Deformation of dark PVC windows under the effect of the sun: a thermal problem not to be neglected

PVC windows are widely used in residential construction due to their affordability, energy efficiency, and low maintenance. However, opting for a dark-colored PVC window increases the risk of thermal deformation caused by solar heat absorption. This phenomenon, which is still too often underestimated, can have significant consequences for both the performance and durability of the building envelope.

Why is dark PVC more vulnerable?

Unlike pale shades, dark colors absorb more solar radiation. In direct sunlight, the surface temperature of the window frame can easily exceed 70°C, or even higher in summer.

However, PVC is a thermoplastic material: it expands when heated and returns to its original shape when cooled... up to a certain point. When heating is excessive or prolonged, expansion can lead to:

• Permanent deformation of the profile;

• A warping of the frame or chassis;

• An alteration of air and water tightness;

• Difficulty opening and closing;

• Deterioration of seals and sealed glazing.

Demonstrations on the ground

In the most frequent cases observed:

• The frames bulge outwards due to heat.

• The openings rub or stick, especially in the upper corners.

• Interior moldings come loose due to shrinkage or stress on the fasteners.

• Water leaks appear at the bottom of windows after heavy rain.

Compliance and Responsibilities

The Quebec Construction Code does not prohibit the use of dark PVC windows, but imposes a general obligation of durability and resistance to expected climatic conditions. A manufacturer or installer who supplies a product unsuitable for south-facing exposure, without warning or precaution, could be held liable for a design defect or lack of information.

Dark PVC windows should ideally:

• Integrate thermal and UV stabilizing additives into the resin mix;

• Be reinforced with internal galvanized steel profiles to limit deformation;

• Be installed with appropriate expansion gaps;

• Be accompanied by a technical opinion from the manufacturer validating their installation on facades heavily exposed to the sun.

Professional recommendations

As a building expert, it is relevant to recommend:

• Avoid dark PVC windows on south or south-west facades without sun protection (cap, eaves, etc.);

• To validate with the manufacturer the thermal performance limits of its dark products;

• Inspect warped windows for leaks or structural damage to the adjacent wall;

• To document any premature deformation as a potential hidden defect or manufacturing defect.

Conclusion

While dark PVC windows offer a contemporary aesthetic, their thermal performance can quickly become problematic in the presence of direct sunlight. Sun-induced deformation is a very real, observable, and potentially damaging phenomenon in the medium term. It is essential to carefully assess exposure conditions, product specifications, and installation practices to ensure durable and compliant fenestration.