Skylight Glossary

Definitions of Common Skylight Terms

ACRYLIC SKYLIGHTS – Skylights that are glazed with a plastic lens, most often dome or pyramid shaped.  The lenses can come in clear, white, or bronze and are most often combined with 2 layers to make a double dome. 

CURB MOUNTED – Curbs are typically built with 2×4 or 2×6 wood studs secured to the roof deck and made water tight with paper, underlayment, and flashing.  Skylights mount on top of the curb and sit over top of it like the lid on a shoebox.  It is secured with screws.

DECK MOUNTED – Deck mounted skylights are mounted directly to the roof deck and have lower profile than curb mounted, but are more difficult and costly to replace.

DIFFUSED LIGHT – Indirect light.  Skylights can diffuse light with white acrylic domes, or white frosted glass, or can even use light filtering blinds.

FIXED SKYLIGHT – A fixed skylight is secured down to the roof and does not open or vent.

FLASHING – A waterproofing system, usually made up of thin sheet metal, that seals the skylight to the roof deck.  Header flashing, pan flashing, step flashing are all different types of flashing.

FRAME – The metal framing that encases the glass of the skylight.  Skylight frames are typically made of aluminum.

GLAZING – The glass portion of the skylight.  It can come in all different thicknesses and purposes, like filtering out harmful UV and laminated safety glass to ensure no glass will fall from above.

JOIST – Ceiling joists are the parallel stud beams that support your ceiling.

LAMINATED GLASS – 2 panes of heat-treated glass bonded together with vinyl that creates a bond if ever broken.  Laminated Glass is required in all skylights in California.

LoE3 – A metallic coating that helps improve glass energy efficiency as well as block harmful UV and fading rays. Velux Skylights use LoE3 on all of their glass skylights.

PITCH – The pitch of a roof is its angle or slope. 

RAFTER – Roof rafters are the parallel stud beams that support a sloped roof.

ROOF DECK – The supporting skeletal structure that sits on top of the roof rafters, typically made of wood.  The roof deck is what your roofing material (shingles) attach to.

ROOFING MATERIAL – A waterproof covering often times consisting of individual overlapping elements.  Common roof types include, shingles, shake, composite, tile, and modified bitumen touchdown. 

ROUGH OPENING – The dimensions referred to the actual size of the cut out of the hole into the roof deck.

SELF-FLASHING – Self-flashing skylights have built-in metal curbs and can be installed directly to the roof deck without having to build a traditional curb. The downside to self-flashing skylights is that they typically require roofing work and resealing when replacing, which drives up the installation cost.

SHADES – Pleated shades, exterior shades, or interior blinds that range from light filtering to room darkening, all the way to blackout. 

TEMPERED GLASS – Glass that has been heat treated and hardened to the point that when it shatters, it breaks into lots of small pieces, rather than dangerous shards.  The tempered layer is the outer shell of the glazing system on a skylight.

TRUSS – Rigid frameworks designed to support the load of a structure.

UNDERLAYMENT – A sticky layer of special waterproofing material put down to bond the skylight with the flashing.

UV LIGHT – Ultraviolet light that can fade and damage the interior of your home.  Velux uses LoE3 glazing on all their glass skylights that block 99% of UV light.

VENTING SKYLIGHT – A skylight that is hinged on one side and the top opens up to provide fresh air to the inside.  They can be manually operated or solar powered.