictable delivery of the project. And for fabricators BIM services provide a precise cutting list and detailed curtain wall models, making fabrication process easier.
Bridging Gaps in Facade Documentation with BIM
Curved, faceted, or any other complex shapes for facade surfaces are challenging to document using conventional methods. BIM tools allow working with highly detailed models and generating necessary fabrication information for the unusual geometry of panels and their connections.
One of the most common causes of construction errors is a lack of coordination between the building facade and the building's primary structure and mechanical, electrical, plumbing systems. In particular, there are many conflicts between anchors, slab edges, and MEP penetrations. Coordination with BIM allows working in the same environment for all the disciplines involved. Clash detection finds the potential conflicts beforehand, preventing the need for change orders and costly on-site rework.
The proper design of the facade involves satisfying various requirements for wind load resistance, water and air infiltration, fire ratings, and thermal performance of the curtain wall. Rich data contained in the BIM model allows associating this data with the geometry, streamlining calculations, developing testing plans, and creating required documentation.
Best Practices for Curtain Wall Documentation
Work with the consultants for the curtain wall and BIM services providers in the earliest stages of the design development. Their experience is extremely helpful to ensure that the design is both performative and constructible. It is much easier to avoid mistakes before embedding them into the design and then wasting additional time and money fixing them.
Make sure that the panels have consistent IDs, all drawings and models use the same grids and views. This eliminates confusion and helps to streamline the process of communication between team members. Having the consistent names and references allows finding required components and understanding connections within the documentation easily.
Clearly define who is responsible for modeling what and at what LOD to prevent gaps and duplication of the effort between the architect, the facade contractor, and other trades. It is very important not to overlook any information but also not to waste any efforts on the unnecessary work.
Perform regular model checks and audits to validate tolerances, clearances, and data completeness before issuing the documentation for fabrication. This way, it will be possible to achieve high quality of final deliverables.
Professional Documentation Services can Make the Difference in Your Project
The process of curtain wall documentation is a challenging but crucial step that defines the success of the most visible and performative part of the building. From the first sketch up to the final as-built documentation, all the details matter to ensure the high performance, easy construction, and long life of the facade. Transition from conventional 2D drawings to the intelligent 3D BIM models made this process more efficient.
Leveraging the professional services for the curtain wall modeling and facade BIM will allow mitigating the risks, saving costs, and achieving the best results in architecture. High level of expertise offered by such services allows achieving not only the accuracy of the documentation but also its optimization for fabrication and installation. Investment in the high-quality documentation will pay off in reduced construction time, minimized change orders, and the highest quality of the final result.
Frequently Asked Questions
1. What is the difference between stick and unitized curtain wall documentation?
The main difference is related to the place of the assembly. The documentation of the stick-built system requires more detailed drawings of the site assembly, mullion and transom layout, and field tolerances. The documentation of the unitized system should include more shop drawings and panelization map with unique IDs of each unit.
2. What LOD is used for curtain wall BIM models?
The LOD depends on the project phase. Typically, LOD 300 is used for the coordinated design and permitting while the LOD 350 or 400 is used for detailed fabrication and installation of the curtain walls since it contains all the information about the exact geometry, materials, and connections.
3. How do facade BIM services help with coordination with structure and MEP?
Using facade BIM services, you receive the coordinated 3D models containing the facade integrated with the structure and MEP systems of the building. Using such models allows performing clash detection and resolving the potential conflicts in the digital model preventing imprecise anchor locations and unclear interfaces with slabs, beams, and services.
4. What documents are included in a complete shop drawing set?
The complete shop drawing set typically includes panel layouts, detailed mullions and transoms, glass schedule listing sizes and types of glasses, connection details of anchors and interfaces, hardware list, and performance requirements for the weather-tightness and thermal performance.
5. Can BIM be used for the complex curtain walls with curved geometry?
Yes, using the parametric BIM tools, it is possible to create highly detailed models of the complex shapes like curved or faceted facade surfaces. Such tools allow representing the geometry and generating fabrication information for non-standard panels and connections.
6. How does curtain wall documentation help with facility management after the construction?
Using the accurate as-built BIM models and drawings with rich data serves as an important asset for building owners and facility managers. It is a detailed record of the installed system with information about materials and components, which is very helpful for maintenance, replacement, or upgrade of the system in the future.
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