installing flat rectangular skylights

Flat skylights installation is a relatively complex task, with particulars dependent on the roof type and skylight models. Hire a professional to get a proper installation, unless you are a skilled person engaged in a DIY solution.

Below we list the main steps associated with a basic installation of a flat self-flashed skylight. They are especially valid to the basic model of the largest world skylight manufacturer (Velux).

Those installation steps are valid for roofs with a pitch between 15-60° and asphalt shingles up to 5/16’’/8mm, and are a rather schematic approximation to a relatively complex process.

Installation steps for rectangular self-flashed skylights

1Flat Skylight Installation 1
The first step involves the cutting and framing of the skylight opening, which should have into account the skylight dimensions and the measurements indicated by the manufacturer.

As shown in the image, asphalt shingles are installed to bottom of the opening. Framing headers should be placed perpendicularly to skylight; you also should install a proper underlayment on the roof deck.

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Flat Skylihght Installation 2To align the skylight in the opening, install position blocks, and then tack the skylight with roofing nails. See image.

3Flat Skylihgt Installation 4
Each skylight bracket should be fixed to the roof with the nails provided by the manufacturer. Nails should penetrate the roof rafter or truss (typically through angled holes). 

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Flat Skylight Installation 3 Install the shingles tightly against the sides of the skylight. Nail the shingles to the flexible flashing flange, to tightly secure the shingles. See image.

5Flat Skylight Installation 5
Notch the asphalt shingles around the head flashing, closely, without leaving gaps.

6Flat Skylight Installation 6
The head flashing should be overlapped with underlayment (to ensure proper drainage). Self-sealing rubberized asphalt-sheet and roofing paper about 8 inches wide are largely used on underlayment. Underlayment and flashing should be installed correctly to avoid leaks around the skylight. See image.

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The final steps of the skylight installation involve installing and notching asphalt shingles close to the head flashing. The metal parts of the flashing should not be nailed. Before installing drywall or other tunnel finishing material, the installer should remove the positioning blocks used to ensure the skylight alignment.

Images credit: Velux America

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