This month, we'll conclude this series familiarizing ourselves with all aspects of light gauge metal framing. We'll discuss the overall green aspects of LGMF, look at some other considerations and make some recommendations based on what we've learned.

Green aspects

At the beginning of 2004, in a three-part series, "LEED: Leading the Way," we took an in-depth look at the green building rating system sponsored by the United States Green Building Council that is changing the way America and the world builds: Leadership in Energy & Environmental Design. We saw that credits/points were awarded in six distinct categories:

• Materials and resources

• Energy and atmosphere

• Indoor environmental quality

• Water efficiency

• Sustainable sites

• Innovation and design

It is in the categories of MR, IEQ and EA that LGMF demonstrates its positive environmental characteristics. Since it far exceeds the 5 and 10 percent goals for recycled content (LGMF contains a minimum of 25 percent and up to 100-percent recycled content), use of LGMF qualifies to receive LEED points under credits 4.1 and 4.2 (LEED v.2.1). As we saw in part two, the modern electric arc furnace method is the primary manufacturing process for making the large coils of steel that are transformed into LGMF cold-rolled shapes. Up to 100-percent recycled material can be utilized with the EAF method for manufacturing steel.

The main goals of the green building movement are twofold:

• Reduce negative environmental (earth/atmosphere) impacts.

• Minimize/eliminate negative health (human) impacts caused by the built environment.

LGMF contributes significantly to this cause by its inherent high-recycled content/recyclability. Recycling means raw materials need not be extracted from the earth, thus preventing harmful eco-disruption (i.e. open-pit mining/clear-cut forests). Recycling also means far less energy is required to produce a finished product. Therefore, recycled products have lower embodied energy-the measure of the energy required to produce a finished product.

Also, LGMF is inert, thus it does not contribute to indoor air pollution in any way. This makes it very desirable from an indoor air/environmental quality perspective. Roof ventilators, borrowed lighting, underground air-cooling chambers-such features were incorporated into buildings as far back as the 1800s (i.e. London's Crystal Palace). Today, it is the integration of environmentally sustainable/responsible materials and systems that makes the green building movement so dynamic. LGMF is an important part of this integration.

Pricing

Though domestic steel prices have been experiencing an upsurge in recent years, it is an increase in demand overseas that has caused this situation. Normally, steel prices are very stable due to the high-recycled content and efficient manufacturing processes of the steel industry. Rather, it is the building boom in parts of Asia-China in particular (which is undergoing a major building boom)-that is causing artificially high steel prices domestically due to exports. Thinner gauge than "hot-rolled" structural steel and the omnipresent supply of scrap steel serves to keep LGMF prices stable and competitive with lumber.

In recent years and in some areas in particular, lumber prices have been highly volatile while the overall quality of framing lumber has diminished-LGMF quality is consistently superb due to precision manufacturing standards. Dimensionally stable, straight and without the scourge of warps, twists and shrinkage, the waste factor due to unusable material for LGMF is a fraction of what it is for dimensional lumber.

IEQ and LGMF

LGMF is made from steel and coated with zinc-these metals are inert, they will not off-gas any volatile organic compounds. Most softwood framing lumber is made from southern pine. The distinctive odor of pine is derived from the release of terpenes-pine is the same source of turpentine. Though most people are unaffected by terpenes and even enjoy the smell of pine, other chemically sensitive people may be hypersensitive to the strong odor of pine. A condition known as multiple chemical sensitivity describes people with such sensitivity.

Biologically, we are all individuals and have different tolerances and sensitivities. Fatigue, headaches, nausea, allergic reactions, etc., can result from exposure to certain chemical compounds. In particular, the use of synthetic materials in modern construction aggravates this sensitivity for many people. A study showed that up to 50 percent of all illnesses can be tracked back to the indoor environments we live and work in. That's not surprising considering that the indoor environment typically contains five to 10 times more pollutants than the outdoor environment and at levels of concentration up to 100 times greater.

Another concern is the treatment of framing lumber with Termiticides, such as Borate, and the potential for off gassing into the indoor environment. Nowadays, "healthy house" builders use LGMF for the interior non-bearing walls of a house to avoid entirely the potential problems aforementioned. Another innovation is the use of foil-backed gypsum board throughout, not only on exterior walls as a vapor barrier. The foil backing provides a very effective vapor retarder preventing any off gassing that occurs within a wall cavity from entering the indoor environment. Sometimes, LGMF is given a protective light coating of oil. This coating is easily wiped off prior to installation.

Adaptability

Though it takes some getting used to, it is a fairly easy transition for wood framers to make the switch to LGMF. Industry training programs such as those offered by the Steel Framing Alliance and innovations in tool and fastener design, equipment and a growing acceptance industry wide have made the transition to LGMF a smooth one. In fact, LGMF has been used for commercial interiors for many years thus there's a familiarity with LGMF for many in the field. Price stability and perceived environmental advantages of LGMF over wood make it appealing to all concerned, but for the framer it is the piece-by-piece substitution of LGMF for wood: studs, joists, rafters, etc., that holds the highest appeal. Add on the superior quality of LGMF due to the manufacturing processes' exacting specifications, lightweight, dimensional stability, straightness, mechanical attachment methods and lack of defects such as twists, warps, knots, etc. (commonplace in building lumber), LGMF is very often preferred by framers with experience in both "stick-built" wood and LGMF structures.

About a year ago, an old wood frame house in my neighborhood burned down to the ground. Recently, I was taking my daughter for a walk and passed by the house. I noticed it was in the process of being rebuilt with LGMF. I thought to myself that it is a smart move.

Recommendations:

• Hybrid framing configurations that make the best use of both building lumber and LGMF are a viable option.

• Use full-width thermal batts and framing at 24 inches o.c. for exterior wall applications. Wider spacing reduces the thermal bridging effect and full-width batts ensure the cavity between C-studs is filled completely.

• Strapping placed over the exposed flanges of C-studs at exterior walls helps negate thermal bridging. Strips of plywood ripped to size or felt building paper work well.

• Do not use metal fasteners for foam sheathing (will short-circuit insulation). Place wood strapping on stud flange and connect sheathing to that.

• Consider pre-engineered panels as an alternative to stick-built. Such panels often use less material by spacing members at 32 inches o.c. rather than standard 24 inches o.c. minimum.

• Beware of preservative treated wood/LGMF interfaces and the potential for corrosion. Eliminate or separate treated wood in contact with LGMF and metal fasteners.

• Beware of galvanized/stainless steel contact. Electrolytic reaction between the two metals will cause corrosion.

• Never use a torch to cut LGMF.

• Make sure all fasteners are properly selected and installed.

• Trusses made from LGMF should not have punch-outs.

• Contact the SFA for more information about LGMF:

www.steelframingalliance.com.