Plenty of houses built or renovated between the 1970s and 1990s still have their original plastic bubble skylights: a clear or smoky acrylic dome sitting on a wooden box on the roof. Many of them are now yellow, hazy, brittle or dripping condensation every cold morning. Skylight dome replacement is one of the most common requests we get for these units, and the good news is that there are more options now than simply ordering another bubble.
This article explains how old domes fail, what we check on the curb underneath, how a new dome compares with a curb-mounted glass skylight, when resizing the opening makes sense and what changes on the ceiling side once the work is done.
Why Skylight Dome Replacement Comes Up So Often
Skylight dome replacement is usually triggered by one of three things: the dome looks bad, the room below is uncomfortable, or water is getting in. Behind all three is the same fact. Acrylic domes of that era were a simple, affordable product, but the material degrades under decades of ultraviolet light and temperature swings, and many were single layer with almost no insulating value.
Here is what we typically find on older bubble skylights:
- Yellowing and haze. Ultraviolet exposure breaks down the surface of the plastic. The light that comes through turns dull and yellow, and the dome no longer looks clear from inside.
- Crazing. A network of fine surface cracks spreads across the dome. Crazing weakens the plastic and gives water a foothold.
- Brittleness and cracks. Old acrylic can crack from hail, a dropped branch or even someone stepping on it during roof work. A brittle dome can fail suddenly.
- Heat loss and condensation. A single layer of plastic loses heat quickly. Warm indoor air hits the cold dome, and droplets or frost form and run down into the shaft.
- Tired seals and fasteners. The gasket or sealant between dome and curb dries out, and the screws or clamping frame loosen or rust.
Any one of these can justify skylight dome replacement. When several show up together, which is usual on units of that age, the case is clear. For a full picture of how we handle these jobs, see our skylight replacement service for older and failing units.
| Symptom | What is happening | What it means for the job |
|---|---|---|
| Yellow or cloudy dome | UV damage to acrylic surface | Cosmetic and light loss; dome replacement needed, curb may be fine |
| Fine web of surface cracks | Crazing from age and thermal cycling | Plastic is weakening; plan replacement before it cracks through |
| Frost or droplets on cold mornings | Single layer dome and uninsulated shaft | Choose a multi-layer or glass unit and insulate the shaft |
| Water staining after rain | Failed seal, cracked dome or curb flashing | Inspect curb and flashing before choosing a product |
| Soft or dark wood at curb | Long-term water or condensation damage | Curb repair or rebuild added to the scope |
Start With The Curb, Not The Dome
The dome is what you see, but the curb decides how the job goes. On most bubble skylights of that era the curb is site-built: a box of dimensional lumber nailed to the roof deck, with the roofing carried up its sides and sometimes a metal cap on top. Over thirty or forty years, that box has absorbed whatever water got past the seal and whatever condensation ran down the inside.
On inspection we look at four things:
- Soundness of the wood. We probe the top and sides. Soft, crumbly or dark wood means rot, and a new skylight should not be fastened into it.
- Height. Many old curbs are short. A curb that barely clears the roof surface leaves the skylight vulnerable to ponding water on a flat roof and to snow buildup in winter. Manufacturers state a minimum curb height for their products, and the roofing membrane manufacturer usually has its own requirements for how high the membrane is carried up.
- Square and level. A curb that has twisted or settled will not seat a new unit evenly, which breaks the seal.
- How it ties into the roofing. On a flat roof, the membrane at the curb is often the oldest, most patched part of the roof. Its condition decides whether the curb can be reflashed cleanly or needs roofing repair around it.
If the curb is sound, skylight dome replacement can be quick. If it is rotted or too low, the curb is rebuilt first, and the project becomes part roofing job, part skylight job. It is far better to know this before choosing the new product, because the curb dimensions determine what will fit.
Your Replacement Options
There are three realistic paths for skylight dome replacement, and one alternative worth considering in some rooms.
Option 1: A new acrylic or polycarbonate dome
The most direct route is a new dome made to fit the existing curb. Current domes are commonly available in double-wall or triple-wall versions, which trap air between layers and perform much better than an old single layer. Polycarbonate is tougher against impact than acrylic, while acrylic generally holds its clarity well. A new dome keeps the familiar look and is usually the lowest-cost option. The trade-off is that even a multi-wall plastic dome does not insulate as well as modern insulated glass, and plastic can scratch and age again over time.
Option 2: A curb-mounted glass skylight
For many homeowners, this is the upgrade that makes the job worthwhile. A curb-mounted glass skylight replaces the bubble with a flat or slightly sloped unit of insulated glass, typically with a low-emissivity coating, gas fill and a laminated inner pane. It sits on the curb like the dome did, but with far better heat performance, clearer light and a quieter sound in heavy rain. Glass units come in set sizes, so the curb dimensions matter; the existing curb may fit a standard size, or it may need adjusting. Our flat roof skylights range covers these curb-mounted models.
Option 3: A venting glass unit
If the dome sits over a bathroom, kitchen or stairwell that holds heat, this is a good moment to switch from a fixed dome to a venting skylight. Solar-powered venting models avoid running new wiring through a finished ceiling. See the solar-powered fresh air skylight for how that works.
An alternative: a tubular skylight
If the existing dome sits over a small space and the shaft has persistent condensation problems, some homeowners choose to close the old opening and install a tubular skylight instead. This is a bigger change and involves patching the roof and ceiling, so it is usually considered only when the original opening was a poor fit for the room.
| Option | Heat performance | Light quality | Typical cost range (estimate) |
|---|---|---|---|
| New multi-wall plastic dome | Better than old single-layer, below insulated glass | Clear to diffused, depending on tint | Often around $800 to $2,000 installed on a sound curb |
| Curb-mounted fixed glass skylight | Good, with low-E coated insulated glass | Clear, full view of sky | Often around $1,800 to $4,000 installed |
| Curb-mounted venting glass skylight | Good, plus ventilation | Clear, full view of sky | Often around $2,500 to $5,000 or more installed |
| Curb rebuild added to any option | Improves if insulated | No change | Often adds several hundred to about $1,500 |
All figures are broad estimates that vary with unit size, roof type, access, roofing repairs and interior finishing. A site visit is the only reliable way to price a specific skylight dome replacement.
Keeping The Size Or Changing It
Most skylight dome replacement work keeps the existing opening. That is the least disruptive approach because the roof framing, curb and interior shaft all stay where they are. If the old dome was an odd size, which is common with older units, the curb can often be adjusted with added framing so it matches a standard modern unit.
Resizing is worth considering when the original skylight was clearly too small or too large for the room, or when you want to switch products and the opening does not suit any standard size. Enlarging an opening means cutting roof framing and adding headers, and it may require a building permit depending on the municipality and the extent of the structural work. Shrinking an opening means infilling the roof deck, adjusting the curb and reworking the shaft and ceiling opening inside. Either way, it is a bigger job than a same-size swap and deserves careful pricing.
| Approach | Roof framing | Curb work | Interior impact |
|---|---|---|---|
| Same size, new dome | No change | Repair or reseal only | Minimal, usually shaft paint touch-up |
| Same opening, standard glass unit | No change | Framing added or trimmed to match unit size | Minor drywall and paint at the top of the shaft |
| Enlarged opening | Rafters cut and headed off; permit may apply | New curb built | Shaft and ceiling opening rebuilt larger |
| Reduced opening | Roof deck infilled | New smaller curb built | Shaft reframed, ceiling patched and refinished |
| Closed and replaced with a tube | Old opening infilled; small new hole cut | Old curb removed | Old shaft closed, ceiling patched, diffuser fitted |
Before you decide to resize, look at how the light behaves in the room today. A small dome over a long hallway may be better served by adding a second unit or flaring the shaft than by cutting a bigger hole. We work through these decisions with homeowners across the GTA, including our Halton Region skylight installation, replacement and repair team, and the answer always depends on the room, not the address.
How The Work Is Sequenced On The Roof
A typical skylight dome replacement on a flat roof follows this order:
- Protect the interior. Floors and furnishings below the opening are covered, since debris can fall into the shaft.
- Remove the old dome. Fasteners or the clamping frame are removed and the dome is lifted off. Old acrylic is often brittle, so it is handled carefully to avoid shards.
- Inspect the curb top and inside faces. With the dome off, rot and gaps are easy to see.
- Repair, raise or rebuild the curb as needed. Rotted lumber is replaced, height added if required, and the curb squared to fit the new unit.
- Reflash the curb. The roofing membrane or flashing is carried up the curb sides in a way that is compatible with the existing roof system. This step matters most for long-term watertightness.
- Insulate the curb. Where possible, rigid insulation or insulated framing reduces the cold spot at the curb that drives condensation.
- Set and fasten the new unit. The new dome or glass skylight is placed on the curb, fastened per the manufacturer’s instructions and sealed.
Early autumn is a good time for this work. Temperatures are usually suitable for roofing membranes and sealants, and a new unit goes into the colder months already sealed and insulated, which is exactly when an old dome would drip the most.
What Changes Inside The Room
Homeowners are sometimes surprised by what a skylight dome replacement changes on the ceiling side. The main differences:
- Brighter, whiter light. Removing a yellowed dome restores clear daylight. With glass, the view of the sky is sharp rather than blurred.
- Less condensation. A multi-layer dome or insulated glass keeps the inner surface warmer, so less moisture forms. An insulated curb and shaft help further.
- Shaft touch-ups. Old water stains, peeling paint and cracked drywall at the top of the shaft usually need repair. If the shaft was never insulated, this is the moment to do it.
- A quieter room. Glass units and multi-wall domes generally transmit less rain noise than a thin single dome.
- Option for shading. Many glass skylights accept factory shades. If the room overheats in bright sun, a light-filtering skylight shade softens it without darkening the space.
Questions To Settle Before You Book
A little preparation makes the quote easier to compare:
- What are the outside dimensions of the curb, and does a standard unit fit?
- Is the curb sound, and if not, is the rebuild priced separately?
- How will the new flashing tie into the existing roofing membrane?
- What glass package or dome wall construction is proposed?
- Will the curb and shaft be insulated as part of the work?
- Who handles the interior drywall and paint repair?
- Is the unit fixed or venting, and is that the right choice for this room?
If the roof itself is close to replacement, ask about timing. Doing the skylight dome replacement at the same time as the roofing avoids flashing the new unit into old membrane that will be torn off in a year or two.
Dome Skylight Questions
Can I replace just the plastic dome on my skylight?
Why does my bubble skylight drip in cold weather?
Is glass better than a new acrylic dome?
Will a new skylight fit my old curb?
How long does skylight dome replacement take?
Should I make the opening bigger while I am at it?
Plan Your Skylight Dome Replacement
If your bubble skylight has turned yellow, crazed or started dripping, a combined look at the dome, curb and roofing will show which option makes sense. Toronto Skylight Installers will check the curb, measure for standard units and explain the choice between a new dome and a glass skylight in plain terms.
Call us today at (416) 365-7557 or request a free estimate.
Serving homeowners in Halton Region and across the wider GTA with skylight installation, replacement and repair.