John Shafer: Today’s Structures: Airtight and Plastics Galore

By Captain John Shafer

Most people are aware that homes built in the past 15 to 20 years have made some attempt to be energy efficient and are more airtight than their predecessors. However, today’s fire environment has been in the making since at least the early 1970s. Many things and events have changed the structures of today; the greatest catalyst was the energy crisis of the 1970s. Overnight, Americans became environmentally conscious of the amount of energy they used and looked for ways to reduce energy consumption and to make changes to the buildings to make them more energy efficient. Government initiatives and code requirements have taken many different paths; but, in the end, it is all about saving energy.  

In addition to lowering energy bills, energy codes can reduce energy load growth and the need for new energy-generation capacity while limiting air pollution and greenhouse gas emissions.   Recognizing these benefits, a majority of states have adopted building energy codes in some form for residential and commercial construction.

Most firefighters are aware of truss lightweight construction behavior in fire conditions, and if you ask any firefighter what has changed in today’s built environment, every one of them will tell you, “Plastics.” The reality is that the plastics-related changes go much deeper than this standard generic answer might suggest–even to the point that sometimes even the structural elements that hold the building up are partially made of plastics.

As mentioned before, the changes that started in the 1970s energy crisis have led to many of the practices that make today’s structure envelope airtight. These changes are evident in many ways.

Modern energy-efficient structures such as structural insulated panels (SIP) and insulated concrete forms (ICF) are unique types of modern structures that present several challenges when compared with the typical type V wood-frame structure. The panels in both of these types of structures are load bearing and not a normal point-to-point load transmission of structural hierarchy.

The SIP is are a composite structural panel with an insulated core of rigid foam, usually polystyrene or polyurethane, and structural facings, most commonly made of 7/16-inch-thick oriented strand board (OSB). SIP homes can have up to 90 percent less air leakage and save up to 40 percent more energy than traditional stick-frame structures.

ICF is a system of plastic foam formwork for reinforced concrete that stays in place as a permanent interior and exterior substrate for walls, floors, and roofs. The forms are interlocking modular units that are dry-stacked (without mortar) and filled with concrete. The forms lock together somewhat like Lego® bricks and serve to create a form for the building’s structural walls or floors. These types of construction are just two of the many energy-efficient changes that have occurred in structural components.

Almost every home built in the past five to 10 years are enclosed in house wraps that can be made of a variety of materials that can work as water vapor and air barriers, making homes more airtight. This impacts fires by keeping temperatures inside and outside as well. In addition, the windows make the buildings energy efficient.  In the past, windows were usually the first thing to fail in a fire, and fire would be showing from the windows when we arrived on the fireground. In contrast, today’s thermal-pane windows can have three layers and sometimes be the last thing to fail. This makes the fire eventually become ventilation controlled because the fire consumed the available air and no fire can be seen because the windows stay intact. We may not realize the structure is full of fuel- rich smoke that only needs air to flash over.

Increased insulation is by far the greatest factor in making today’s structures airtight and energy efficient. Insulation is nothing new; it was part of structures of the past; however, the major difference in modern insulation is the insulation contains foam plastics. In modern residential structure construction, there is a major push to use less wood and more insulation simply because several types of insulation can be used that that can increase the R value (an insulating material’s resistance to conductive heat flow is measured or rated in terms of its thermal resistance or R value), whereas wood’s thermal resistance cannot be increased. Builders can increase the R value in a home without changing the method of construction is to use rigid foam.  Many new state and local codes are allowing more rigid foam to meet national energy initiatives, such as the Environmental Protection Agency Energy Star requirements. Whereas this increase is great for the homeowner’s budget, the foam is increasing the flammable fuel load in the building envelope, which can shorten the time to flashover and enable the buildings to burn faster.

There has been a steady change in the building construction and household contents since the 1970 energy crisis. These changes have been influenced by groups and causes such as global warming; go green initiatives; and federal, state, and local energy codes.

Bio

John Shafer is a 22-year veteran of the fire service and a captain and the training officer for the Greencastle (IN) Fire Department. He instructs in building construction, fireground search, and command management. He is a technical panel member for Underwriters Laboratories (UL) in Chicago for current fire service testing. He is also the Indiana Homeland Security District 7 fire training coordinator. He has served as an adviser to the Indiana Department of Homeland Security for the state’s development of its Fire Training System and assisted with the development of the District 7 Training Council and the District 7 Response Task Force. He manages the social networking site Green Building Construction for the Fire Service on Facebook. He is the owner/writer for Green Maltese LLC and co-owner of Fire Training Toolbox.com.

 

 

 

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