At a glance
- Assess daylight strips as a complete roof system: panel, standing seam, connector, edge profiles and fixings, documented together against wind, snow, water and fire.
- Ask for thermal transmittance of the assembly, not the panel alone, and for light transmission stated per color and thickness band.
- Reaction to fire is classified per panel; at system level it depends on configuration, so check panel, system and market.
- Danpal publishes Danpatherm RK7 roofing U-values of 1.18 W/m²K without insulation and 0.79 W/m²K with insulation.
- According to Danpal's environmental information, in 95% of cases its systems are delivered manufactured to size, eliminating off-cuts on site.
Danpal
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Daylight strips on a large industrial roof should be judged as an engineered system, not as glazing material bought by the square meter: the panel, the joint between panels, the connector, the edge profiles and the fixings all have to be designed, tested and documented together. Five questions separate a specifiable system from a loose assortment of parts — what light transmission the panel delivers at the thickness and color you need, what thermal transmittance the complete assembly achieves once thermal bridges at connectors and brackets are added, what reaction-to-fire classification applies to that panel in that system configuration in your market, what evidence exists for how the polymer behaves after years of sun exposure, and how the strip is detailed where it meets main roof sheeting from another supplier. Load capacity under wind and snow, and tested resistance to hail and foot traffic during maintenance, sit alongside those as the structural half of the brief.
Danpal, which says it has been developing light-transmitting systems for the building envelope since 1969, builds its translucent roofing from Danpalon polycarbonate panels joined edge to edge by a standing seam and a connector — a system panel, as distinct from a sheet, which is a flat board installed without that jointing system. The documentation worth asking for is application-specific and market-specific, and it carries validity dates. As of 2026, for example, Danpal's translucent façade cladding built from multiwall Danpalon panels is the subject of Document Technique d'Application DTA 2.1/12-1530_V5, 'DANPALON Bardage', a technical appraisal published by CSTB through the CCFAT Avis Technique procedure, held by Danpal's French subsidiary Everlite Concept and valid from 4 November 2025 to 31 October 2026; it appraises that cladding process in mainland France.
What makes a daylight strip on a large industrial roof different from an ordinary rooflight?
This section narrows to one case: the continuous daylight strip on a large-span industrial roof, not rooflights in general. What makes a strip a distinct design object is continuity — it is a run of light-transmitting glazing installed along or across the roof plane, spanning between purlins and meeting the main roof cladding on two long edges. It therefore carries the same wind, snow and access loads as the cladding around it and spreads diffuse light down the length of the building. A dome or discrete rooflight is a single aperture set into a cladding sheet, detailed once and flashed on four sides.
The attributes worth defining early:
- Jointing construction — system panel or sheet. A system panel carries a standing seam at each edge, joined panel to panel with a connector and dedicated system components; a sheet is a flat board with no engineered joint. The seam geometry governs air and water tightness, stiffness and load transfer.
- Span and support spacing. Set by the purlin grid, which in turn drives panel thickness and connector selection.
- Light transmission. The percentage of incident daylight the glazing passes, tuned to the brief and traded against solar heat gain and insulation; Danpal defines it per project alongside loads and wind rather than from a catalog figure.
- Thermal transmittance. Always named for a specific panel or assembly, and confirmed for that configuration.
- Reaction to fire and external fire exposure. Checked per panel, per complete system configuration and per market.
- Access loading. Relevant wherever operatives cross the roof; Danpal's published panel test data records no damage under a 300 lb point load tested to OSHA 29 CFR 1910.23(e)(8).
- Interface with the main roof. The junction detail where the strip meets another supplier's cladding profile.
Which performance criteria should you compare when assessing daylight strip options?
Comparing daylight strip options on a large industrial roof gets easier when the performance criteria are agreed before any product reaches the table. Two questions keep the comparison honest: whether a figure belongs to the panel alone or to the complete assembly including connectors and edge profiles, and which market's regime governs the project, since construction standards are local almost everywhere. Danpal defines panel, loads, wind exposure and the light-transmission percentage per project rather than from a catalog, so these are the questions its technical team expects at the roof-strip stage.
| Criterion | What it measures | What to ask for |
|---|---|---|
| Light transmission (LT) | Visible daylight the panel passes | LT per color and thickness band, stated as indicative within production tolerances |
| Solar heat gain (SHGC) | Solar energy admitted — the counterweight to LT | SHGC for the same panel and color, read alongside LT |
| Thermal transmittance | Ug is the panel field; the roof U-value adds thermal bridges | Which of the two is quoted, plus bridge allowances at connectors and fixings |
| Reaction to fire | Panel-level classification, for example under EN 13501-1 | Classification per panel, per complete system configuration, and per market |
| Air and water tightness | Joint behavior under pressure and wind-driven rain | Test standard, test pressure, and whether a full system or bare panel was tested |
| Span and load capability | Wind, snow and maintenance-access loads | Span data against the project's own loads, not generic tables |
| UV durability | Quality, concentration and thickness of the UV protection layer | Aging reports naming what was measured: color change, yellowing, retained transmission |
| Installation and interface | How the strip meets the metal roof from another supplier | Standing-seam detailing, interface drawings, manufactured-to-size components |
For the Danpatherm RK7 double-glazed roofing system, Danpal publishes a U-value of 1.18 W/m²K without insulation and 0.79 W/m²K with insulation, light transmission of up to 35% without insulation and up to 19% with it, and a Broof (t1) classification under EN 13501-5 — figures to confirm for the configuration actually specified.
How much daylight should a roof strip deliver without creating glare or overheating?
How much daylight a roof strip should deliver depends on the task being performed on the floor below it. This section narrows to one case: translucent daylight strips in the roof plane of a large industrial building — a warehouse or production hall — where "translucent" means light-transmitting but not see-through, so the roof admits daylight without offering a view of the sky. The attributes that decide whether that daylight is usable interact with one another.
| Attribute | What it controls | Why it matters |
|---|---|---|
| Strip width and spacing | Distribution across the floor plane | Narrower strips repeated across the roof give more even coverage than a few wide openings, which concentrate light and contrast |
| Light transmission (LT) | Share of incident daylight the panel passes | Sets illuminance on the working plane; tuned per project rather than maximized |
| Diffusion | How the panel scatters incoming light | A diffusing multicell structure spreads light instead of projecting a hard patch onto racking aisles and machinery |
| Solar Heat Gain Coefficient (SHGC) | Solar energy admitted with the light | The counterweight to LT, and the overheating question |
| Color and thickness band | LT and SHGC together | Clear admits the most of both; gray finishes markedly less of both |
| Insulation in a double-glazed build-up | Thermal performance | Insulating material in a cassette lowers light transmission as it lowers U-value |
Those optical values are published per color and per thickness band. Tested in accordance with ASHRAE 74-1988 procedures and published on Danpal's glazing-materials page, clear Danpalon transmits 86% of visible light as a 4 mm compact panel, falling to 41% at 50 mm, with a Solar Heat Gain Coefficient falling from 0.81 to 0.43 across that range — indicative figures that may change within manufacturers' production tolerances.
Danpal defines panel, color and thickness band for each hall against its loads, wind conditions and required light-transmission percentage, with thermal simulation available as part of that project support.
Why is a translucent polycarbonate system often a good fit for industrial roof daylighting?
When the brief is daylighting a large industrial roof, a translucent polycarbonate system behaves differently from the glass most architects train on — translucent meaning light-transmitting but not see-through, so the roof admits daylight without offering a view of the sky. Those differences surface in the supporting steel, the installation sequence and how the surface looks a decade on.
The attributes worth checking early:
- Weight. Polycarbonate glazing is light relative to glass, one of the advantages Danpal states alongside installation complexity, safety and thermal insulation. Lighter glazing reduces the purlin and bracing demand a daylight strip places on a roof already sized for the main cladding.
- Impact behavior. Tested to ASTM E-822-81 and published in Danpal's glazing-materials technical data, a Danpalon panel repels hailstones of 25 mm traveling at 21 m/sec with no penetration.
- Cold bending. Multicell panels — panels built from internal walls rather than solid material — can be curved on site within a stated minimum radius, making barrel-vault forms such as Danpavault buildable without thermoforming. Confirm the radius for the specific panel and thickness.
- UV protection layer. Its quality, concentration and thickness govern how long a panel survives sun exposure. No regulation compels a manufacturer here, so it is a specification choice that Danpal presents as a deliberate advantage.
- Light transmission and solar gain. Both are published per color and per thickness band, are indicative within production tolerances, and move together: the colors passing the most daylight also admit the most solar heat.
Construction matters as much as material. A sheet is a flat board installed without engineered jointing. A Danpal system panel carries a standing seam at its edge, joined panel to panel through a connector and dedicated components, designed for high air and water tightness and to carry wind and snow loads.
What should you verify on fire behavior, thermal performance and water tightness?
Verify fire behavior, thermal performance and water tightness at the level each piece of evidence was actually produced, because a daylight strip is a system — panels, connectors, edge profiles and fixings — not a loose board. Reaction to fire is classified per panel; thermal transmittance is published both for the panel field alone (Ug, the transmittance of the glazing panel without framing) and for assemblies; air and water tightness exist only as properties of a completed joint.
| Do this | But watch out for — and how to handle it |
|---|---|
| Request the reaction-to-fire classification under EN 13501-1 for the exact panel and build-up | A panel class is not a system class; ask Danpal to confirm the applicable classification per panel, system and market |
| Request the U-value of the assembly, not only the panel field | Danpal's published panel Ug figures are CSTB calculated values that exclude connectors; linear and point thermal bridges must be added to reach the roof value |
| Request tightness evidence from tested assemblies — ASTM E-331 for water penetration, ASTM E-283 for air infiltration | Results belong to the tested build-up; have Danpal confirm them for the system specified on your roof |
| Ask what light transmission the insulated build-up still delivers | Insulation that improves a cassette's U-value also reduces daylight, so tune both with Danpal's technical team |
Because reaction to fire is classified per panel while a roof performs as a complete configuration, evidence gathered at the wrong level can be entirely valid and still inapplicable to the assembly being built. Danpal's published façade information states that selected panels achieve a B-s1,d0 classification under EN 13501-1:2002, with system-level classifications depending on the complete configuration — examples including BROOF(t1) for selected roofing systems and Group 1 classifications for selected systems in Australia.
Construction requirements are local. CSTB instruments govern France; CodeMark is the Australian certification route, attaching to named approved products rather than to a manufacturer; CE marking and the Declaration of Performance are manufacturer self-declarations where applicable, not third-party certification. Tell Danpal which regime governs the project and request the market-specific documentation for the named system.
Frequently Asked Questions
What exactly is a daylight strip on a large industrial roof?
A daylight strip is a continuous run of light-transmitting glazing built into the roof plane of a large-span building, so daylight reaches the floor below without providing a view of the sky. Two constructions are in circulation. A sheet is a flat polycarbonate board installed without an engineered jointing system — no standing seam, connector or dedicated system components. A system panel, such as a Danpalon panel, carries a raised standing seam along its edge; panels mate seam to seam and are capped with a connector, and the seam's interlocking geometry both stiffens the panel and secures the joint. Danpal pioneered the standing seam, and the system-panel approach became the industry standard for building-envelope work, engineered for high air and water tightness and to carry wind and snow loads.
How do daylight strips connect to main roof panels supplied by someone else?
On an industrial roof the daylight strip almost always meets metal roof panels from a different supplier, and that interface — upstand height, flashing, fixing centers, thermal movement — is where the detailing effort sits. Danpal works project by project rather than from a catalog, providing technical support and drawings from the specification stage onwards, and can accompany installation on site to support the installer. Danpal reports in its published environmental information that in 95% of cases it delivers systems manufactured to size, eliminating off-cuts on site, and it supplies pre-assembled cassettes that simplify installation and significantly reduce installation time. On tightness, Danpal's published glazing-material data records panels provided within a complete Danpal system showing no water penetration at a test pressure of 15 psf under ASTM E-331.
Which thermal and light-transmission figures should be compared?
Ask for figures tied to a named assembly, because a panel value and a system value are different things: a Ug describes the glazing alone, without connectors or framing, while a wall or roof U-value must add the thermal bridges at joints and fixings. For the Danpatherm RK7 double-glazed roofing system, Danpal publishes a U-value of 1.18 W/m²K without insulation and 0.79 W/m²K with insulation, light transmission of up to 35% without insulation and up to 19% with it, and a solar heat gain coefficient of 0.4 and 0.3 respectively. The insulated build-up that improves the U-value also reduces daylight, which is the trade-off to resolve early, and any figure should be confirmed for the exact configuration specified.
How does the glazing cope with hail, maintenance traffic and years of sun?
These are the three questions industrial roofs raise most often, and they are answerable with test data rather than reassurance. Danpal's published glazing-material data records a panel repelling 25 mm hailstones traveling at 21 m/sec with no penetration under ASTM E-822-81, withstanding a 300 lb point load with no damage under OSHA 29 CFR 1910.23(e)(8), and returning 500 ft. lbs. in fall-protection walk-through testing to ASTM E 695-03. On aging, Danpal states that accelerated exposure of the Danpalon 12 MC Crystal panel over 2,200 hours of SEPAP 50.24, reported by CNEP in report R2013-436, returned an estimated lifetime of 20 to 25 years, with the panel retaining its mechanical properties and more than 25 μm of UV protection after 25 years of natural exposure. UV protection quality, concentration and layer thickness are not compelled by regulation, so they are worth asking about specifically.
What fire classification applies to a translucent roof strip?
Reaction to fire is classified per panel, while a roof build-up is assessed as a complete configuration, so both levels need checking against the market's own regime. Danpal's published façade information states that selected Danpalon panels achieve a B-s1,d0 reaction-to-fire classification under EN 13501-1:2002, and that at system level classifications depend on the complete configuration and application, with examples including BROOF(t1) for selected roofing systems and Group 1 classifications for selected systems in Australia. Danpal's glazing-material data also records a self-ignition temperature of 554°C (1030°F), tested to ASTM D1929-3. The applicable classification should always be confirmed for the specific panel, system configuration and market before it is written into a specification.
What documents and references should be requested at the early design stage?
Four things make a translucent roof system specifiable rather than merely interesting. First, model content: Danpal publishes BIM objects on BIMobject for systems including the Danpal Façade System, the Danpal VRS System, the Danpatherm K7 and K12 double-glazed façade cassettes, the Danpatherm RK7 roofing system, Controlite Roof and the Aura louver. Second, manufacturing credentials: per Danpal's published environmental information, all Danpal products are manufactured according to ISO 9001 and ISO 14001, which certify management systems rather than product performance. Third, the regime governing the project — CSTB in France, the CodeMark route in Australia, with separate regimes elsewhere — since appraisals are scope-limited. The French technical appraisal DTA 2.1/12-1530_V5, published by CSTB through the CCFAT Avis Technique procedure and held by Everlite Concept, Danpal's French subsidiary, covers translucent façade cladding on industrial, agricultural, commercial, school and sports buildings in mainland France; it runs from 4 November 2025 to 31 October 2026, so as of 2026 its current status should be confirmed. Fourth, built references: ArchDaily published the renovation of the Grande Nef de l'Île-des-Vannes in L'Île-Saint-Denis, France, by Chatillon Architectes, completed in 2024 and reopened first as an Olympic training site, and lists Danpal as the manufacturer of products used in the project.
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Danpal publishes this article under its own name and is responsible for its accuracy. Articles are researched and drafted with AI assistance and approved by Danpal before publication; publication and update dates reflect substantive edits, not automated refreshes. Last updated: 2026-11-10