Renovation & Design

ASK THE INSPECTOR: Proper insulation will prevent leakage through skylights

QUESTION: I live in Saskatoon and have a Velux skylight in my son's bedroom that was installed about 16 years ago. It has leaked about three times since its installation, but this winter the leakage from the ice damming has been substantial and has resulted in having to tear out the walls in the bedroom and in the room below.

I am prepared to fund the use of spray-foam insulation around the skylight, but am also questioning whether I should replace the skylight or eliminate it altogether. The skylight opens and is on the northeast side of the house. It was placed in a sloped ceiling of the room about 15 centimetres up from the wall.

There is also a large valley a metre to the left of the skylight where an addition extends perpendicular to the roof and which also has two skylights installed. These do not open and do not as yet appear to have caused leakage, although I can see ice dams have formed below the skylights on that part of the roof, as well. For most of the year, except when covered with snow, these skylights provide a great deal of light to enter the foyer where we have a cathedral ceiling, so I would be very reluctant to eliminate them.

I am concerned about the heat loss from the skylight in the bedroom, particularly, and its contribution to ice damming. Insurance is paying for the work on this, but I cannot afford to have another claim in the future. I would greatly appreciate any advice you could provide.

Thanks, Wanda Wiegers

ANSWER: Leakage from skylights is one of the more common complaints of homeowners, particularly in sloped or vaulted ceilings. While it's often possible to eliminate this issue with proper flashing and insulation techniques, often it can be very difficult to totally prevent some leakage.

Removal and covering up the skylight opening will be an effective way to prevent serious damage in the future, but will not be the only repair needed in your home. You may have what may be called a "perfect storm" of issues that are causing the leakage into your bedroom ceiling and walls.

First, you have a skylight installed in a sloped ceiling, which is almost always problematic. Second, this unit is an operator, which can be opened. The seals, weatherstripping and hardware of these types of skylights often deteriorate over time and can leak simply from age.

Compounding these issues is the location of the skylight near the bottom of the vaulted ceiling, above a valley. This area may be subject to a large amount of rain water and melted-snow runoff, increasing the chance of leakage. The location above a valley may also put the skylight at risk of being covered with blown snow, which can increase the chances of ice damming or leakage through deteriorated seals.

Removing the old skylight, patching the roof sheathing and installing roofing over the old opening may prevent the severe leakage you are seeing, but there's still a good chance you'll have moisture issues with this style of ceiling.

Most older vaulted ceilings were insulated with fibreglass insulation and poor or missing air/vapour barriers. Because there is very limited room for any type of ventilation in this small cavity, and due to the properties of fibreglass batts that easily allow air to pass through, warm-air intrusion from the home is highly likely. This warm air contains moisture that may condense when it hits the cool roof sheathing in the winter, or simply melt the bottom layers of snow above the roof, causing ice dams and premature wear to the roofing. In either case, moisture from melting ice or frost may find its way through the roofing and ceiling coverings into your home.

Having a big hole in the roof filled with a window, which is essentially what your skylight is, will increase the chances of this happening, but may not be the root cause. Your skylights will allow much more heat to escape through the glass and frame of skylight, increasing the chance of ice damming, but may have little to do with condensation within the vaulted ceiling.

Even though the other skylights in the addition are in a vaulted ceiling, I would suspect they have better insulation and air/vapour barriers around them. While there are small ice dams under these fixed units, mainly from escaping heat melting the snow around them, these may be all right to leave in place and may not need major repairs.

However, the bedroom ceiling itself, whether you remove the skylight or try to repair the flashing and roofing around it, will need better insulation and air sealing. This could be done from the interior by removing the ceiling drywall or plaster, which is likely damaged from the water anyway, or from the exterior by removing the roofing and sheathing.

Replacing the existing poor-quality insulation with blown-in high-density polyurethane foam is the key. Filling the entire cavity with this material will provide much higher thermal resistance, preventing melting of snow, while completely sealing the area from warm-air intrusion from the home. The elimination of these two elements, whether the skylight is removed or not, should be enough to prevent a major reoccurrence of the water damage.

In the majority of cases, skylights leak over time, especially in vaulted ceilings. This is not inherent to the design of these roof-mounted windows, but most often due to the installation and air sealing of the area around them. To prevent major damage in the future, this issue must be rectified in your home, whether you decide to remove the older skylight or not.

Ari Marantz is the owner of Trained Eye Home Inspection Ltd. and the President of the Canadian Association of Home & Property Inspectors - Manitoba ( Questions can be emailed to the address below. Ari can be reached at 204-291-5358 or check out his website at



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