Does XPS insulation need a vapour barrier?

Because of its outstanding thermal insulation capabilities and durability, extruded polystyrene (XPS) foam insulation is a popular choice for insulating buildings. However, one frequently asked question is whether XPS requires a vapor barrier. In this post, we will look at the relevance of vapor barriers and whether they are required for XPS insulation.

What is a Vapour Barrier?

Before going into whether XPS insulation requires a vapour barrier, it’s critical to understand what a vapour barrier is and what it’s used for. A vapour barrier is a substance that prevents moisture from flowing through a building’s walls or roof. Moisture can enter a structure in a variety of ways, including from the ground, through roof leaks, and through the walls owing to excessive humidity levels. Moisture may harm the insulation, frame, and other structural components of a structure if it is allowed to enter.

what is vapor barrier

A vapour barrier is often constructed of a moisture-resistant substance, such as plastic sheeting or foil-faced paper. To prevent moisture from entering the building, the vapour barrier is put on the heated side of the insulation. When correctly placed, a vapour barrier may assist decrease the danger of moisture damage while also improving the building’s energy efficiency.

Does XPS Insulation Need a Vapor Barrier?

The answer to whether XPS insulation requires a vapour barrier is complex and relies on the application. The closed-cell structure of XPS makes it moisture resistant, which means it does not absorb water. As a result, XPS insulation is appropriate for usage in high humidity or moisture regions, such as basements and crawl spaces.

While XPS insulation is moisture resistant, it is not impermeable to water vapour. Water vapour can still travel through the insulation, particularly if there are cracks or air leaks. Allowing moisture to collect can result in mould development, structural damage, and decreased energy efficiency.

As a result, when utilising XPS insulation in locations with high humidity or moisture levels, it is suggested to build a vapour barrier. This is especially critical in below-grade applications, such as basement walls and flooring, where moisture can gather. Installing a vapour barrier on the warm side of the insulation can assist keep moisture out of the building while also protecting the insulation from harm.

It’s worth mentioning that XPS insulation may already have a built-in vapour barrier in some circumstances. Some manufacturers make XPS panels that already have a foil facing or other vapour barrier material attached to the insulation. In some circumstances, an extra vapour barrier may not be required.

Because of its superior thermal resistance, moisture resistance, and durability, XPS insulation panels are a popular choice for insulating buildings. Foil-faced XPS insulation panels are one type of XPS panel. In this post, we will define XPS panels with a foil front, as well as their benefits and uses.

What are XPS insulation panels with a foil facing?

XPS insulation panels with foil facings are XPS foam boards with reflective aluminium foil bonded to one or both sides. The foil layer is a thin sheet of aluminium that acts as a radiant barrier, reflecting heat back into the living area rather than absorbing it by the insulation.

XPS insulation foil faced

Polystyrene plastic is melted and extruded into a thick foam substance to create the XPS foam board. This foam substance is then compacted into insulating sheets. XPS insulation’s foam structure offers a strong thermal barrier, making it a popular choice for building insulation.

Benefits of XPS insulation panels with a foil facing

Improved thermal performance: XPS insulation panels with a foil front provide good thermal resistance, assisting in keeping the building warm in the winter and cool in the summer. The reflective foil layer also contributes to the insulation’s R-value, resulting in a more effective thermal barrier.
Vapor barrier: The foil covering of XPS insulation panels serves as a vapour barrier, keeping moisture from entering the insulation and causing structural damage.
Fire resistance: XPS insulation panels with foil facings are highly fire resistant, making them acceptable for use in places where fire safety is a concern.
Durability: Because of the strength and resilience of the polystyrene foam substance, XPS insulation panels are extremely long-lasting. The foil front provides an additional layer of resistance to wear and strain.

Applications of XPS insulation panels with a foil facing

Roof insulation: XPS insulation panels with a foil covering are often used to insulate a building’s roof. The reflective foil layer prevents heat from being absorbed into the insulation, which can cause structural damage to the roof.
Wall insulation: XPS insulation panels with a foil front are appropriate for use in external walls, especially in places with high humidity or where moisture may be an issue.
Under-slab insulation: In under-slab applications, where the insulation is put between the concrete slab and the ground, XPS insulation panels with a foil front are widely employed.
Insulating pipes: Pipes can be insulated using XPS insulation panels with a foil covering, limiting heat loss and lowering energy usage.
Insulating HVAC ducts: XPS insulation panels with a foil front can also be used to insulate HVAC ducts, increasing the efficiency of the heating and cooling system.

Do XPS insulation panels with a foil facing need a vapor barrier?

The foil covering of XPS insulation panels serves as a vapor barrier, keeping moisture from entering the insulation and causing structural damage. As a result, when employing XPS insulating panels with a foil front, no extra vapor barrier is required.

Is it important to seal insulation panel joints with tape?

Insulation panels are made to fit together firmly to create a continuous barrier against heat transmission. Small gaps and cracks can form between the panels, especially as the building settles or shifts over time. These gaps and fractures can allow air and moisture to enter the walls or ceiling, diminishing insulation efficiency and potentially causing damage.

You may assist prevent air leaks and moisture penetration by taping the connections between insulating panels. This can increase the building’s overall energy efficiency and aid to minimise structural damage.

XPS insulation panel tape

What type of tape should be used to seal insulation panel joints?

There are several types of tape that can be used to seal insulation panel joints. The most common types include:

Foil tape: This tape is constructed of aluminium foil and has an adhesive backing. It is frequently used to seal seams in foil-faced insulation panels, such as XPS panels. Foil tape is sturdy and long-lasting, and it is resistant to moisture and heat.
Acrylic tape: This tape is constructed of a strong acrylic adhesive and is commonly used to seal seams in insulation panels without a foil front. Acrylic tape is versatile and easy to use, adhering nicely to a variety of surfaces.
Butyl tape: This tape is constructed of a rubber-like substance and is commonly used to seal connections in insulating panels that are exposed to moisture. Butyl tape is waterproof and resistant to harsh temperatures and weather conditions.

Why is proper sealing of XPS panel joints important?

When XPS panels are installed, the joints between the panels must be sealed to prevent air infiltration and moisture penetration. Properly sealed XPS panel joints can help to:

Improve energy efficiency: Air penetration through gaps between XPS insulation panels can diminish insulation efficacy, leading in increased energy expenses.
Prevent moisture damage: Moisture can enter the crevices between XPS insulation panels, causing water damage, mould development, and structural damage.
Ensure airtightness: Sealing XPS panel joints with tape helps to ensure that the building envelope is airtight. Which can improve indoor air quality and reduce drafts.

Steps to properly seal XPS insulation panel joints with tape:

Step 1: Clean the joints

Before sealing the XPS panel joints, it is important to clean the joints to remove any dust, dirt, or debris. This can be done using a soft-bristled brush or a vacuum cleaner with a soft brush attachment.

Step 2: Apply the tape

To properly seal the XPS panel joints, a high-quality tape should be used. The tape should be particularly built for use with XPS, with strong adhesion and resilience to moisture and temperature fluctuations. The tape should also be wide enough to cover the joint completely.

Tape should be applied to the joint using firm pressure to ensure good adhesion. The tape should be applied over the joint and onto the adjacent panel, covering the joint completely.

Step 3: Seal the edges

To ensure that the joint is properly sealed, it is important to seal the edges of the tape. This can be done by using a silicone sealant or a foam sealant. The sealant should be applied along the edges of the tape, covering the joint completely. The sealant should be allowed to dry completely before the XPS insulation panels are covered with another layer of material.

Step 4: Test for air leaks

After the XPS panel joints have been sealed, it is important to test for air leaks. This can be done using a blower door test, which measures the amount of air that is leaking into the building envelope. If any air leaks are detected, the XPS panel joints should be inspected and resealed if necessary.