Based on the size of your VELUX Roof Window or Skylight, determine the best location to open your ceiling from inside the room. The ceiling opening should be larger than the roof opening to provide better light distribution and easy removal of insect screen on ventilating units.
From the crawl space, remove all ceiling insulation, electrical wires, etc. from above the ceiling opening. Using the ceiling joist as a guide, locate the two bottom corners of your ceiling opening and plumb up to the roof deck to locate the bottom of the roof rough opening. Now mark the rough opening using the dimensions on the previous page. Drive nails up through the roof deck at all four corners of your measured opening. Nails should go through to the outside of the roof. From the roof, remove shingles from around the rough opening to expose roof deck. Save old shingles for reuse when flashing. Snap hackled line on the roof deck between corner nails to mark the rough opening. Make sure the rough opening is level and square. Cut and remove the roof deck at chalk lines.
2. CUTTING THE ROOF RAFTERS (if necessary)*
If rafters are cut, each one must be supported and braced from underside of roof. Supports must be left in place until headers are installed. Mark cutting lines on rafters as indicated below. Center rafter(s) should be cut at an angle so the headers will run flush with the flared soffits. Cut and remove the center rafter(s).
* Roof trusses should not be cut without consulting local building codes, local ordinances, and engineering requirements. If there is a problem cutting trusses, choose a size that will fit between trusses.
3. FRAMING THE ROUGH OPENING
Remember, the rough opening is determined by the size of the VELUX Skylight. See precise rough openings on the dimensions chart. Install headers at the head and sill between the rafters. If you've had to cut a rafter, we suggest doubling the headers (See Framing Options). Framing on the roof is now complete.
4. INSTALL AND FLASH SKYLIGHT
Complete preparation/installation and flashing of the skylight (refer to appropriate sections).
5. PREPARE AND CUT CEILING OPENING
Drop a plumb line from each corner of the skylight to determine the minimum ceiling opening. Expand/flare this opening to provide better light distribution and air movement to help reduce any chance of condensation. To flare the opening, draw new lines for the top of the ceiling opening to expand the light shaft as shown. Following the procedures used to cut rafters(Step 2) and frame roof opening, cut and frame ceiling joist (if necessary), as shown. The ceiling joist must be supported before cutting.
6. BUILD AND FINISH LIGHT SHAFT
Frame the light shaft wall with studs at 16” or 24” on center, and nail to existing ceiling joist. Finish the inside of the shaft with dry wall or other finish material. Insulate around the light shaft and skylight to prevent heat loss, air infiltration and condensation. Use either rigid or batt insulation.
