Most homeowners refer to skylight parts simply as the “skylight cover.”

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

Over time these plastic components can become yellow, brittle or cracked due to UV exposure, weather and age. When this happens, replacing the skylight cover is usually quick and far more cost-effective than replacing the entire skylight.

This guide explains the different types of skylight covers and how to identify the correct replacement skylight dome or diffuser for your home.

| If your skylight diffuser has turned yellow from age or UV exposure, replacing the diffuser is usually the simplest solution.

A skylight cover is the plastic component that allows daylight to pass through the skylight while protecting the opening from weather and debris.

Most skylight systems use two covers:

• the skylight dome on the roof
• the skylight diffuser on the ceiling

Although people commonly refer to both parts as the skylight cover, each serves a different purpose within the skylight system.

Understanding which part needs replacing will help ensure you order the correct skylight replacement part.

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

Most domes are made from acrylic or polycarbonate plastic 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 your roof skylight domes are 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 often round or square plastic lenses mounted inside 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 the brightness and appearance of the skylight without needing to replace the entire unit.

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

Some of the most common signs that your skylight cover needs replacement include:

• yellow or cloudy plastic that blocks light
• cracks forming in the dome or diffuser
• brittle plastic that breaks easily
• hail impact damage
• water leaks around the skylight

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

Before ordering a replacement skylight cover it is important to determine whether the damaged part is the roof dome or the ceiling diffuser.

You should also confirm:

• the shape of the skylight
• the measurement across the base of the cover
• whether the skylight is round or square

Many homeowners find it easiest to identify their skylight using a measurement guide or visual comparison.

Before ordering a replacement skylight cover, it’s important to measure the outside edge of the existing cover or frame, not the ceiling opening.

Use a tape measure and record the widest point across the cover. For square or rectangular skylights, measure both the width and length. For round skylights, measure the diameter across the centre.

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

If you’re unsure, you can also upload photos and measurements using our skylight part identifier form, and our team will help confirm the correct replacement cover.

Skylight covers are typically measured across the base of the plastic, not the roof opening.

To measure your skylight cover:

Remove the diffuser or inspect the dome from the roof

Measure across the widest part of the plastic base

Record the measurement in millimetres

Common skylight cover sizes include:

• 455mm
• 500mm
• 650mm
• 750mm

Accurate measurement ensures the replacement skylight cover fits correctly.

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

Available parts include:

• replacement skylight domes
• ceiling skylight diffusers
• skylight shafts and trims

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

Browse the full range of replacement skylight parts below.