Renovation & Design
QUESTION: We live in a condo built in the late 1980s and it has a zero-clearance fireplace. The fireplace is a metal box with the chimney going through the roof around three to four feet. The chimney was starting to rot, and therefore we were unable to use the fireplace as it was not safe. So we decided we would have the fireplace closed and have an electric unit inserted in its place. The condo board was in full agreement with this, as they would like to see all the fireplaces in the building closed for safety reasons.
We hired a fireplace company recommended by the property-management company to close the fireplace. They did this by removing the chimney from the roof, leaving a small stump. The pipe was insulated, supposedly sealed and the electric-log unit inserted. The problem now is that over the past few weeks with all the rain and snow, we have had water drip down into the firebox, causing a sooty mess. One of the main reasons we wanted to have the fireplace closed was because it had dripped rain before, but the fireplace company assured us this would no longer happen.
Now, we have had a quote from a roofing company to remove the remaining part of the chimney that was left and patch and re-shingle the roof. They have said this would stop any future dripping. We would like to know if this is the route we should take and, if so, are there any drawbacks in sealing off the pipe just at the top of the chimney chase?
Thank you for any advice you can give us.
— Betty Ashmore
Answer: Closing off older chimneys when a fireplace or heating appliance is decommissioned can present a couple of potential issues related to moisture intrusion. Only sealing off the top at the roof may be acceptable in some cases, but also closing up the bottom of the chimney or vent may provide the best chance of preventing any leakage at all.
There are a few locations that can be problematic for moisture intrusion or leakage in most fireplaces.
The most common area is the base of the chimney, where it protrudes through the roof. This should be protected from rain or melting snow entering the roof and chimney chase by a good metal flashing. The flashing should be installed in such a way to divert any water away from the chimney, protecting the base from moisture damage, while preventing it leaking under the roofing adjacent to the chimney. Over time, this flashing can become damaged from corrosion or loose at the roof or chimney.
Since the original contractors initially left a small stump above the roofline, I can assume they left the flashing in place, along with a small section of the chase or the actual chimney vent pipe still sticking above the roof. Initially, the roofer you hire should inspect the area to see if they believe the flashing is the culprit for your current situation. If not, the actual chimney chase or pipe may have rusted or rotted through and a driving rain or thick snow on the roof may be responsible for the current leakage. In that case, the entire chimney above the roof and surrounding shingles should be removed and the sheathing inspected for damage. Any damaged sheathing or framing should be replaced with new wood and the top of the old fireplace chase or flue sealed with foam insulation. After sealing, the roof sheathing should be replaced, followed by the proper synthetic roofing felt or waterproof membrane, and finally the roofing itself.
The previous description is likely what the roofers have in mind, but that may not be a complete job. Often, warm air can easily rise up into the old chimney, or the surrounding chase, from the living space below. If there is poor airflow and no heat from the unused fireplace, that moist air can condense when it hits the underside of the new roof sheathing. If this happens during the winter, that moisture can freeze, which will melt once the weather warms in the spring. This can lead to minor leakage, as you have experienced, but also to moisture damage to the roof framing, sheathing or surrounding area.
To prevent this, the top of the old firebox should be insulated and sealed along with the roof repairs. If you insulate and air-seal the top of the chimney/chase and the bottom, there will be little chance that excessive warm or cold air will infiltrate the area. Also, sealing the bottom will prevent excessive heat loss and may slightly reduce your heating bills.
Removing the old chimney to below the roofline and properly waterproofing the roof should be a necessary component of any job involving shutting down an old fireplace. This should prevent the periodic leakage you are experiencing, if it is only related to precipitation, but further work will be needed for other reasons. Air-sealing the bottom of the chimney chase, at the top of the old firebox, should also be completed to prevent excessive heat loss and any condensation and moisture-related issues associated with warm air leaking up into the old cavity.
Ari Marantz is the owner of Trained Eye Home Inspection Ltd. and the past president of the Canadian Association of Home & Property Inspectors — Manitoba (cahpi.mb.ca). Questions can be emailed to the address below. Ari can be reached at 204-291-5358 or check out his website at trainedeye.ca.