403-875-0770 scott@mastersgroup.ca

This week’s discussion comes from a problem one of our customers had in her home. Jill, who owns a house in Glenbow, contacted us to come and have a look at a wet spot in her drywall ceiling. Located beside her bed it started to drip on to her carpet and was keeping her up at night. After some investigation, we discovered she had developed a large accumulation of frost under her roof sheathing which started melting with warmer weather, creating the leak.

Now, before we discuss how we helped Jill, let’s go over the two most common calls we get for water leaks into a house during our winter freeze/thaw season.

Ice damming:

An ice dam is a ridge of ice that forms at the edge of a roof and prevents melting snow from draining off the roof. The water that backs up behind the dam can leak into a home and cause damage to walls, ceilings, insulation, and other areas. There is a complex interaction among the amount of heat loss from a house, snow cover, and outside temperatures that leads to ice dam formation. For ice dams to form there must be snow on the roof, and, at the same time, higher portions of the roof’s outside surface must be at a warmer temperature than the lower surfaces near the gutter line. The snow on a roof surface that is warm, due to the sun or attic heat loss, will melt. As water flows down the roof it reaches the portion of the roof that is colder and freezes. Voila! –You built an ice dam.

The dam grows as it is fed by the melting snow above, but it will limit itself to the portions of the roof that are, on the average, colder than the rest of the roof. Therefore, the water above backs up behind the ice dam and remains a liquid. This water finds cracks and openings in the exterior roof covering and flows into the attic space. From the attic it could flow into exterior walls or through the ceiling insulation and stain the ceiling finish.

Attic rain:

Attic rain occurs when warm moisture accumulates in the attic, freezes during cold temperatures, then melts when the weather warms again. The buildup of frost under the sheathing melts, makes its way through the attic insulation and then into your drywall ceiling. This seesaw in weather produces the perfect “attic-crying” conditions to damage your house. The kicker? It usually affects newer homes more because there are less places for air to escape.

The solution:

There are many things a home owner can do to help reduce attic rain and ice damming:

  1. Check to see if your attic is well ventilated as insufficient roof or soffit vents will limit the amount of air exchange in your attic.
  2. Have a contractor assess the R-value of your insulation. This can lead to more than normal heat loss into your attic, creating condensation under the roof sheathing.
  3. Make sure your exhaust fans are vented directly outside, as many times the duct work from a bathroom fan will come loose from the roof sheathing and you will be blowing warm, moist air into your attic.
  4. Turn down your humidifier; the ideal moisture level for your house is 30%-50%.
  5. Turn on your kitchen exhaust fan during cooking and remember to run your bathroom exhaust fan during a shower or bath.
  6. Check the area around your attic hatch; there should be insulation on top of the hatch itself along with a good quality foam weather strip on the ledge where the hatch rests. You would be surprised to see how many homes have excessive frost build up under the roof sheathing just from this problem alone.
  7. For ice damming, make sure your gutters and down pipes are cleaned at the end of the summer season. This will help direct any excessive snow melt away from your eave line quicker, reducing the amount of ice buildup on the edge of your roof. If the problem persists you may have to contact a qualified roofing professional to assess the condition of the shingles and the underlayment.


So, back to Jill; what was causing her attic rain/frost buildup? We had determined that the bathroom exhaust fan duct that normally would have been connected through the roof had come loose and was laying in the insulation above her bedroom ceiling. Every time Jill turned on the fan it blew warm moist air into the attic and would then rise and freeze to the underside of the roof sheathing. As soon as the temperatures warmed, that frost melted and the attic rain would start, dripping into her insulation and finding its way through to her ceiling. Within a couple of hours we had the duct work fastened properly to the roof vent and the problem solved.

As always, check with the experts and professionals that will take time to find and fix the problem.