Guide
The one month rule for hard-coated glass
ARG's hard-coated glasses, the SKN and PlanitHerm series from Saint-Gobain, can only be used in an insulated unit (DGU) and must be converted into one within one month of purchase, or the glass is damaged.
What is the one month rule?
The coated Saint-Gobain glasses ARG builds into insulated units, the SKN series and the PlanitHerm series, are what ARG calls hard-coated glass. ARG’s operating rule for them is short and absolute: a hard-coated pane can only be used inside a DGU, and it must be converted into one within one month of purchase. A pane that misses that window is not delayed. It is damaged.
A coated pane that is not converted into a DGU within a month does not get a second chance. The glass is damaged, not just delayed.
Nothing else published on the open web states this rule, which is exactly why this page does. It is an operating fact from the factory floor, not a line from a brochure.
Can I stockpile hard-coated glass?
No, and this is the practical point of the rule. Ordering coated glass ahead of a site date to lock in a price, or holding a few panes “just in case” a design changes, runs the same risk either way: the clock starts when the coated pane arrives, not when it goes into a unit. The working answer is to treat coated-glass ordering and DGU fabrication as one job rather than two purchases separated by a wait. Order once the build-up and the site date are both fixed.
What Saint-Gobain’s own sheets require before a DGU is built
The one month rule is ARG’s own. The maker’s literature for the same coating family adds its own handling requirements, and they point the same way: this is glass that is meant to be processed, not stored.
Saint-Gobain’s sheet for Cool-Lite SKN 154 states that SKN 154 II “must always be toughened or heat-strengthened before assembly into a double-glazed unit”, with the coating on face 2, the surface facing into the cavity.
The SKN 176 II sheet repeats the requirement and goes further: the pane “must always be toughened or heat-strengthened before assembly into a double-glazed unit”, must also be edge-deleted and should always be positioned on face 2 of the unit.
Toughening is a heat process and edge deletion strips the coating from the border so the unit’s seal bonds to bare glass; both happen at the fabricator. In other words: a coated pane is a component of an insulated unit, and the maker specifies it as one.
Does uncut stock have the same clock?
No. Saint-Gobain’s processing guidelines for its Cool-Lite ST coated range give correctly stored, unprocessed stock a much longer shelf life: kept in the stated storage conditions, the glass “is guaranteed for 2 years from the date of reception”. The same document warns that glass stored in humid conditions can degrade, staining or corroding, with pitting on the coated side. And once cutting starts the clock changes completely: cut glass “must be edge worked within 5 days”.
Read together, the figures describe stages rather than a contradiction. Sealed, correctly stored coated stock keeps for years at the maker’s warehouse standard. A pane that has been bought for a unit is on ARG’s one month clock. A pane that has been cut is on a five day clock to the edge works. Each step forward shortens the time the coating can safely wait.
Why use a coated pane at all?
Because the coating is what the unit is for. Saint-Gobain describes its solar control range as “designed to reduce solar heat gain, thereby reducing reliance on ventilation and air conditioning systems”. The coated pane is the layer that keeps a glazed room usable in the afternoon, and the DGU is the assembly that protects that layer for the life of the window.
What ARG builds with these panes, and the configurations they go into, is on the insulated glass (DGU) page. To work out a build-up for a real elevation, start at the glass configurator or send your drawing on WhatsApp.