Roof Truss Blocking

Walls that are constructed of concrete block that need to be covered with a roof will require the use of a ledger.

Roof truss blocking.

The lay in is good enough. A ledger is a horizontal board that is attached to the top of the the wall. A new provision in the 2009 irc and carried through to more recent versions is the use of blocking panels between roof trusses to connect the trusses to the braced wall panels below if the heel height is greater than 9. Tabulated allowable diaphragm lateral design loads contained in the building code are based on testing of unblocked and blocked diaphragms structural wood members used at intermediate sheathing edges to increase the shear load in the diaphragm.

For trusses with heel heights less than 15 this blocking can be made of solid sawn dimensional lumber as shown in figure 1a. The braced wall panel to the top of the rafters or roof trusses above is between 91 4 inches 235 mm and 151 4 inches 387 mm blocking between rafters or roof trusses shall be provided above the braced wall panel in accordance with figure r602 10 8 2 1. A true stick framed hip is bearing a truss hip not so much. It is important however to understand that this blocking creates the structural boundary members for the roof diaphragm and it is not optional.

Roof trusses attach to a ledger that is on top of a block wall. Each block is 2x4 or 2x6 depending on the size of the rafters and is secured to the top plate. Depending on the building codes in your area you may be required to install blocking up the rafter sections towards the hip of the roof a requirement designed to further secure truss systems against lateral movement.