Roof trusses are generally made from two materials: timber or steel. In commercial and industrial construction, steel roof trusses are becoming the norm, and their successes in that sector are causing them to gain in popularity in the residential metal building market as well.
As with any building product, there are advantages and disadvantages to building with steel trusses, which means it is to your benefit to perform due diligence so your team can decide which product makes the most sense for the build-out and overall life-expectancy of your upcoming project.
Advantages of using steel roof trusses
All of the advantages of building with steel roof trusses are akin to the benefits of building with steel in general. In addition to meeting stringent green building certification requirements, steel is strong, durable and resistant to the majority of the threats that wood trusses are vulnerable to.
Here are some of the advantages of building with steel trusses, in no particular order.
- High strength-to-weight ratio. Once of the major advantages of steel trusses is their high strength-to-weight ratio. Not only does this make for a stronger product, and one that can withstand heavy wind and snow loads (more on the later), it also allows for roof designs with superior spanning capacities. This is why steel is almost exclusively the choice for builders designing large sporting arenas, warehouses, hangars and so on.
- It is uniform. Unlike timber which can't possibly be uniform due to its inherent, natural growth environment, steel trusses are completely true to form. They are pre-fabricated in factories with stringent quality control. Therefore, the trusses that arrive at the job site are constructed exactly as designed, with minute variation - if any. This isn't possible in the realm of wood timbers, whose properties can vary over time, especially in response to temperature fluctuations and relative humidity.
- Steel is incredibly durable. Adequately coated steel trusses are extremely durable. Not only can they withstand high stress situations under scenarios of both tension and pressure, they also require very minimal maintenance. Steel also has high ductility, so significant deformities can occur - the large majority of which would be obvious and flag a need for replacement - before the roofing system will fail. Steel and metal roof systems are also recommended in areas of the country where there is severe wind and/or or storm potential. Roofs can be engineered to resist extremely high wind uplift ratings, including hurricane-force winds, and the aforementioned resistance to pressure makes them an ideal choice for regions of the country that experience heavy snow-loads.
- Complete pest resistance. Timber trusses are susceptible to pests, which is a serious threat in areas that are prone to termite and other wood-boring pest infestations. While wood can be treated to increase pest -resistance, the treatments are inherently toxic, which diminishes indoor air quality and is a black mark on any project that desires to be sustainable or eco-friendly.
- Fire-resistant. Fire-retardant coatings render steel roof trusses virtually indestructible by fire. This is important for any structure with living occupants or that houses valuable property. Increased fire resistance is also and added benefit for structures built in high-storm areas or where there is a greater risk of seismic activity, both of which can elevate a structure's risk of fire.
- Eco-Friendliness. As mentioned at the beginning, steel and metal buildings get extra points with reputable green building certification programs such as LEED. One of the main reasons for this is that steel trusses are fabricated using up to 90% recycled content and are also 100% recyclable at the end of their lifespan. This, combined with the fact that they are incredibly durable and rarely need to be replace, makes them a very eco-friendly building product.
Many of these advantages segue to other advantages. For example, steel's uniformity makes it less prone to maintenance throughout its lifetime and its ability to be pre-fabricated leads to faster erection times, resulting in lower overall labor costs.
When looked at as a whole, these advantages make steel roof trusses an affordable building option, especially when you weigh the savings gained via lifetime costs as a result of their durability and longevity.
Disadvantages of using steel roof trusses
Of course, no product is perfect, so there are disadvantages as well.
- Vulnerability to corrosion. While steel may be impervious to pests, fire and wind - it is vulnerable to corrosion, particularly as the result of chronic moisture exposure. However, steel trusses purchased from a reputable metal building supplier will be designed and coated in accordance to your climate and building codes. These coatings eliminate the risk of corrosion, assuming the building implements adequate vapor barriers, ventilation and insulation.
- Steel is emissive. Steel quickly emits any heat that is absorbed. This is great news when it comes to products like steel roofing and siding, which mitigate solar heat gain, but it can be a detriment in buildings where interior comfort is important. While steel trusses don't offer the same level of innate insulation that timber trusses do, this too is remedied via adequate radiant barriers and insulation. However, it's important to note that can also increase insulation costs because a greater quantity of insulation is required to fill the attic space.
- Steel can fail at high temperatures. Cold-formed steel cables can fail at 800°F, and steel expands at 1000°F, exerting powerful lateral pressure that can cause walls to collapse. Heat-related truss expansion can also cause the bottom cord to buckle and fail. Thus, fire-proofing steel roof trusses is a must to ensure they will perform well in the event of a fire, keeping in mind that the average residential house fire burns at about 1,100°F (live-safe.org).
- Specialized skills required. Since steel trusses are a relatively new phenomena in the mainstream building arena - particularly in the residential sector - there is a degree of skill required to erect and construct them as per manufacturer's instructions. There are also slightly different tool requirements, and these tools are not typically in the repertoire of the average contractor unless they already work with steel and metal building components on a regular basis. As a result, lack of the proper skills and/or tools can result in either poorly installed trusses or increased labor costs to find a crew that can get the job done right. Similarly, finding experienced metal building laborers may be a challenge if steel buildings aren't the norm in your area.
Because many of the disadvantages of steel roof trusses are mitigated with proactive measures addressed during the design and pre-fabrication phases, many contractors still find steel trusses to be the most advantageous option - especially for large-scale commercial and industrial projects. The key is to buy from the right supplier and make sure the construction team is well versed in the tools and techniques required to construct the building to the design specifications.