Custom Sun Tube

DIY Geodesic Sun Tube Build Guide
West-Facing • Optical Grade

DIY Geodesic Sun Tube Master Plan

Converting an existing 6-inch steel/PVC roof penetration on an F-Domes F75 into a sealed, condensation-proof natural lighting tube using a professionally treated polycarbonate dome and a prismatic diffuser.

1 Tools & Materials

Essential Tools

  • Plastic Scoring Tool (Crucial for safely cutting brittle acrylic)
  • Angle grinder with metal cut-off wheel (or reciprocating saw)
  • Caulking gun & Cordless drill/driver
  • Fine (220) and medium (120) grit sandpaper
  • Clean rags, rubbing alcohol, tape measure, permanent marker

Materials

  • The Top Dome: Polycarbonate pet fence bubble.
  • The Diffuser: 2x4 ft "Cracked Ice" prismatic ceiling panel.
  • Reflectivity: Roll of polished Aluminum Foil HVAC Tape.
  • Sealants: Marine-grade polyurethane (3M 5200) & closed-cell foam weatherstripping.
  • Hardware & Finish: Stainless self-tapping screws, 6" trim ring, matching elastomeric roof coating.

2 Ground Prep: Optical Treatment & Lens

CRITICAL WARNING: The Melting Point Threat

Verify the pet dome is Polycarbonate (~297°F glass transition). If it is cheap Acrylic/PMMA, it will warp and melt in a standard 210°F optical dye tank. Test a small flange area if unsure.

1. The Optical Soak

  • UV Bath: Submerge the polycarbonate dome to chemically bond UV inhibitors.
  • Tinting: Add a 10% to 20% gray or bronze tint to reduce Solar Heat Gain (SHGC) from the harsh western sun.
  • Hard-Coating: Run through a scratch-resistant hard-coat (SRC) dip to protect against Missouri storm dust and hail.

2. Cut the Diffuser Lens

  • Measure the exact inner diameter of your 6-inch pipe.
  • Trace this circle onto the protective film of your prismatic acrylic panel.
  • Using your plastic scoring tool, firmly trace the circle 15 to 20 times (carve halfway through).
  • Carefully use pliers to snap away excess plastic.
  • Sand edges smooth to prevent spiderweb micro-fractures.

3 Roof Installation (Top Side)

PRO TIP: Protect the Base Seal

Do NOT pull or twist the pipe while cutting it down. Any aggressive movement can fracture the foam core and existing elastomeric base seal underneath.

1. Cut Down the Pipe: Remove the tarp. Use the angle grinder to cleanly cut off excess height, leaving 2 to 3 inches above the roof line. File the edge smooth.

2. Line the Interior: Run vertical strips of aluminum foil tape down the inside of the pipe, overlapping seams by 1/4 inch. Smooth firmly to create a mirror finish as far down as you can reach.

3. Mount the Dome: Wipe the cut pipe flange and bubble mounting ring with rubbing alcohol. Apply a thick bead of marine-grade sealant (3M 5200) to the flat mounting ring and press firmly onto the cut pipe. Drive stainless self-tapping screws through the flange.

🌧️ The Western Weather Ramp (Crucial)

Severe spring storms roll in from the west. Apply sealant over screw heads. Once tacky, paint a thick layer of elastomeric roof coating over the plastic flange, blending down onto the roof. Heavily build up the "uphill" side (facing the dome's peak) so water ramps smoothly over the flange without catching a physical edge.

4 Interior Installation (Bottom Side)

Goal: Create an airtight thermal break to stop the afternoon heat blast and prevent condensation.

  1. Finish the Reflective Lining: From inside the room, finish applying vertical strips of aluminum foil tape up the inside of the pipe until it meets the tape from the roof.
  2. Install the Thermal Break Gasket: Stick the closed-cell foam weatherstripping directly around the inside rim of the pipe, leaving ~1/4 inch space from the bottom edge. This seal must be 100% airtight to stop radiant heat transfer from the western sun.
  3. Mount the Diffuser Lens: Press your "cracked ice" lens up into the pipe so it rests firmly against the weatherstripping gasket.
  4. Secure the Trim Ring: Place your 6-inch recessed trim ring over the lens. Screw the trim ring into the surrounding interior wall or metal collar. The ring acts as a bezel, clamping the lens against the gasket without putting screws through the acrylic.

Ongoing Maintenance

Yearly Check: Inspect the elastomeric coating around the base of the roof flange before the spring rainy season to ensure no cracking has occurred.

Lens Cleaning: Because of the professional optical hard-coat and UV soak, you will not need to regularly sand and recoat the dome. Simply wipe it clean of pollen and dust periodically to maximize light transmittance.