If you are deciding whether to frame your house with the tried-and-true lumber or invest in the potentially superior but more expensive LGS, consider the following questions:
- Which material is more durable?
- Which performs better in earthquakes, fires, and floods?
- Which will help me reduce my energy costs?
- Which costs less and is quicker to install?
- Which of the factors above is most important to me?
These key decision-making factors are outlined below.
1. Wood Durability
Wood’s durability comes from an ability to match its moisture content to that of ambient air. Even soaked with water, wood can still dry with no issues as long as the water drains. This capacity to absorb and release moisture allows wood to perform well in climates with high relative humidity.
Though it’s able to release moisture in the right conditions, wood can suffer severe damage if water soaks it for a long time. Mold can form and spread, causing the wood to rot. Recent tragedies in Berkeley and Folsom are prime examples of structural damage that comes from wood members’ sustained exposure to moisture.
Termites are another foe of wooden structures. Wood’s cellulose content attracts the subterranean pests, and once they get inside a home through various crevices, they attack any wooden item in their path. United States Department of Agriculture (USDA) estimates that termites cause more than $2 billion worth of property damage every year.
Despite these weaknesses, wood frames can last a long time. Take the Fairbanks House, for example. Built in Massachusetts around 1641, the house still stands, and is the oldest wood frame building in the United States. Many homes built with the now-obsolete balloon frame in the late 19th century are still around today as well.
In terms of durability, steel has an upper hand over wood. Steel’s inorganic nature protects it from mold, rot, and vermin. Being non-porous, steel cannot accumulate water and does not suffer from moisture-related warping, shrinking or cracking. That said, exposure to water and salt air can lead to corrosion in LGS members, and must be countered with appropriate anti-corrosion measures.
2. Seismic Performance
Wood is a sturdy material, and under normal circumstances a wood frame transfers vertical loads down the studs to the concrete foundation beneath. When an earthquake strikes, horizontal loads begin to act on the structure; to prevent collapse, it must be braced with adequate lateral reinforcements. Lateral bracing may be achieved by attaching wood structural panels attached to the frame to form shear walls, and other options are available, including prefabricated shear walls.
Steel’s flexibility in design is a major advantage when it comes to lateral load resistance. Where wood frames’ seismic bracing options are generally limited to shear walls, LGS frames afford engineers multiple alternatives. These include flat-strap X-bracing, plywood and steel sheathing.
3. Wood Fire Resistance
Nowadays, pine, fir, and spruce are the tree species of choice in wood frame construction. Cheap and light, these species are budget-friendly and easy to handle during installation. Unfortunately, their soft wood ignites quickly and spreads flames faster than the heavy hardwoods once popular in timber framing.
To prevent wooden structures from burning, fire-resistant materials such as fire-rated gypsum wallboard must be incorporated into the design, along with sprinkler systems, adequate exits and egress routes.
Steel’s inflammability acts as a barrier to the spread of flames, an important safety feature lacking in wooden frames.
Although it does not burn, steel does begin to lose strength once exposed to temperatures over 550°F. Residential house fires hover around 1,100°F, at which temperature steel retains only 50% of its normal yield strength. Without proper protection, the steel frame will buckle and collapse. To prevent this scenario, fire-resistant materials must be used to guard the frame from direct exposure to flames.
Because wood develops mold, rots, warps, and shrinks when soaked in water for a long time, flood-resistant measures should be used when building in areas susceptible to flooding. Applying water-repellent paint to the frame, using Expanded Polystyrene (XPS) insulation boards, and spraying high-density closed-cell foam into stud bays are all effective measures for preventing or reducing flood damage to the building’s wooden frame.
Galvanized steel has a protective zinc coating, which acts as a moisture barrier. This coating gives galvanized steel a definitive advantage over wood, by making it almost invincible in flood conditions.
The caveat is that the quality of protection that galvanization offers depends on the coating thickness and the environmental conditions. Galvanized steel exposed to salt air, acids, strong alkalis, and prolonged submersion in water may lose its zinc coating over time and begin to corrode. In such adverse environments, steel’s longevity may benefit from anti-corrosion coatings applied on top of the zinc coating.
5. Energy Efficiency
Thermal Bridging is a process by which heat escapes an enclosed space through a material that bypasses insulation.
Steel’s chemical properties make it an excellent thermal bridge. Its electrons move around freely, and when they gain energy through exposure to heat, they begin to vibrate quickly and pass the energy to the adjacent electrons.
Steel transfers heat at a much higher rate than wood and sharply reduces a wall’s overall R-value without additional insulation and specialized assembly design.
To prevent heat loss in a light gauge steel wall assembly, a rigid insulation board along with drywall should be placed on the studs’ exterior side. This keeps the studs on the warm side of the insulation and prevents heat from escaping.
Meeting prescriptive R-value requirements is much easier with a wood frame, thanks to wood’s non-conductive nature. Since heat transfer depends on molecules vibrating and bumping into each other, porous materials, including wood, are poor conductors of heat. In a typical wood frame assembly, there is no need to insulate the frame of the building.
Lumber’s low cost is the primary reason that makes wood framing popular in spite of all its flaws.
In a study performed by the U.S. Department of Housing and Urban Development, three pairs of houses were constructed. Each pair was identical except for the framing material – one house had a wood frame, the other had a light gauge steel frame. The study concluded that the cost of the steel-framed home was 14.7% more than that of the wood-framed house. The experiment did not factor in the additional insulation needed for the steel frame.
Time is money, and the length of a project’s schedule may have a direct financial impact on both the owner and the builder. Despite many claims that steel gets installed faster than lumber, one must consider all the variables that affect installation times before accepting such statements as fact.
One of these variables is the installer’s familiarity with LGS framing, as unskilled framers may take longer to complete their phase of the project. Currently, steel lacks popularity in single-family residential framing and not all home builders have the experience of working with it. As well, despite being lighter and requiring less in situ preparation, steel has unpredictable lead times that depend on availability and the intricacy of the design.
As a framing material, LGS outperforms lumber in many respects. It doesn’t develop mold, rot, or get pulverized by termites the same way lumber does. Steel’s strength and design versatility make it an excellent framing material in areas prone to seismic activity, and its superb durability protects steel from flood damage. Despite costing more, steel’s high strength-to-weight ratio means that studs can be spaced at 24 inches instead of 16, leading to savings in materials and labor.
But steel has its weaknesses too. In fires, its inflammability is arguably offset by the tendency to lose strength and buckle in high temperatures. Because of this property, some fire departments limit their firefighting efforts to the exterior of a building once it’s known that it’s steel-framed.
Steel’s poor performance in resisting heat transfer is yet another flaw that gives the material a bad reputation. It’s often a deal breaker for owners wishing to limit their energy use and those worried about their heating and cooling bills.
Together with higher up-front costs, these factors form a barrier to steel’s acceptance into mainstream residential construction. For now, lumber continues to dominate the market thanks to its low cost, proven durability, and a long history of being the go-to framing material.
How We Can Help
If you are not sure which framing material is more suitable for your project, Design Everest can help. Our engineers can assess your design intentions and propose a cost-effective framing solution.If you are settled on either lumber or LGS as your framing material, our team will collaborate with your architect and all relevant disciplines to furnish a structural design that works with your building.
If you’re ready to discuss your project, call us at (877) 704-5687 for a FREE consultation and quote. We can also connect you with a professional engineer or designer right away for a virtual consultation or virtual on-site!
*Note: The content published above was made in collaboration with members of Design Everest.