Rafter Layout Base and Cap for Polycarbonate

Rafter Layout:               Next: Determine blocking placement to support the load on your frame.

Poly on vertically rafters. Use spacers if high humidity greenhouse.     Then See Install Details

  Spacer Placement

Spacers allow condensation to move past blocking, rafter frame,  High Humidity Applications

When using nominal 4 ft. on-center spacing.
Outside of structure to center of first or last framing member & Base is 48-1/2″ – if using Corner Trim *
Dimension between Intermediate framing members & Base is 49″ On-Center.
Note: Spacer shown above is 3/8″x1″x1″. One Spacer in middle of 4 ft. sheet, two spaced on 6 ft. sheet.

When using nominal 2 ft. on-center spacing.
Outside of structure to center of first or last Base is 48-1/2″, if using Corner Trim *
Dimension between Intermediate framing members is 24-1/2″ On-Cenrter.
No spacers needed on blocking, but hold back 1/4″ as shown above.

* If sheet to overhang rafter, as it comes down the slope, 1st and last rafter spacing is less, plan for overhang 2-3″
• See Position & Attach for mid-sheet attachment of roof & wall sheets.

Polycarbonate Greenhouse and Sunroom Building Supplies