3D-Printed Buildings and Codes

Why approval runs through alternative routes

Most building codes describe materials and methods that existed when they were drafted, so printed walls often have to be approved as an alternative. The International Code Council's Building Safety Journal explained in 2020 that 3D construction technology was not included in the 2018 or earlier editions of the International Building Code or International Residential Code. To fill the gap, ICC Evaluation Service staff developed acceptance criteria AC509 under the alternative materials provisions of IBC Section 104.11, with results published as evaluation reports that code officials can consult. Before committing to a printer, ask the maker whether its wall system already holds such a report and for which building types.

What AC509 and UL 3401 test

Evaluation criteria aim to prove that printed material and walls behave predictably. According to the same ICC article, AC509 calls for material tests including compressive strength, freeze-thaw resistance, shrinkage and the effect of the time interval between printed layers, along with in-plane, out-of-plane and axial compression tests on walls, fire resistance and special inspection. As the ICC article describes it, AC509 applies to interior and exterior 3D concrete walls in one-storey, single-unit homes. UL 3401, Outline of Investigation for 3D Printed Building Construction, looks at a wider set of printed elements, from walls and partitions to floors, roofs, columns and beams, but it does not assess compliance of the structural design.

ISO/ASTM 52939 sets quality on site

Approval comes more easily when the printing process itself is controlled and documented. ISO/ASTM 52939:2023, Additive manufacturing for construction: qualification principles, structural and infrastructure elements, sets quality assurance requirements for building projects that use additive manufacturing, covering activities within the printing site, which the standard calls the additive construction cell, and across the wider project. It applies to load-bearing and non-load-bearing elements in homes and commercial buildings, though not to metals, and it leaves design approval, material testing and health and safety to other rules. Ask whether the maker of the COBOD BOD2, ICON Vulcan II or CyBe RC 3Dp you are considering can show a quality plan built on it.

Bring the building authority in early

Early contact with the building authority saves more time than any printer speed. Share the wall system's evaluation report or test data, the structural engineer's design basis, the quality plan and how inspection will happen during printing, since an inspector cannot see inside a finished wall. Agree hold points, such as checking reinforcement placement or sampling material from each batch, and who will record them. Ask how openings, fixings, services and insulation will be approved, because these often follow conventional details. Expect the first printed project in a district to take longer to approve, and keep the full record afterwards so later applications can point to an accepted precedent.

Sources and further reading

• ICC Evaluation Service is primed for 3D printing — International Code Council (Building Safety Journal).
  How ICC-ES acceptance criteria AC509 tests 3D-printed concrete walls that the IBC and IRC did not yet cover.
• UL 3401 Outline of Investigation for 3D Printed Building Construction — UL (listed on the ANSI Webstore).
  Scope of UL's investigation outline for evaluating 3D-printed walls, floors, roofs, columns and beams against building codes.
• ISO/ASTM 52939:2023 Additive manufacturing for construction: qualification principles, structural and infrastructure elements — International Organization for Standardization.
  Quality assurance requirements for building projects that use additive manufacturing, on the print site and across the project.

Common questions

Are 3D-printed houses legal?

Yes, where the building authority accepts that the design meets the applicable code, often through an alternative-method route backed by test evidence or an evaluation report. Rules vary between countries and districts, so confirm the approval path locally before buying land or a printer.

Do 3D-printed walls need steel reinforcement?

It depends on the design, the loads and local seismic and wind requirements. Some printed walls carry reinforcement placed during or after printing, while others rely on a separate structural frame. Your structural engineer and the evaluation evidence for the wall system should settle the question.