Open Web Steel Joists
Floor & Roof Structure: MATERIALS ENCYcLOPEDIA
Applications for this system
Roof framing (typically for flat roofs, but can be used for pitched roofs)
Metal top and bottom cords with welded metal webbing
Ratings Chart for open web steel joist floor or roof
The ratings chart shows comparative performance in each criteria category. Click on the tabs below for detailed analysis of each criteria.
- HOW THE SYSTEM WORKS
- ENVIRONMENTAL IMPACTS
- EMBODIED CARBON
- ENERGY EFFICIENCY
- MATERIAL COSTS
- LABOUR INPUT
- SKILL LEVEL REQUIRED
- SOURCING & AVAILABILITY
- CODE COMPLIANCE
- INDOOR AIR QUALITY
- FUTURE DEVELOPMENT
Open web steel joist System
Steel top and bottom cords are welded to steel webbing to create a joist capable of handling the required loads and spans.
Typically, these joists are used horizontally, to create floor decks or flat roof decks. Open web steel joists can be custom-ordered to create pitched roofs, vaults or any other geometry. Flat joists are quite cost competitive with wooden competitors, but custom steel joists can be quite expensive.
Common open web steel joists are intended for use in steel-framed buildings. If you are intending to use these joists as part of a frame with wooden posts and beams, check with the manufacturer of the joists to ensure that proper connections and fastening methods are prescribed.
Environmental Impact Rating
Harvesting — High
The extraction of ore for steel production is a high-intensity process, with impacts including habitat destruction and air and water pollution. Recycled content can mitigate these impacts.
Manufacturing — High
Steel production is a high-intensity process, requiring several applications of high heat, with impacts that include fossil fuel use, air and water pollution. These inputs are equally high for recycling steel. It can be difficult to trace the origins of the raw materials that are contained in a manufactured product like an open web joist.
Transportation — Moderate to High
Sample building uses 4,262.8 kg of steel joists for roof and floor:
6.4 MJ per km by 15 ton truck
4 MJ per km by 35 ton truck
1.07 MJ per km by rail
Manufacturers exist in most regions. It is difficult to ascertain the transportation impacts of the material through the whole production cycle, as steel is a multinational industry.
Installation — Negligible
Recyclable – All metal offcuts
Chart of Embodied energy & carbon
open web steel joist roof:
open web steel joist floor:
Open web steel joists are typically used in scenarios where the beams/joists are inside the building enclosure, so any insulation strategy is usually accomplished on the outside of the joist. As long as the exterior insulation levels are suitable and thermal bridging has been eliminated, the steel joist won’t have any impact on energy efficiency.
Material costs: Low to high
Steel joists for residential construction are not as common as the varieties of wooden options. Steel joists are built to a number of standard sizes, and if a standard size is appropriate then the costs can be quite low. As the joists cannot be modified on site to fit particular spans, custom-sized joists will be fairly expensive.
Labour Input: moderate to High
Where open web steel joists are being used as part of a prefabricated steel frame, the labor input can be fairly low as these complete systems have been well designed and refined to minimize labor time.
If the steel joists are being used in a custom context, the amount of labor required will be determined by the complexity of the design, the type of fastening being used and the amount of site-fabrication required. Having a designer who is knowledgeable in the use of steel joists can help to minimize labor input.
Connections between steel joists and other building elements (wooden frames, wooden floor decks) can require specialized fastening systems that can increase labor times.
Skill level required for homeowners: moderate to high
Specialized professional crews constructing entire steel frames complete most open web steel joist installations. Most regions have many companies with qualified and competent workers offering this service.
Many open web steel joist installations require on-site welding. If this is the case, the homeowner will need to have the skill and equipment to do that work to the satisfaction of local codes.
An owner-builder can install open web steel joists if the installation is quite straightforward, with simple connections to adjacent materials. If the joists require cutting or welding, only those with the proper tools and training should do the work.
Sourcing & availability: Easy
Most regions will have several suppliers of open web steel joists.
Durability: Very High
Open web steel joists should have a long lifespan. Corrosion due to continuous exposure to moisture is the only thing that can limit lifespan, and it should be easy to keep joists dry in a properly built and maintained building. Steel joists will often outlive the service life of the commercial buildings in which they are commonly used.
Open web steel joists are a pre-engineered system, and are an accepted solution in most jurisdictions. Building departments will typically want to be provided with a signed, stamped version of the joist drawings as part of the plan submission.
Indoor air quality
The steel joists themselves will have no detrimental effect on indoor air quality, but the coatings on the steel may. The paints used on the steel are applied at the factory, giving the homeowner little choice in the type of paint used. Steel products are sometimes sprayed with oils to further prevent corrosion. Consultation with the manufacturer or distributor will need to occur to ensure that IAQ will not be detrimentally affected.
It may be possible to coat the steel joists with a healthy paint or sealant on-site to prevent exposure to the factory-applied finishes.
Resources for further research
The steel industry has made strides to lower the energy consumption on the production side, and good recycling programs for steel have been well developed. Major changes in the ingredients or manufacturing processes involved in creating steel joists are unlikely.
Tips for a successful open web steel joist floor or roof
1. Open web steel joists are proprietary products, and each manufacturer will have its own installation guidelines that should be followed closely.
2. Cutting, notching or altering an open web steel joist should only be done in a manner approved by the manufacturer.