Roof Truss Blocking

Truss blocking at hip ridge.

Roof truss blocking.

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. It is important however to understand that this blocking creates the structural boundary members for the roof diaphragm and it is not optional. The lay in is good enough. A true stick framed hip is bearing a truss hip not so much.

For trusses with heel heights less than 15 this blocking can be made of solid sawn dimensional lumber as shown in figure 1a. With trusses one truss makes up two planes so it s already tied together on a handstack roof you need that sheeting to tie one plane to the hip and from the hip to another plane. A ledger is a horizontal board that is attached to the top of the the wall. Walls that are constructed of concrete block that need to be covered with a roof will require the use of a ledger.

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. 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 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.