Most homeowners refer to skylight parts as a “skylight cover.”

In most residential skylights, this “cover” is actually one of two components:
the roof dome on the roof, or the ceiling diffuser inside the ceiling.

These plastic components can become yellow, brittle or cracked over time due to UV exposure and weather. Replacing the damaged part is usually faster and more cost-effective than replacing the entire skylight.

This guide helps you identify the correct replacement dome or diffuser using part type, shape and measurements.

Because these parts are different, they are also measured differently — always confirm which part you are replacing before ordering.

Skylight “covers” can refer to a roof dome or ceiling diffuser, and they are measured differently. Choose your part type first, then follow the correct measuring guide below.

A skylight cover is the plastic component that allows daylight into your home while protecting the skylight opening from weather and debris.

Most skylight systems use two covers:
the roof dome on the roof, and the ceiling diffuser inside the ceiling.

These parts work together but are separate components, and each may need to be replaced at different times.

The skylight dome sits on the exterior of the roof and allows light into the skylight shaft while protecting the opening from rain, wind and debris.

Most domes are made from acrylic or polycarbonate and are exposed to harsh outdoor conditions. Over time, they can deteriorate due to:
• UV exposure
• hail damage
• falling branches
• general ageing of the plastic

If a dome becomes cracked or damaged, it should be replaced promptly to prevent water entering the skylight shaft.

The skylight diffuser is the ceiling component that spreads daylight evenly into the room below.

Diffusers are typically round or square plastic lenses fitted within the ceiling frame.

They are commonly replaced when they become:
• yellow or discoloured
• brittle with age
• cracked from impact
• loose within the ceiling frame

Replacing a skylight diffuser restores brightness and appearance without needing to replace the entire skylight.

Skylight covers naturally deteriorate over time due to sunlight and weather exposure.

Common signs your skylight cover needs replacement include:
• yellow or cloudy plastic reducing light
• cracks in the dome or diffuser
• brittle plastic that breaks easily
• hail or impact damage
• water leaks around the skylight

Replacing a damaged skylight cover early can help prevent further damage to the skylight shaft and surrounding roof area.

Before ordering a replacement, first determine whether the damaged part is the roof dome or the ceiling diffuser.

You should also confirm:
• the shape of the skylight (round, square or rectangular)
• the part type you are replacing (dome or diffuser)
• the relevant measurement for that part using the correct guide

Skylight domes and diffusers are measured differently, so always follow the matching measuring guide or compare your skylight visually before ordering.

Some homeowners find it easiest to identify their skylight using our video guides.

Before ordering a replacement skylight cover, first confirm whether you are measuring a roof dome or a ceiling diffuser, as these parts are measured differently.

Roof dome: measure across the plastic dome base, edge to edge at the widest point.
For square or rectangular domes, measure both width and length. For round domes, measure the diameter across the centre.

Ceiling diffuser: measure the ceiling opening or compare the diffuser size and frame style with the product listing.

Measurements do not need to be exact to the millimetre, but getting close will help match the correct replacement size.

If unsure, upload photos and measurements using our skylight part identifier form and we’ll confirm the correct replacement before ordering.

Skylight covers are not all measured the same way. The correct measurement depends on whether you are replacing a roof dome or a ceiling diffuser.

To measure correctly:
• confirm whether you have a dome or diffuser
• follow the matching measuring guide for that part
• use your measurements to match the closest available size

Common skylight sizes include:
• 455mm
• 500mm
• 650mm
• 750mm

Accurate measurement and part identification ensures your replacement skylight cover fits correctly.

Skybrite supplies skylight replacement parts for many common residential skylight systems.

Available parts include:
• replacement skylight domes
• ceiling skylight diffusers
• skylight shafts and trims

Skylight parts are identified by size and shape, not brand, making it easier to match the correct replacement even when the original system is unknown.

All parts are shipped from Brisbane with delivery available across Australia and New Zealand.