Roof Diaphragm Blocking

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.

Roof diaphragm blocking.

For 1 2 inch panel maximum span shall be 24 inches. The three major parts of a diaphragm are the web the chords and the connections. Similar changes to 2306 3 for shear walls. 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.

Shear forces acting on heel block the building designer may not assume that prescriptive heel blocking will perform adequately as perimeter blocking for the roof diaphragm especially if unsure of the blocking material or how it is being installed. Since the individual pieces of. Diaphragm and becomes one of the connections from the roof diaphragm to the shear wall. Tongue and groove edges panel edge clips one midway between each support except two equally spaced between supports 48 inches on center lumber blocking or other.

An unblocked diaphragm has no requirement for blocking between unsupported edges of adjacent panels. It also states you could stagger the blocking in a blocked diaphragm allowing vents every other truss bay. Only lumber blocking shall satisfy blocked diaphragm requirements. It is important however to understand that this blocking creates the structural boundary members for the roof diaphragm and it is not optional.

Apa s diaphragms and shearwalls l350a has a good set of tables showing the strength of various blocked and unblocked sheathing methods. There is an unquantified load path resistance interaction present. To roof diaphragm at top and to foundation at bottom roof horizontal diaphragm carries load to end walls. 2306 2 4 gypsum board diaphragm ceilings.

Gypsum board diaphragm ceilings shall be in accordance with section 2508 5. Double diagonally sheathed lumber diaphragms shall be designed and constructed in accordance with af pa sdpws. 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. 2306 2 3 double diagonally sheathed lumber diaphragms.

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 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.