This course is part of the Multifamily Housing Academy

THE ATTRIBUTES OF EXTRUDED ALUMINUM

Aluminum is one of the most specified materials in the residential and commercial buildings construction industry, and no wonder: it’s durable, stiff yet flexible, strong but light, impermeable, and resistant to bugs, rot, and wear. It is also noncombustible and non-toxic and can be endlessly recycled; in fact, recycling rates for aluminum used in the building industry exceed 90 percent.

The most abundant mineral in the earth's crust, aluminum is derived from bauxite, which is mined from the earth. After processing, the resultant alumina undergoes a smelting and alloying process that produces solid logs of cast metal, known as billets, from which extruded aluminum shapes or profiles are made.

Aluminum trim products are made by extruding aluminum alloy through dies to create distinctive profiles. Most extruded shapes for architectural use are fabricated from AA 6063, an aluminum alloy containing magnesium and silicon. Type 6063-T5 Aluminum, commonly referred to as the architectural alloy, has a very smooth surface and is the best alloy suited for anodizing applications. The T5 designation indicates it has been artificially aged and moderately heat-treated; this process is what gives the aluminum its rigidity. Extruded trim products are protected from rust by an oxide film that naturally forms during the extrusion process.

Photo courtesy of Tamlyn

As the final stage of the powder coating process, the oven is where the powder itself will integrate with the aluminum substrate, which will provide a highly durable, long-lasting finish.

Comparing Extruded Aluminum with Other Trim Options

Extruded aluminum trim can work with many common cladding types, including fiber cement panels, lap siding, and even tongue and groove cedar. It is manufactured to integrate with and complement most major siding products, and it can be used on both exteriors and interiors.

Extruded aluminum has several advantages over other common trim options. Aesthetically, it matches the clean, modern look of many contemporary projects, and it can be used strategically to break up flat panel walls with large expanses of cladding, or to add distinctive profiles to corners.

When it comes to durability, extruded aluminum has greater longevity than materials like galvanized steel and polyvinyl chloride (PVC). Thinking about the Life Cycle Cost Analysis framework introduced earlier, let’s compare extruded aluminum with two common trim alternatives.

Galvanized steel has a lower first cost than extruded aluminum, but it is less durable. In addition, installing bare mill galvanized steel and aluminum flashing in direct contact with most claddings will increase the chances of a chemical reaction, which can cause wear and breakdown in both products. Maintenance costs, including potential replacement or major repairs, will likely be higher for galvanized steel than for extruded aluminum, leading to a higher total life cycle cost for the trim or cladding package. And in the meantime, before repair or replacement, the exterior with galvanized trim may show noticeable signs of the damage, reducing the visual appeal of the building.

Polyvinyl chloride, or PVC, is the least expensive trim option; however, it has some drawbacks and limitations. For one, all-vinyl trim is susceptible to swelling and buckling when exposed to direct sunlight. Painting it with dark colors, which are increasingly popular with both architects and developers, may cause the product to warp. PVC absorbs heat, and in hot climates, the trim may experience extreme expansion and contraction, causing it to warp. Over time, paint may blister and peel.

As you have likely concluded, PVC is a classic case of a product with low first cost but a high life cycle cost. Maintenance is likely to be costly, and the product will have to be replaced long before an alternative like extruded aluminum. In fact, one manufacturer, which used to produce PVC trim profiles for fiber cement siding and soffits, has converted these profiles into more durable extruded aluminum.

Moisture Management for Long-Term Value

Water intrusion is a leading cause of damage or deterioration in buildings and can compromise the long-term durability of building components. For this reason, building codes have strict requirements for managing moisture. The joints where trim panels meet, transition points between different materials, and the joints around windows and other openings, are especially vulnerable points of entry for water. Just as they make trim products to integrate specifically with popular cladding options, most trim manufacturers also offer or recommend code-compliant moisture management products that will work best with their products.

Section 1403.2 of the ICC lays out the performance requirements for exterior walls:

1403.2 Weather protection.
Exterior walls shall provide the building with a weather-resistant exterior wall envelope. The exterior wall envelope shall include flashing, as described in Section 1405.4. The exterior wall envelope shall be designed and constructed in such a manner as to prevent the accumulation of water within the wall assembly by providing a water-resistive barrier behind the exterior veneer, as described in Section 1404.2, and a means for draining water that enters the assembly to the exterior. Protection against condensation in the exterior wall assembly shall be provided in accordance with Section 1405.3.

There are two common strategies for mitigating moisture in the building envelope: housewraps and rainscreens. Housewraps that integrate drainage by, for example, including small spacers that separate the cladding from the sheathing, thereby allowing moisture to drain. Such housewraps don’t require any alterations to the exterior building design or add steps to the installation. A rainscreen is an assembly that includes a water-resistive barrier and an element that creates air space immediately behind the cladding. The air space reduces the chances for moisture intrusion through the cladding and ensures that any moisture that does penetrate can drain out before penetrating further.

Extruded Aluminum Trim for Interiors

Typically, walls and ceilings in multifamily projects are finished with drywall and paint, or with some other type of affordable panelized product. Trim is used as baseboard, openings, and transitions between walls and ceilings, or between two material types. It can also be used to house lighting or to mitigate noise. Conventional choices for interior trim are wood (or an engineered wood product such as MDF) and vinyl; however, extruded aluminum can also be used for interior trim applications, and it can enhance multifamily projects by introducing high design to drywall and panelized surfaces at a fraction of the cost of custom designed and fabricated metalwork.

In addition to introducing clean, modern design to interiors, projects benefit from aluminum’s performance benefits and sustainability characteristics. Because of the frequent turnover of occupants, multifamily interiors are subject to more wear and tear than single-family homes; most damage typically occurs when residents are moving in and out, as furniture and other large items ding corners, damage baseboards, and puncture drywall. Repairing or replacing damaged surfaces can be expensive; however, such damage must be addressed to maintain the building’s quality and visual appeal. Here, extruded aluminum shines. This durable material holds up to the challenges of daily use and long-term wear and keeps units and common areas looking fresh and clean.

Thinking again about life cycle costs, extruded aluminum trim will create long-term value for multifamily projects, as it requires less maintenance and will last longer than other trim choices. It is also easy to recycle, which is not the case for vinyl. And as we shall see in the section on sustainability and occupant health, extruded aluminum is also the best choice for both indoor environmental quality and for minimizing the whole life-cycle health and environmental impacts of the project.

Photo courtesy of Tamlyn

Extruded aluminum is an ideal choice for both indoor environmental quality and for minimizing the whole life cycle health and environmental impacts of the project.