During attic renovation and insulation installation, vapor permeable membranes are a crucial element. How are vapor permeable membranes properly installed? While their price is higher than standard “plastic sheeting,” it is by no means a substitute for a vapor barrier. Discover why.
Importance of Vapor Permeable Membranes
Attic renovation typically revolves around the type and quality of insulation and its cost. EPS boards (polystyrene) or mineral wool are often debated on internet forums. The choice between these insulation materials, their cost-effectiveness, and the necessary thickness for satisfactory insulation are common concerns.
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However, the significance of vapor permeable membranes is often overlooked. Their improper installation or neglecting to install them altogether can nullify the effectiveness of even the thickest layer of quality insulation.
Another common mistake is using standard PVC or “plastic sheeting,” which comes with a price during renovations. Here’s why vapor permeable membranes are a crucial factor in attic renovation.
Understanding Vapor Permeable Membranes
Vapor permeable membranes are not the same as standard PVC or “plastic sheeting.” These are quality membranes that allow vapor to pass through, whereas standard PVC blocks both water and vapor. This fundamental difference is critical. In living spaces, including attics, significant moisture is produced (cooking, ironing, showering, drying clothes, etc.).
When warm, moisture-rich air from the living space finds its way into the interior of the roof structure and reaches colder areas, it cools down and releases moisture, leading to condensation—water droplets. This creates several problems: ideal conditions for mold growth and reduced thermal insulation properties if the insulation absorbs water.
That’s why, during attic renovation, insulation material is first laid, followed by a vapor barrier, and then gypsum boards or any other final covering. The membrane acts as a barrier between the moist air in the living space and the insulation.
Proper Installation and Functionality
The direction of vapor permeability is crucial. During installation, ensure that the printed side of the membrane faces the interior space, not the exterior. Vapor permeable membranes control the passage of moisture from the interior to the insulation, preventing sudden vapor transfer from indoor air to the roof structure.
This controlled moisture transfer prevents condensation and moisture buildup within the insulating part of the roof structure. Using standard PVC or “plastic sheeting” purchased from hardware stores and paint shops is not an optimal solution.
These materials completely block vapor passage from indoor spaces to the roof structure, creating a hermetic effect. In such conditions, maintaining optimal indoor humidity levels becomes much more difficult, leading to condensation and dampness issues.
Conclusion
While some may view vapor permeable membranes as optional during installation, experts warn against this perception. When insulating, preventing air leakage is crucial. Simply laying a thick layer of mineral wool or polystyrene without a vapor barrier won’t have the desired effect if air “leakage” occurs.
This is especially noticeable on windy days. Installing high-quality insulation without a vapor permeable membrane can be likened to installing top-of-the-line PVC windows with triple glazing but without sealing strips on the profiles.
Cold air will always find its way to heated spaces, nullifying the positive effects of the quality insulation materials used. Additionally, it’s essential to create a barrier between the insulation—especially if it’s woolen—and the living space to prevent glass or stone wool fibers from entering living areas, which could adversely affect occupants’ health. For this reason, workers wear protective masks and goggles during insulation installation.