The NF DTU 39 standard "Glazing and Mirror Work" is the technical reference framework for glazing installation in France. It applies to both new construction and renovation, and directly covers glass facades. For film installers, glaziers, architects and project owners, familiarity with this standard is key to ensuring compliant works and the insurance coverage that comes with it.
Scope and Exclusions to Know
The NF DTU 39 standard is organized into several parts published at different dates: Parts 1-1 and 1-2, covering installation requirements and material selection, were revised in March 2017 and represent the current version for these sections. Parts 4 and 5 — the sizing guide and the safety guide (FD DTU 39 P5) respectively — date from 2012 and complete the normative framework. The standard applies to glazing providing weather protection, installed at a minimum inclination of 5° from the horizontal, as well as interior glazing of any inclination and insulating glazing incorporating glazing bars. It covers all of French territory, including overseas departments, for new construction, renovation, rehabilitation or maintenance work (source: Batirama).
However, certain works are explicitly excluded from DTU 39's scope:
- glazing incorporating an adhesive film on one or more faces
- toughened glass installations
- curved, heated or triple-gas-space insulating glazing units
- suspended glazing
This last point is directly relevant for glazing professionals: as soon as an adhesive film is applied to a face, the installation falls outside DTU 39's scope. However, the calculation methods in Part 3 of the standard remain the essential technical reference for assessing thermal compatibility before any work on an existing facade.
The Five Parts of DTU 39 Used on Site
NF DTU 39 is organized into five complementary documents:
- Part 1-1: technical installation requirements (design, wedging, sealing)
- Part 1-2: general material selection criteria (glass products, sealants, packers, fixings)
- Part 3: thermal stress calculation guide
- Part 4: glazing sizing guide (climate loads, wind, snow)
- Part 5 (FD DTU 39 P5): safety guide for project managers
For glass facades, Parts 3, 4 and 5 are of particular technical relevance.
Installation: Key Points from Part 1-1
Part 1-1 sets out the contractor's obligations before and during installation. Prior to work, the contractor must have information on the required glazing performance, expected climatic and thermal loads, and the nature of the framing. During execution, no direct contact between glass and any metallic or mineral component is permitted: a compatible interposition material is mandatory. Sealant systems must be applied at temperatures above 5 °C. Setting blocks are mandatory to transfer the weight of the glazing to the frame and distribute loads (source: Batirama).
Safety Requirements: Part 5
[Image suggestion: detail of a glazed facade with laminated glass balustrade and DTU 39-compliant fixings]
The safety guide (FD DTU 39 P5) defines requirements for glazed partitions playing a protective role. For balustrades, the standard notably mandates the use of laminated glass, a minimum height of 1 metre, and horizontal impact resistance compliant with the technical clauses. In risk zones — publicly accessible low-level areas, staircases, glazed railings — laminated or toughened glass is systematically recommended.
Thermal Breakage Risk: What Part 3 Calculates
Part 3 of DTU 39 provides a thermal stress calculation method, essential for anticipating the risk of thermal breakage. This phenomenon occurs when a temperature differential develops between two areas of the same glazing unit: typically between the centre, exposed to solar radiation, and the edges held within the frame.
For standard float glass, the critical threshold is around 35 to 40 °C differential between zones, depending on the glazing characteristics (source: DTU 39 P3 and Solar Screen technical documentation). Aggravating factors include partial shading, intense reflections and sudden temperature variations — particularly the combination of interior air conditioning and direct solar exposure. The characteristic crack from thermal breakage starts perpendicular to the glass edge.
Compatibility of Solar Films with Glass Facades
Applying a window film alters the thermal behaviour of the glass. A strongly absorbing film applied to the interior face retains some solar energy after it has passed through the outer layer, raising the temperature of the glazing itself. This additional load must be factored into the thermal stress calculation under Part 3 of DTU 39 methods, before any installation on a facade.
For insulating glazing units, highly reflective, low-absorption metallic films offer broader compatibility with standard facade glazing, subject to systematic compatibility verification. The Solar Screen solar control film range for facades provides, for each reference, the solar absorption and light transmission values needed to assess this compatibility in line with the NF DTU 39 P3 calculation principles.
For a deeper look at verification protocols by glazing type, the article Toughened Glass and Window Film: A Winning Combination? presents the applicable technical criteria based on glass type.