The Role of Doorways in Green Buildings

Sustainable building practices have quickly caught on as a core element in the construction industry.

The rush to embrace this new trend has left many building professionals scrambling to understand how a structure can be made more environmentally friendly and better positioned to achieve certification from LEED or other “green” building rating systems. In this effort to attain certification, all building components must be considered, right down to the doors and hardware.

Statistically, doors and hardware constitute less than two percent of the overall cost of a building, but these vital building components can contribute to the development of environmentally friendly structures by lessening the dependence on virgin raw materials, lowering energy consumption and optimizing thermal performance.

Materials

Most green building standards seek to cut back on the use of virgin raw materials and the associated impact created by their extrusion and processing. To achieve this goal, the use of building materials made with high percentages of rapidly renewable or recycled materials is widely encouraged.

Nearly all steel doors, frames and hardware are made with some amount of recycled material, but the exact quantity will be influenced by the steel production method. Integrated mills use blast furnaces to turn iron ore, coke and scrap iron into pig iron which is then injected into a basic oxygen furnace where it is converted to steel. Doors and frames built with steel produced by this method and feature recycled content that typically exceeds the levels targeted by many green building standards. 

Mini-mill steel production relies almost entirely on scrap metal as the raw material. The scrap is melted by electrical current in an electric arc furnace and turned into steel. So instead of mining the earth to feed its furnaces, mini-mills instead mine junkyards for old cars and scrap metal.

Mini-mill operators estimate that 20 doors can be produced from the steel of one scrapped car. In addition, 5,400 BTUs of energy are conserved for every pound of steel recycled. Also, the air pollutants emitted by mini-mills are a fraction of those produced by integrated mills.

Wood doors can also figure into the equation. Green building standards seek to support environmentally responsible forest management by encouraging the use of products—including doors—manufactured with wood certified by the Forest Stewardship Council (FSC).

The FSC sets standards to ensure forestry is practiced in an environmentally responsible, socially beneficial and economically viable way. Any source of wood that seeks FSC certification must undergo a rigorous verification process from an independent, accredited third-party. The certification body examines the source of the wood and tracks the materials from the forest through the entire chain of custody. FSC certified products can be traced back to their original source.

Green building standards also seek to curb depletion of long-cycle renewable materials by encouraging the use of building products made with rapidly renewable materials, generally defined as plants with a maximum ten year planting-to-harvest cycle. Wood doors constructed with agrifiber cores can help address this concern while still offering the same aesthetic and durability properties as wood fiber doors.

Agrifiber core doors can be made from wheat and straw shafts that are the byproduct of normal farm production. Wheat and straw are planted and harvested within a year, easily fitting the rapidly renewable classification. Agrifiber offers the added benefit of being free of urea formaldehyde as well as holding the distinction as one of the few building products with a favorable carbon balance score.

Optimizing Energy Performance

Improving energy efficiency is another goal of green building standards. Again, doorways can help contribute to this effort with thermal break door frames. These specially designed frames are built to enhance the insulating properties of the building envelope.

Thermal break frames feature strategically placed barriers that prevent heat/cold transfer. In cold weather, the frames reduce heat loss and prevent condensation or frost from forming on the interior portion of the frame. The barrier provides a positive thermal break within the frame profile and thereby delivers maximum protection against cold penetration.

R-valued insulated doors can also be used to improve the building envelope thermal performance. Used on exterior openings in conjunction with thermal break frames and good quality weatherstripping, these doors provide optimum control of energy used for building heating or cooling.

Revolving Doors

The greatest energy savings offered by doorways can be achieved with the use of revolving doors.

A study conducted by students at the Massachusetts Institute of Technology (MIT) compared the ability of traditional swinging doors and revolving doors to limit the exchange of air between the inside and outside of a building. As study explains, stack pressure on the inside of the building forces the cooler air through any opening in the building, causing the air conditioning system to work harder to maintain the desired settings.

“The revolving door stops conditioned air from moving freely,” states a recap of the study in an online MIT sustainability journal. “An open swinging door is like letting go of a balloon—the air rushes out of the opening. A revolving door is never open—seals remain in contact with the walls of the doors at all times. Only the air in the chamber with the person going through the door is transferred.”

The study found a swinging door allows eight times as much air exchange as a revolving door. If ingress and egress into a building were limited to revolving doors the school would save nearly $7,500 (US) at one building alone. The reduction in emissions would also be significant, totaling roughly 15 tons of CO2 annually—again, from just one building.

One significant revolving door-related challenge was noted: getting students to change their habits and stop using the nearby swinging door. The study found that only 23% of people entering and leaving the facility went through the revolving door. This is likely a reflection of the convenience features or ease of use for a swinging door. The number of revolving door users increased dramatically—up to 63%—when a sign explaining the energy savings that could be achieved was placed at the building entrance.

The Big Picture

Although they are relatively small in the scope of an entire structure, doors and hardware are a perfect example of why it is important to think holistically when adhering to green building standards. All building components, regardless of their size, should be considered for their potential environmental impact.