Insulating Open Web Floor Trusses

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.

Insulating open web floor trusses.

Most insulation depots should have them. These trusses typically used as joists have diagonal bracing or struts and are made in quebec by open joist triforce. 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. 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.

All joints in the sheathing material must 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. These trusses are 20 deep and we re putting r30 insulation in and that only fills about half the depth. The open space is ideal for running wires pipes and utilities.

I have these in my home and i use the space for extra storage as you can see in the picture. That might be an option but will need to get with the inspector to see if he ll allow it. Trim pieces of fiberglass insulation using a utility knife so the pieces fit into joist bays along the rim joist. Any air leakage in an open web floor cavity allows air movement across the entire floor assembly.

Open web joist chase opening.