Privacy window film, without closing the blinds

Every quote starts with what is already in the opening. Single pane, double glazed, tempered, laminated, and low-E coated glass all accept film differently, and a product that performs correctly on one assembly can be the wrong call on another.

The concern on sealed double glazed units is thermal stress. A dark, highly absorbing film raises the temperature of the pane it is bonded to, and on an assembly that is already absorbing heat, that added load is what cracks glass or stresses the perimeter seal. Manufacturers publish which films are cleared for which assemblies, and that is the constraint we work inside rather than around.

Whether the glazing is still under warranty from the window supplier matters too. Some sealed unit warranties are affected by applied film. We raise that before anything is ordered, not after it is on the glass.

Running one film across every window in a building is the most common specification error we are asked to correct. The problem is not the same on each face, so the answer should not be either.

West facing glass takes the hardest hit. Late afternoon sun sits low and enters almost horizontally, which is the worst angle for both glare and heat, and it arrives at the end of the day when the space has already been warming for hours. This is the elevation where the strongest privacy and solar specification is justified.

South facing glass carries the highest total annual solar load in Montreal, but the summer sun angle is high, so less of it comes straight through the opening. In winter that same exposure is doing useful work warming the space, which is a real argument against over darkening it.

East facing glass gets sharp morning glare with much less accumulated heat. North facing glass gets almost no direct solar gain, so film on a north elevation is specified for privacy, UV, or security, and not for heat at all.

Street level and courtyard glass are specified by sightline rather than by compass direction. What decides it there is who can see in, from what distance, and at what height. A ground floor unit facing a sidewalk two metres away is a different problem from a third floor unit facing a parking lot.

Film is applied to the interior face of the glass. The glass is scraped and cleaned first, because anything left on the surface, mineral deposits, paint flecks, adhesive from an older film, will read as a defect once there is film over it. Preparation is most of the labour on most jobs.

Application is wet. A slip solution lets the film be positioned before it is squeegeed down, so expect water on the glass, the sill, and the protective sheeting below. Furniture within about a metre of the glass needs to be moved clear and window coverings taken down or lifted out of the way.

Film is trimmed to a small deliberate gap at the edge of the glass rather than butted hard to the frame. That gap is correct and not a defect. It lets residual moisture leave and keeps the edge from lifting a year later.

The film is not at its final appearance the day it goes on. For the first few weeks it can look slightly hazy, or show small water pockets or a faint texture. That is residual moisture behind the film leaving through the film as it cures, and in Montreal it takes noticeably longer in the cold months than in July.

Do not clean the film during that period and do not try to press the pockets out. Once cured, clean with a soft cloth and a mild soap solution or a non ammonia glass cleaner. Ammonia based products and abrasive pads will damage the surface over time. Nothing else about maintaining the glass changes.

Decide what the evening looks like. Daytime privacy is what reflective and neutral dark films deliver well, and a lit room at night is visible from the street regardless of the product. If a bedroom or a street facing living room needs privacy after dark, that is solved with window coverings or with frosted film on the lower portion of the glass, and it should be settled at specification rather than discovered in November.

Confirm the exterior appearance rules that apply to you. Condo declarations and commercial leases frequently regulate the look of the facade, and reflective film is the category most often restricted. Getting the syndicate or the landlord to approve a sample before the order is placed avoids an expensive removal.

Decide whether you want privacy alone or privacy with solar performance. Reflective privacy films reject a large share of solar heat as a by-product, which on a west or south elevation is worth having. On a north elevation you are paying for performance the exposure will never use.