Step 6: Flashing the Window

ATTENTION! All products manufactured by Sun Windows must be properly flashed and a complete vapor barrier applied to seal the product opening. Proper installation of drainage systems, flashing, water and vapor barriers are the sole responsibility of the owner or their agents.

a) Apply side flashing tape. Cut 2 pieces of flashing tape 4” to 6" longer than the rough opening height. Apply one piece to each side, covering the nailing fin and sealing against the weather resistive barrier or sheathing. The tape should extend 2” to 3" below the bottom of the opening and 2” to 3" above the top of the opening.

If your window is a single unit (one unit wide) skip to step 6 c)

Note: On multi-wide units a separate drip cap must be installed. This drip cap must run the entire width of the multi unit. It must form a drip edge that extends beyond the top, outer most face of the window unit. It must form a 90° angle at the back and cover the nailing fin. This cap may be purchased pre-formed from a building materials supplier or it may be made from typical aluminum flashing, available in rolls (coil stock) from a building materials supplier.

b) Install the drip cap on top of the window and fasten it to the wall sheathing with galvanized roofing nails.


c) Apply top flashing tape. Cut 1 piece of flashing tape long enough to go across the top of the window and extend at least 1” past each piece of side flashing tape. Apply the tape so that it covers the nail fin and seals against the exposed sheathing (left exposed in step 2 c).

d) Fold top flap down. If a weather resistive barrier was used, fold the top flap (temporarily taped out of the way in Step 2 c) down over the top flashing tape applied in the previous step.

e) Apply corner flashing tape. On weather resistive barrier applications, cut 2 pieces of flashing tape at least 1” longer than the diagonal cuts on the top weather resistive barrier flap. Apply the tape to each top corner so that it completely covers each diagonal cut and overlaps the top corners.

ATTENTION! Do not apply flashing tape to the bottom nailing fin.

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Step 7: Insulating & Applying Interior Seal

a) Apply fiberglass insulation. Loosely fill the space between the window and the rough opening with fiberglass insulation. Be careful not to pack the insulation too tightly. Over packing may cause the window to bow.









b) Apply backer rod. Apply 1/4” backer rod over the fiberglass insulation and press in place so that it is recessed approximately 3/8” to 1/2”.




c) Apply sealant. Apply High Grade Exterior Sealant over the backer rod and tool to finish the seal.




d) Alternate Method: Apply foam insulation. Using a quality low expansion foam, apply a 2” thick bead of foam approximately 1” deep into the space between the window perimeter and the rough opening framing. Note: no backer rod or caulk seal is needed for this method.

ATTENTION! Do not use high expanding foam as it will cause the window to bow. Follow foam manufacturer’s recommendations for application.

e) Apply interior trim. After insulating and sealing the window perimeter apply interior trim. With the exception of radius casing (trim), all trim is supplied by sources other than Sun Windows. Follow traditional methods for applying trim. Do not used excessively long trim nails. Trim nails should penetrate 3/8" to 1/2". Exceeding 1/2" may damage operating components of the window. Sun Windows Interior Casing for radius window products may require manipulation to conform to the curve of the window product. Begin by fastening at the center point of the window curve and work to the outer edges, fastening as proper alignment is achieved.

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