Roof Diaphragm Blocking

2306 2 4 gypsum board diaphragm ceilings.

Roof diaphragm blocking.

2306 2 3 double diagonally sheathed lumber diaphragms. An unblocked diaphragm has no requirement for blocking between unsupported edges of adjacent panels. Similar changes to 2306 3 for shear walls. Only lumber blocking shall satisfy blocked diaphragm requirements.

The 200 pounds of uplift force allowed by the irc does not take into account the nailing between the trusses the blocking and the top plate when blocking is provided. It also states you could stagger the blocking in a blocked diaphragm allowing vents every other truss bay. I think on a typical residential roof the rafter and certainly the truss is the primary bending resisting member and that the osb sheathing is the diaphragm element as long as rafters and blocking keep the diaphragm from buckling and properly transmit the load components up into the diaphragm. Which a blocked diaphragm can be designed are many times greater than those for diaphragms without blocking.

Since the individual pieces of. Gypsum board diaphragm ceilings shall be in accordance with section 2508 5. If this were framed the way i would typically do it the unblocked but staggered roof diaphragm would have 240 allowable shear where with their method it would be 180. 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.

Apa s diaphragms and shearwalls l350a has a good set of tables showing the strength of various blocked and unblocked sheathing methods. In irc table r602 3 1 at right blocking between roof trusses is required to be fastened to the top plate with three 8d 2 long x 0 113 diameter toe nails. Diaphragm types case 1 diaphragm higher shear values panels perpendicular to floor framing for improved performance cases 2 6 may be preferred for low shear demand where changing framing direction helps hvac runs fire blocking draft stopping n s 4x8 sheathing roof trusses. You then provide double the nailing requirement at the blocked bays.

There is an unquantified load path resistance interaction present. The three major parts of a diaphragm are the web the chords and the connections. For 1 2 inch panel maximum span shall be 24 inches. To roof diaphragm at top and to foundation at bottom roof horizontal diaphragm carries load to end walls.

It is important however to understand that this blocking creates the structural boundary members for the roof diaphragm and it is not optional. Diaphragm and becomes one of the connections from the roof diaphragm to the shear wall.