Blocking Between Roof Trusses

Blocking or boundary member.

Blocking between roof trusses. 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 for trusses with heel heights less than 15 this blocking can be made of solid sawn dimensional lumber as shown in figure 1a. Each block is 2x4 or 2x6 depending on the size of the rafters and is secured to the top plate. Some may call these wood members blocking and deem them as optional. In my experience traveling across the country observing wood framed construction it was apparent that east of the rocky mountains structural wood members in line with supporting walls between roof framing cease to be installed.

A continuous band rim or header joist or roof truss parallel to the braced wall panels shall be permitted to replace the blocking required by this. Preventing rotation is typically accomplished by installing full depth solid blocking along wall top plates between rafters and ceiling joists. And often in a humid environment. Truss heel blocking can function as perimeter blocking of the roof diaphragm however the adequacy of this connection depends on multiple factors the building designer may not assume that prescriptive heel blocking will perform adequately as perimeter blocking for the roof diaphragm.

As roof pitch is lowered the weight burden on the rafters increases. For instance if your roof has a steep pitch you may be able to use 2 inch by 4 inch rafters but if your roof has a low pitch building code may require that you used 2 inch by 6 inch or 2 inch by 8. For low pitch roofs building codes may require larger dimension rafters. Where required by this section blocking between rafters or roof trusses shall be attached to top plates of braced wall panels and to rafters and roof trusses in accordance with table r602 3 1.

Roof rafters and ceiling joists shall be supported laterally to prevent rotations and lateral displacement when required by section 2306 7.