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Timber Curtain Wall and Aluminum Curtain Wall: Comparing the Key Differences

Timber curtain wall

We’re often asked by clients or at trade shows which is better between a timber curtain wall vs. aluminum curtain wall. It’s a good question: After all, traditional aluminum curtain walls have been around since the 1930s, while mass timber walls have only been around for 20-30 years.

Timber curtain walls (TCWs) are unmistakable in their look and feel: Rich wood mullions, large glass panes, and an abundance of natural light are some of their hallmarks.

But which is better between a more traditional aluminum curtain wall (ACW) and a timber curtain wall? We answer that question, and more, below.

How Do Timber Curtain Walls Work?

Timber curtain walls are a type of fenestration system that work similarly to aluminum ones in many respects. Vertical structural mullions provide the wall’s primary support for non-load-bearing curtain walls (load-bearing TCWs use load-bearing glass combined with strong mullions).

  • The timber mullions are fabricated to the project’s precise dimensions, then secured to the base aluminum profile and sealed via a mullion gasket.
  • From there, pressure plate gaskets, pressure plates, insulating blocks, and exterior caps (aluminum or wood) are added before the glazing is installed.

Unicel Architectural’s TCWs are assembled at the factory for easy and fast installation at the jobsite. The mullions are made from mass timber, a type of engineered wood that’s incredibly strong.

What is mass timber?

Mass timber is a type of engineered wood manufactured into large pieces that can be easily fit together. Mass timber variants include glue-laminated (glulam), cross-laminated timber (CLT), laminated veneer lumber (LVL), nail-laminated timber (NLT), and dowel-laminated timber (DLT).

Glulam mass timber is generally considered superior because of its strength compared to other variants.

What about height and fire resistance restrictions?

While building code restrictions around wood structures used to be extremely strict, the evolution of building codes in the U.S. and elsewhere (thanks to the strength of mass timber) now allows for much taller wood structures. The 2021 International Building Code (IBC) allows for mass timber structures of up to 18 stories in the U.S.

Mass timber is also fire resistant: A fire resistance test by the Mass Timber Code Coalition showed mass timber outperformed the fire ratings that building codes require.
“What needs to be understood is that, yes, timber burns—but when it burns it actually chars, and the char forms a natural protection against fire,” explains Unicel Architectural’s Samuel Doyon-Bissonnette.

“It’s easy to calculate how much it chars per hour, so if you want to achieve a certain fire resistance, you oversize your beams and columns by a certain amount. It resists and keeps its structural properties for a certain amount of time as the wood chars.”

Beauty and Strength

There’s just something about vast expanses of glass combined with rich wood mullions: From a design perspective, timber curtain walls provide the classic richness and biophilic design elements of wood with the views, natural light, and sleekness inherent in large glass panels.

TCWs can also come in a variety of wood species depending on the design in question, including glue-laminated Douglas fir, black spruce, and white oak.

But TCWs also provide unparalleled strength: Glulam mullions have greater strength and stiffness than steel. When combined with structural glass and glazing and strong silicone adhesive, the result is a load-bearing curtain wall that can allow for glass spans of up to 30 feet.

  • Just like aluminum, the structural capacity of a TCW mullion is limited by its depth: The deeper the mullion, the bigger span is achievable.
  • Unlike aluminum, fabricators aren’t limited in a glulam mullion’s length (other than transport and manipulation reasons).

Timber curtain walls are also much sounder, structurally, than aluminum curtain walls.

Sustainability

The differences between a TCW and ACW from a sustainability perspective are vast. Unlike aluminum, which acts as a thermal bridge by conducting heat and cold, timber is a natural insulator. That means it loses less energy and provides more energy efficiency than an ACW while also providing passive solar heating and better thermal conduction, convection, and radiation management.

Timber is also a renewable resource that, when used in construction, doubles as a carbon storage vehicle (wood is around 50 percent carbon by dry weight).

The creation of aluminum, on the other hand, results in higher carbon emissions and other damaging environmental effects. Here’s a quick sustainability comparison of a timber curtain wall vs. aluminum curtain wall:

  • Aluminum production as a whole emitted around three percent of the world’s direct industrial carbon emissions in 2023.
  • An aluminum curtain wall releases nearly eight times the amount of greenhouse gases (such as carbon dioxide and perfluorocarbons, or PFCs) as a timber curtain wall. This is largely due to extraction (mining), refining, smelting, casting, manufacturing, coating, and maintenance over its lifetime.
    • A timber curtain wall’s lifecycle, meanwhile, includes reforesting and significant carbon storage.
  • An aluminum curtain wall contributes nearly six times more acidification than a timber curtain wall, contributing to soil acidification (which negatively affects vegetation).
  • An aluminum curtain wall contributes nearly seven times more phosphorus pollution, which can severely damage lakes and other water bodies.

A study by Sinha Et al. showed that “the carbon footprint of aluminum window frames is almost 4x higher than that of the wood window frame.”

Thermal Performance

As mentioned above, unlike aluminum, wood mullions have natural insulating capability and don’t conduct heat or cold. This can be combined with high-efficiency glazing including tinted glass, Low-E glass, and other coatings and glass types that improve thermal performance even more.

Their insulating ability and lack of conductivity provide a barrier to the flow of heat and cold, giving TCWs lower U-values than aluminum:

  • Lower U-values provide cooler interiors when it’s hot outside, and the opposite when it’s cold out.

Timber curtain walls also provide better condensation resistance than aluminum (condensation typically appears when warm air meets colder glass) through thermal breaks in the TCW’s framing members. Some aluminum curtain walls can even develop mold if the dew point remains on the interior surface.

There are also no thermal expansion issues with mass timber glulam mullions, which is the case with aluminum.

Ease of Installation

Timber curtain walls are typically precision assembled at an advanced manufacturing facility, allowing for easier, faster, more efficient, and safer installations.

Aluminum curtain walls are also prefabricated, which means there’s little difference between the two in some respects when it comes to ease of installation.

But it’s worth noting that the typical window wall (another type of glass wall) installation requires the coordination of up to six trades in terms of scheduling, quality, design, and execution. TCWs only require one installer, and that’s it.

LEED Contributions

A TCW can better help architects and designers reach Net Zero and LEED goals by potentially satisfying the following LEED prerequisites and credits:

  • Energy and atmosphere prerequisite: Minimum energy performance
  • Energy and atmosphere credit: Optimize energy performance
  • Interior environmental quality credit: Daylight
  • Interior environmental quality credit: Quality views
  • Interior environmental quality credit: Low-emitting materials
  • Materials and resources credit: Building product disclosure and optimization—sourcing of raw materials

Conclusion

While both aluminum and timber curtain walls provide stunning natural light and rich exterior views, it’s clear that timber curtain walls are dramatically superior for a number of reasons:

  • Timber curtain walls are stronger, better at load-bearing use cases, and provide a more sophisticated and rich design element.
  • They’re more sustainable and better for the environment, helping architects reach LEED and other requirements.
  • They offer superior thermal and condensation performance.
  • They’re easier to install than aluminum curtain walls.

Unicel Architectural timber curtain walls have been installed all over the world: From some of the most prestigious universities and hospitals in the U.S., to other public-facing buildings and even private residences.

Contact Unicel Architectural to learn more about how we can help turn your architectural vision into reality.

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