Insulating Open Web Floor Trusses

Insul web helps support them.

Insulating open web floor trusses. All four edges of an open web truss floor assembly require the installation of a sheathing material to enclose the entire floor cavity and then all joints and penetrations need to be air sealed. Open web floor trusses are constructed with 2 x 4 s on top and bottom with a sort of web in between secured with metal plates. Most insulation depots should have them. The open space is ideal for running wires pipes and utilities.

These trusses typically used as joists have diagonal bracing or struts and are made in quebec by open joist triforce. To achieve the 16 inch depth we wanted for insulation and an air space under the sheathing we used open web parallel chord trusses as the rafters. The joists allowed us to reduce the boxes and bulkhead to hide ducting to almost zero with the exception of inside a main floor closet and the main floor powder room. That might be an option but will need to get with the inspector to see if he ll allow it.

These trusses are 20 deep and we re putting r30 insulation in and that only fills about half the depth. Open web joist chase opening. All joints in the sheathing material must be air sealed. It also allowed us to create a basement ceiling with minimal bulkheads except where load bearing beams are installed.

Trim pieces of fiberglass insulation using a utility knife so the pieces fit into joist bays along the rim joist.