A little bounce as you walk around in big room isn’t just annoying, it indicates the floor system is either undersized for the span or was never designed with your comfort in mind. If you’re building or remodeling, you want to feel like the floor is solid and a part of the house. When getting the structure right, stiffness matter more than raw strength.
That means floors is both stable and quiet when built on deeper engineered trusses as the chart above illustrates. Instead of relying on guesswork (standard lumber), this guide relies on precision of engineered. But why does it matter? The depth of truss makes all the difference.
Why Truss Depth Matters for Solid Floors
While a shallow twelve inch truss may work fine spanning eighteen feet, it doesn’t if pushed out further. As the visual layout explains, by adding depth, you can achieve very long clear spans without additional support walls. With open-web trusses, you’re able to span up to twenty-five or even thirty feet in between support. And that’s what enables the spacious floor plans found in today’s homes. Distance is gained through height, a simple trade-off.
Why do builders sticks to sixteen inches on center? Because that happens to coincide with size of standard sheet goods, whether those are OSB, or plywood (used as subflooring). Sixteen inches is path of least resistance, resulting in less wasted material. To keep things rigid over longer spans, such as when approaching the twenty-four-foot mark, you may require a deeper truss: eighteen or twenty inches. Why? The graphic explains this clearly, as a twenty-four inch depth can span thirty-six feet over longer distances. This give you the space for more design freedom (and fewer interior wall).
Also pay attention to the load rating. Because a kitchen loaded down with appliances doesn’t bear same stress as a bedroom, and your home gym bears different stresses then other rooms… Residential floors are not all alike. And while common live load is 40 lbs/sq ft +10lbs dead load, there is an allowance for this in the reference guide. But if you’re going to put a jacuzzi tub in that bathroom, or keep some exercise equipment on second story, the loads increase and shorter spans supports less weight.
Sure, the house supports the drywall so you think it’s okay, but remember deflection limits determine what is comfortable. Usually, deflection limit is limited to 1/360th of the span (bouncier than that is just plain wrong). The utility routing is also best based off an open web design.
The massive open area allows plumbing, duct work, and electrical to be fed right through the open space instead of having to cut into the chords. Installation takes hours less time and there is no chance of accidentally punching a nail through one of these wires when installing flooring later. Trusses don’t lose their strength when you drill holes in them, unlike solid joists which will eventually weaken from each hole drilled.
Truss flexing is why following the bracing instructions is necessary before sheathing them and blocking them up. While under construction, temporary braces holds the trusses vertical. Permanent strong backs and blocking align them over time. Depth is where people gets it. They look at a thick piece of lumber and think it should of been stronger. That’s mostly psychology, as engineering is more about connection points and how well material spreads loads than just its thickness.
Always have your final plans stamped by an engineer who knows your local code requirements and knows the condition of your soil. While this is a starting point for discussion, different regions and design intent mean specific loads can vary. Whether you’re adding on an old rickety porch or chasing a wide-open great room, knowing how depth relates to span will keep you from costly callbacks.
Having solid floors makes a house feel like it’s built to last. This confidence starts with making good structural choices before laying down hardwood.
