April 25, 2019
For many, the concept of 3D printing of physical objects – also referred to as additive manufacturing – may seem like something years into the future. Guess what? It’s here now and small desktop 3D printers are available from online retailers for less than USD $200. Many of you may have seen online videos of 3D printed buildings and thought this is a construction technique of the distant future. Guess again, 3D building construction is already making its way into the market.
If you have not seen how buildings can be constructed using 3D printing, search the internet for “3D Printed Building Videos.” The results may be eye-opening for many of you. This innovative construction technique is rapidly moving from a conceptual and experimental stage to a viable building construction method.
Before stakeholders, including code authorities, can fully embrace this new technology, there needs to be reliable assurance that this new construction technique complies with all applicable building construction code requirements, many of which are prescriptive in nature. Determining that 3D printed building construction is equivalent to the code requirements for traditional construction can be done using the alternate materials and methods provisions in model codes, but there is currently little guidance on how to confidently approach this determination.
UL takes the lead in developing requirements
Fortunately, UL has been examining this issue since 2017 and is developing a methodology for evaluating 3D printed building construction. These requirements are included in the draft UL 3401, Outline of Investigation for 3D Printed Building Construction, expected to be released later this year. The goal is to eventually publish UL 3401 as a bi-national consensus Standard.
UL 3401 covers the evaluation of building structures and building assemblies such as panels, walls, partitions, floor-ceilings, roofs, columns and beams that are fabricated using an additive manufacturing or 3D printing process. UL 3401 is intended to provide the information needed to determine that a 3D printed construction complies with one or more specific model building or residential codes, or government regulations covering the building construction. This includes documenting compliance with performance standards referenced in these codes.
The intent of the evaluation
The UL evaluation of the additive manufacturing or 3D printing process determines that the 3D printing equipment, additive manufacturing materials, fabrication processes, tolerances and production controls will adequately and consistently produce building structures with properties equivalent to the samples initially tested or evaluated and documented in the report of findings. The properties evaluated include mechanical (structural) strength, fire performance, air and water barrier compliance, thermal insulation, indoor air quality, durability and integrity. Among other things, the UL 3401 evaluation addresses the following:
The 3D printing process relies on software, firmware and controls to design and construct the 3D printed structures. These include:
- Modeling software used to design the building and its structural elements
- Slicing software used to identify the layers and areas to be 3D printed
- Software, firmware and controllers used to provide printing instructions to the 3D printers and production equipment
UL 3401 includes requirements to monitor, display, and provide reports on key production parameters that are critical to ensure that the building assemblies are consistently produced within the design specifications and tolerances. It also requires documentation to be available to confirm the production parameters used during the build.
3D printing equipment
The 2021 International Fire Code requires industrial 3D printers to be Listed (Certified) and Labeled in accordance with the UL 2011, Outline of Investigation for Factory Automation Equipment. Accordingly, UL 3401 requires 3D printer to comply with UL 2011; production equipment to be used in accordance with a manufacturer’s instructions; and nozzles, hoses, fittings, curing equipment and other components to be compatible with the 3D printer.
The UL 3401 evaluation closely examines the fabrication process and establishes production controls to determine that 3D printed structures consistently meet criteria for mechanical strength, fire performance, air and water barrier, thermal insulation, indoor air quality and durability.
Additive manufacturing materials
Additive manufacturing materials (AMM) are evaluated to determine consistency and reproducibility of construction. These materials may include a mixture of common construction materials and proprietary formulations. The UL 3401 evaluation determines that the formulation used at a job site is unchanged from that used during the preparation of test samples. Proprietary AMM is required to be covered by a third-party certification program to confirm that the formulation does not change from that used to produce all test samples.
Testing of 3D printed construction is required to determine compliance with building code requirements covering fire performance, building envelope performance (such as air, water, and thermal), indoor air quality and others mandated by the applicable codes adopted by the jurisdiction. For example, UL 723 (ASTM E84) and UL 263 (ASTM E119) testing or certification may be required to establish interior finish performance and fire-resistance ratings respectively.
Because test performance can vary depending on several production factors, UL 3401 requires test samples to be prepared using the production controls, fabrication process and AMM being evaluated. To determine compliance, test sample preparation should be witnessed by the certification organization conducting the UL 3401 evaluation to confirm that the samples are manufactured within documented construction specifications and using the fabrication process and additive manufacturing materials being evaluated.
A 3D printed building construction process that successfully complies with UL 3401 can also be covered by a UL Evaluation Report, providing designers, builders and code authorities with the technical data to competently review and approve 3D printed building construction projects .
For more information on the evaluation of 3D printed building construction, please contact Howard Hopper at [email protected].
Author: Howard Hopper, FPE, UL Regulatory Services Manager