The Role of Spacers in Double-Pane Windows

Bob Sheehan

By virtue of their design, double-pane windows are effective at reducing energy loss, increasing thermal comfort, and minimizing noise in your home.

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image credit: big stock

A big part of their functionality, however, depends on the spacer that separates the two panes of glass. Spacers are bonded to the glass panes with seals and help create an airtight cavity within the glazings. They are coated with a desiccant to soak up any moisture that gets in and curb condensation inside the cavity. They also manage stress brought about by changes in temperature and pressure.

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image credit: big stock


That said, this little accessory holding your window panes together plays a very important role and must therefore be chosen carefully. The wrong spacer can radically reduce the functionality and energy-efficiency of your double-pane windows and keep you from maximizing their benefits.

image credit: big stock

Types of Window Spacers

One of the most common types of materials used for spacers is metal. Metal spacers are hollow and commonly made of aluminum, stainless steel, or galvanized steel. They come in two types of systems:

  • Single-seal. Single-seal systems have spacers bonded to the window panes with an organic sealant that counters moisture penetration. The downside is that these systems don’t provide a very effective seal for low-conductance gases.
  • Double-seal. These systems use primary and secondary sealants around the metal spacer. The first sealant controls moisture and gas loss, while the second adds structural strength to the window system.

The problem with metal spacers is their high thermal conductivity, which reduces the energy-saving benefits of multiple panes, gas fills, and insulating frames. Nonmetal spacers provide better thermal performance and are available in three types:

  • Composite. Composite spacers feature several components, which may include highly insulating plastics, flexible stabilizers, desiccated coatings, and moisture barriers.
  • Structural foam. These spacers are usually made of EPDM or silicone foam. Like composite spacers, they are also equipped for condensation reduction and protection against moisture infiltration.
  • Thermoplastic. Thermoplastic spacers are different in that they are extruded directly between the glazings. The primary material is a synthetic rubber called polyisobutylene (PIB) with an integrated desiccant.

Besides the use of low-conductivity materials, window manufacturers have also developed new approaches to further improve spacers’ performance. These include:

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  • U-shaped design. Spacers with U-shaped profiles are better equipped for fluctuations in temperature. The design also reduces stress on the sealant, providing more effective bonding and structural support.
  • Warm Edge Technology (WET). Warm edge technology extends the thermal effect of the spacer beyond its size, which has a positive impact on the window system’s overall thermal rating. This also reduces the potential for condensation, mold growth, and frame deterioration.

Because a spacer contributes so much to the efficiency of a window, it also affects the efficiency of the building envelope by extension. This is why factors like the type of sealant used, the width of the spacer system, and the thickness of the primary sealant matter when you’re choosing windows. For best results, always check windows’ NFRC labels and talk to your window replacement contractor about the best products for your needs.

Author bio:

Bob Sheehan is a professional contractor and the owner of Renewal by Andersen of Oklahoma. His greatest strengths are his creativity, drive and leadership. He thrives on challenges, particularly those that expand the company’s reach. He is very passionate about what he does and loves to share his experiences to other people.