Curb Mounted Skylights

Model MCM  Skylights 

Mac Curb-Mounted Skylights are out most commonly used skylight model as they can be installed onto virtually any type of roof. They incorporate a thermally broken aluminum base frame, which is an important feature in colder climates. This thermal break consists of a core of structural, insulative material, which divides the warm inner portion and the cold outer portion of the aluminum frame, thereby increasing thermal efficiency. Glazing consists of single, double or triple layers of thermally formed acrylic domes. The elevated profile of the domed shape helps to shed snow during winter months. This is an important consideration for our long Canadian winters, as the skylight must remain free of snow to provide maximum illumination. During winter months the number of hours of daylight are at the lowest, and people generally spend more time indoors.

Mac Curb-Mounted Skylights are designed to fit onto a curb constructed on top of the roof. The construction of these curbs may be modified to suit various roof types. Typically the curb consists of wood or metal structure, rigid insulation, roof membrane and/or flashings, a vapor barrier, and interior finishing material.

Standard Curb Construction, as outlined on the details page, is typical on most sloped roof installations, or when the thickness of the required roofing materials is minimal. The curb construction method allows for a wood curb, 1-1/2” (38mm) thick, insulated with 1” (25mm) of rigid insulation, and waterproofed with membrane roofing and/or flashing. The total curb thickness must not exceed 2-3/4” (70mm). The height of the curb may be adjusted to suit specific jobsite conditions. If this construction method is being utilized, then the rough opening dimensions shown on the size chart in the standard sizes page are applicable. Many of these sizes are intended to line up to standard rafter and truss spaces.

If for any reason the thickness of the roof curb will exceed 2-3/4” (70mm) then Wide Curb Construction will apply. Many different curb construction methods may be utilized. One typical wide curb detail is illustrated in the details page. This common on flat roof installation due to the added thickness of most roofing systems, or with additional insulation with in the curb is desired. The same skylight is used with either Standard Curb or Wide Curb Applications. The outside dimensions of the skylight remains as per the standard sizes indicated in the Standard Sizes Page. The rough opening of the skylight is reduced to accommodate the added thickness of the curb materials. The rough opening must be calculated by subtracting two times the actual curb thickness from the outside dimensions.

The Mac Model MCM Curb-Mounted Skylight is the most versatile skylight available, not only because of it’s adaptability to various roof types, but also because of the many options offered. This includes a wide variety of sizes, shapes and glazing and operability options as outlined on this and some of the following pages. Although not illustrated, Mac Model MCM Curb-Mounted Skylights may also be custom fabricated with special flashings to permit installation directly against adjacent vertical walls. This can be particularly effective when installed on the edge of a buildings’ foundation to allow natural illumination of basement areas.

The drawing in the details page illustrates the same Mac Model MCM Curb-Mounted Skylight installed onto two different types of roof curb. Note that the outside dimensions remain consistent and that it is the rough opening that is reduced to accommodate increased curb with. The chart in the specifications page indicates standard sizes available. The rough opening dimensions listed are for Standard Curb Construction. The rough opening dimensions for Wide Curb Construction must be calculated by subtracting the thickness of the required curb, multiplied by two, from the outside dimension of the skylight. Remember to allow some exterior clearance for expansion and contraction, and for the buildup of the roofing material at lapped Corners.