Dear Mr. Marantz,
It has happened again! Part of the kitchen ceiling in our 1929, two-and-a-half story home is disintegrating as water trickled through it last winter. This last happened in 1997 when there was also much snow. On both occasions we had, at the end of a southwest-facing valley, a large ice dam on the edge of our very high and difficult-to-reach roof. The valley is above an interior corner in the outside wall and the two constituent walls descend one story to a small metre-wide roof above the kitchen. In other words the kitchen is wider than the bedroom above. We speculate that water is running down the inside of one or both of these walls and is ending up in the kitchen.
In 1997, in an attempt to fix the problem, the roof was re-shingled and an ice-water membrane placed under the shingles. The roofing company that did the work was called back, but having inspected the roof (from the ground) they were adamant that it could not be melt water, the main argument being that there were no icicles hanging from the 30 cm wide soffit, as opposed to the eavestroughs, where there were numerous daggers waiting to descend! However, the house was re-painted the summer before last and the soffit repaired and caulked, so I would have not expected it to leak. Their suggestion was melting condensation from the attic, but the attic is well sealed and insulated and is also vented on the roof. The vent is clear of snow. Further, why should we get water at just that one spot?
Can you suggest what we should do to cure this problem?
Ice damming and leakage is a common problem in older one and a half and two and a half story homes. Last winter the heavy snow cover that fell in many small accumulations, made the situation as bad as I have seen it in recent memory. In your situation, the roofer may not be entirely wrong about the cause of the leakage, but may also be partially responsible for not looking at the problem from higher up to see if there is damage to the roofing, as well.
The cause of the leakage, from your description, does appear to be from water from the melting ice dam leaking into the kitchen ceiling from the lower roof. No matter what repairs or modifications are done to this roof, it may not completely stop the leakage. The real source of the problem is the ice dam and its cause, which is likely due to poor air sealing and ventilation in the small attics on the upper floor of your home.
You mention that the attic is well insulated, sealed and vented, but which attic are you referring to? In most two and a half stories there are as many as three to six smaller knee-wall or pony-wall attic spaces behind the walls. Often these are improperly converted to closets and have insulation installed between the rafters. This improperly installed insulation can cause heat to be trapped under the roof sheathing, warming the roofing, causing the snow on the roof to melt during the day and freeze at night. These knee-wall areas are normally the true cause of the ice damming as well as poor air sealing in the older homes, in general.
The solution is to investigate the situation on the upper floor more carefully, before we get a heavy snowfall again this winter. The recent light snow may allow for a good opportunity to check the situation above the roof from a ladder and see if ice is already forming. If this is already occurring, you know this is the likely scenario. Once confirmed, you can take a closer look at the short walls in the upper floor and see if there are access hatches for the small attic spaces behind. If not, or if they are being used as closets, modifications or access hatches may be required.
Once the access hatches are installed, or opened, the location and quantity of insulation and air-vapour barrier should be inspected. If the insulation is located between the rafters, on the underside of the sloped roof, it should be removed. The short knee-walls should be insulated and have an air-vapour barrier installed on the warm side. The floor space should also have a thicker layer of insulation and an air-vapour barrier, if possible. The last items that should be present are vents on either the roof or the gable ends, or ideally in both areas. If this is done improperly or poorly, as is often the case in older homes, the ice dams will be a certainty especially with the steeply pitched valley on your home.
Interior repairs, to improve the situation and minimize the ice damming, are not that complex but limited access to the knee-wall attics may make the job difficult, but not impossible, for adventurous homeowners. The roof and gable vents will likely require professional installation, but the insulation removal and repairs may be done personally, from the interior. Upon inspection of the knee-wall areas, if all these are done relatively well, there may be a more complex situation in your home. Consultation and repairs by a building envelope specialist or general contractor, trained in building science, may be required.