There are circumstances when the deflection requirements for a specific structure that utilizes floor trusses as structural members are questioned. This is especially the case when either floor toppings and/or brittle floor coverings are specified or were not included in the specification but are installed after the floor trusses have been installed.  

The current residential and commercial building codes provide minimum design requirements for loads and for deflection of structural floor members, which also apply to floor trusses. The building designer may specify more stringent requirements. 

This research report will focus on manufacturer or trade association deflection requirements for a number of floor topping/covering related products: gypsum floor topping, light-weight concrete topping, ceramic or porcelain floor tile, natural stone flooring (including marble), and composite stone flooring. These are all products where deflection may have an impact on serviceability or appearance. 

Each of these products may have different deflection considerations that should be considered in the overall building design as well as in the design of the floor trusses. There are two types of deflection that must be considered: the deflection of the individual structural members and the deflection of the subfloor material that spans the structural members. Only the deflection of floor trusses is within the scope of this report, although references are made to resources regarding subfloor deflection.