Rafter Spacing Blocking Placement for Load Support of 25mm Polycarbonate

Rafter Spacing Blocking Placement for Load Support of 25mm Polycarbonate

Blocking is framing member that fits between rafters or studs.
Purlins sit on top of rafters, run perpendicular.

Rafter spacing & blocking placement for poly. See Structural Load, Info on snow & wind.
See Polycarbonate Position & Attach for mid-sheet attachment of roof & wall sheets.

Thickness
Rafter
Spacing
80 lb.
load
105 lb.
load
16mm X-wall
49″
every
3.5 ft.
every
2.5 ft.
16mm X-wall
 24 1/2″
not
needed
every
4.5 ft.
25mm X-wall
49″
every
4.25 ft.
every
4 ft.
25mm X-wall
 24 1/2″
not
needed
not
needed

Mfg. specs for selecting sheet thickness, rafter spacing & blocking placement to support load on roof or wall. Load in lbs./sq. ft. Roof slope over 7/12 snow slides off. Spacing may be relaxed. No specs available.

Bldg. dept. has snow & wind load for your area. Supporting load is factor of frame strength and poly. sheet rigidity. Follow chart and poly. will support load.

To allow for movement of condensation past blocking, set blocking 3/8″ back from outer surface of frame, see Blocking. When using 49″on-center rafter spacing, a neoprene spacer is placed at center of blocking. This eliminates bowing of sheet.

Note: The sheet must be supported on all 4 edges with a minimum of 1/2″ of sheet bearing on the frame. When using sheets that have been cut along the width, and no longer have a rib at the edge, position so first rib is supported by a minimum of 1/2″ of frame.

Polycarbonate Greenhouse and Sunroom Building Supplies