Roof trusses are typically spaced 2′ on center for residential and commercial projects. That spacing can be reduced if needed to better support additional truss loads, longer truss spans, or other factors. Also note that structures designed using the IRC are prescriptively required to have trusses spaced two feet or less (R802.10-11).
Agricultural/post frame trusses are spaced much wider, typically 4’-12′, which again can vary. These truss spaces are typically spanned by purlins.
The three most common spacings for “Open-web” or floor trusses are 16″, 19.2″, and 24″ on center. Sometimes the smaller spacing is chosen in an attempt to reduce the floor deflection and vibrations in the floor system. However, some research indicates that this approach is limited in its effectiveness and is better-solved by increasing the floor depth, shortening the span, or modifying how the sheathing is attached to the trusses.
Truss spacing may be constrained by the materials being used to span between trusses. For example, most sheathing comes in 4’x8’ sheets and is best installed with a two-foot staggered layout. This means that having trusses centered every two feet will ensure that there is a convenient truss chord to which the sheathing can be nailed at each end. This is something to keep in mind when considering using a smaller truss spacing in an attempt to achieve lower material costs for the trusses themselves. It could require more work or material during framing and sheathing.
The only way to know for certain what truss spacing can be used is to have your trusses analyzed using your desired spacing. Let Truss Pal run your designs for you and provide you with truss design drawings that will show you what options you have!