Essential Guide to Light-gauge Steel Trusses vs. Joists in Floor Systems for Multi-family & Hotel Construction

When building multi-family or hotel/hospitality type construction using light-gauge steel, developers pick between Steel Trusses vs Joists as a critical support system. Each of these options have their pros and cons depending on your target application.

General Comparison Table

Feature	Steel Joists (C-joists)	Steel Trusses (Open-Web)
Design	Solid, C-shaped cold-formed sections	Open-web triangulated or ladder-style
Span Capacity	~10–28 ft typical	~20–40+ ft
Weight	Lightweight (1.5-2 LB/SF)	Slightly heavier (2-2.5 LB/SF)
Depth	Shallower (8″–14″)	Deeper (typically 12″–20″+)
MEP Routing	Web punch-outs or soffits needed	Easy MEP pass-through via open web
Cost	$2.5-$3/SF	$6-$7/SF
Labor/Installation	Simple, can be field cut (Labor cost is $3.25/SF)	Prefabricated, faster install if planned well (Labor cost is $2.5/SF) plus crane rental
Lead Time	Readily available, less pre-planning	Custom-fabricated, longer lead time
Fire/Sound Rating	Needs topping or layers for STC/FSC	Often better composite floor pairings
Deflection/Stiffness	More deflection under load	Stiffer due to triangulated geometry
Modularity	Compact and sturdy, ideal for penalization, prefab, & volumetric modular	Primarily used in job-site installation

General Design of Steel Trusses vs Joists

Joists are made of a slightly higher gauge C-stud while trusses are made up of a bottom cord and a top cord with several webs in-between. There are a few types of specialty joists like Superjoists which have a characteristic patented design with large punch outs for MEPs. The total structural depth is shallower at (8″–14″) with a ideal span of 10–28 ft typically speaking.

Floor trusses are made of a top cord and bottom cord with internal crossing members known as webs. The total structural depth is typically (16″–24″ or even 3″+). They can easily span 20–40+ ft. There are also several types of trusses. The primary option we use for floors is called Advant, which is a highly efficient design style.

Steel Trusses vs Joists: Span Capacity

Joists: The key principle is that joists are primarily utilized in shorter spans (anything less than 25′ typically). While trusses can span up to 40′ effectively. The table below is from a hotel constructed by US Frame Factory. Notice how 10″ 12 gauge studs (1000S250-97) are used to span 22′-8″ runs. A shallower 8″ 16 gauge stud (800S200-54) is used to up to 10′-10″.

Trusses: The first thing to understand is that trusses are custom designed per project and depend on multiple factors such as the skill of the designer, floor loads, etc. See below for a 30′ span truss that is 18″ deep with 20 cords. 40′ can easily be reached with a slightly deeper truss (24″). There are a few ways to increase truss span:

• Increase the gauge(thickness) of top cords or bottom cords
• Increase the number of webs
• Increase truss depth (18″ to 24″ for example)

Ultimately its up to the truss designers to make the ideal modifications and optimize the truss. Optimizing for the weight of the metal is always the best route to take.

MEP Routing – Mechanical, Electrical, and Plumbing

It’s easier to route MEP through open-web trusses than through solid joists because trusses are designed with large, open triangular spaces between their top and bottom chords. These open areas allow ducts, pipes, and conduits to pass through the depth of the floor system without drilling or notching structural members. Light-gauge C-shaped steel joists typically have a small holes which water pipes and sprinkler systems can be run. Its impossible to run HVAC ducts through these holes. Fur down and drop ceilings are necessary to accommodate ducting in these scenarios.

Cost Comparison: LGS Joists vs LGS Trusses

Light gauge steel joist are almost always going to be cheaper than trusses. You can build a LGS joist floor system for about $2.5-$3.5/SF or cheaper while a Light-gauge steel truss floor system will run you at least $6-$7/SF of coverage area. The major disadvantage of joists is that the engineer must optimize and span size, resulting in more load bearing walls to frame. Other factors slightly drive up the price of joists (like drop ceiling installation) but from a larger project perspective, it’s almost always cheaper to build with joists. Trusses, while more expensive, can span farther and accommodate HVAC lines easily.

Suitable Floor Systems: Joists vs Trusses

Use a general rule of Thumb

• Use joists → When spans are shorter, budget is tight, and floor depth needs to be minimal.
• Use trusses → When you need long spans, large open spaces, or easy MEP integration.

Below is an example of a perfect layout for joists. Smaller rooms where the joists only have to span 14′. The HVAC cooling and heating is supplied by a wall unit, so you only need drop ceilings in the bathroom for an air exhaust fan which is piped through the center hallway. Examples of these floor layouts can be found in Hampton Inns, Holiday Inns, Tru by Hilton, Towneplace Suites, etc. These general guidelines apply for almost any layout with repetitive narrow rooms.

Below is an example of a apartment layout that needs trusses. There are larger unit rooms that cannot be served by a wall AC unit and central cooling/heating is necessary. The free span here is about 35′ which would be very costly to do with a joist. The depth of truss here is 16″. HVAC layout and open span are the two biggest factors when selecting between trusses and joists.

Labor Costs & Installation

Joists, while being lighter and smaller, are more costly to install because there are serval connection points. On average in the southern US they will cost $3.25/SF. Contractors often just rent a telescopic handler to place the joists on the top floor then two or three men can distribute them into place. Trusses are flown and set using a crane. Labor comes out to about $2.5/SF plus the cost of crane rental.

Minimizing Vibrations

Reducing vibrations in joist or truss floor systems is important for several reasons. A bouncy floor can feel unstable and uncomfortable, even when it’s structurally sound, which affects occupant comfort and confidence. Vibrations also transmit noise through the structure, making footsteps and impacts more noticeable. Over time, excessive movement can damage finishes, causing cracked tile, popped drywall joints, or loose fasteners. Even when a floor meets building codes for strength and deflection, controlling vibration is essential for usability and overall satisfaction. There are few methods for concerned builders to effectively address this issue:

• Use deeper members — taller joists/trusses reduce deflection and vibration amplitude.
• Reduce spacing — closer member spacing (e.g., 12″ o.c. instead of 16″) stiffens the deck.
• Add bridging/blocking — transfers loads between members, spreading vibrations out.
• Use thicker or stronger subfloor — thicker sheathing (e.g., 1 1/8″ vs. 3/4″ plywood or concrete topping) stiffens the diaphragm.
• Adding mass (augmenting with concrete or gypcrete topping) — adds dead load that dampens vibration.
• Resilient underlayment — cork, rubber, or acoustic mats between subfloor and finish.
• Acoustic insulation — dense fiberglass or mineral wool between members.

For steel joists/trusses, the vibration criteria often matters more than the deflection criteria. A floor can meet L/360 deflection but still feel “bouncy.” Increasing stiffness to L/480 or L/600 and adding a concrete topping slab are common fixes in light-gauge steel construction.

Total Floor Assemblies

The three floor assemblies we currently recommend are:

• Dragon Board (Magnesium Oxide [MgO] panels
• 9/16 Decking with 2″ of concrete decking on top of it
• 3/4 Plywood with a leveling compound
  

1. ¾” thick flooring system designated “DragonBoard”
2. Cold-Formed Steel Joist or Truss
3. Joist Bridging (not shown)
4. Clip Angles (not shown)
5. 3 ½” glass fiber batt insulation
6. Resilient metal channels spaced 12” o.c.
7. 2 layers of ⅝” gypsum board on ceiling side

1. 2″ deep concrete with welded-wire fabric
2. Form deck 9/16″ (“B” deck, 20–22 ga)
3. Cold-formed steel open-web trusses or Joists @24″ on center
4. Insulation 6″
5. RC-1 at 24″ on center
6. 2 layers of 5/8″ drywall

1. 1-1/2″ Gypcrete topping
2. 3/4″ Plywood Subfloor
3. Prefabricated Steel Trusses
4. R-30 Full Cavity Batt Insulation
5. RC-1 Resilient Channels
6. 5/8″ Type X drywall

Additional Resources