Question: We have a 1,300-square-foot bungalow, built in 1970, with a low-slope roof and a vaulted ceiling in the front half. We had a negative energy test before we installed a new high-efficiency furnace and changed to an electric hot water tank in 2012. Our house is rated at 74 per cent on the energy-efficiency scale. At the time of the furnace installation, one of the install techs said we may expect higher levels of humidity because of the condensing furnace and he advised we leave the chimney up for the time being. We have since experienced two winters and have had no problem with humidity, with the level holding around 45 per cent. We will be replacing the shingles this year and would like to have the chimney removed at that time. At present, there are only two people living in the house. What would be your advice on removing the chimney? We enjoy your column in the Free Press and respect your opinion.
Thanks, Cal Carlson
The ideal time to remove an older chimney, which is not in functional use anymore, is when you are re-roofing. This is probably a good idea, but may be more or less difficult depending on the location and type of chimney you currently have. You may have to work a little harder to remove excess moisture from the living space, but that should be possible if you have good exhaust fans in the bathrooms and kitchen.
Because your home was built in the 1970s, you may have either a brick or concrete block masonry chimney or a metal one. Since you have not specified the location or type of chimney, we will explore the issues with removing both types. Starting with the metal type of chimney, which was quite common around that time, these are normally double-walled, B-vent styles and often run up through the middle of the home to terminate near the centre of the roof. These may be quite easy to remove, due to ease of deconstruction relative to masonry chimneys. Since these normally have the lowest portion visible just below the main floor joists in the basement, disassembly can start there. It is quite possible to remove the majority of this type of vent long before the roofers ever arrive.
The key to removing an older metal B-vent is making sure the openings in all the floors and ceilings are closed up after removal. While this is somewhat important in the main floor, it is critical in the ceiling, which also happens to be the floor of the attic. This area must be properly sealed and insulated to prevent warm-air intrusion into the attic. There may be a metal collar that currently serves this purpose, which may be taken out at the same time as the chimney. The corresponding hole in the building envelope could be covered with plywood, drywall, or other sheathing. The next step is to cover the sheathing with a small piece of polyethylene air/vapour barrier, which should be sealed to the surrounding poly with acoustical sealant. Filling in this area with insulation, to match the level in the rest of the attic, is the final chore.
If your home does have a masonry chimney, it may not be necessary to take out the entire structure, depending on location. If the chimney is situated on the outside of the home, removal may be a tricky process. To fully remove the chimney, the exterior siding may have to be patched, along with the roof and eaves. The benefits of taking this down will be minimal and may be no better than insulating and sealing the openings at the top and bottom. That should be easily accomplished with the use of a few cans of blown-in polyurethane foam and a couple of metal caps. Sealing at both the top and bottom will ensure warm air from the home will not leak out through the old chimney. Therefore, the only possible reason to remove this is to prevent further repairs, or if the brick or surrounding wood trim is badly deteriorated. Then, taking this down below the soffits, before sealing the top, may be all that is required.
If the brick or block chimney is located on the inside walls of the home, or runs up through the middle of the building, removal may be the most difficult. It may be necessary to partially remove some walls to access the masonry for dismantling. This will also be a very messy job, as removal is normally done with a sledge hammer or mechanical pneumatic tool. The resulting dust and debris will require isolating the area around the chimney to prevent a major mess inside the home. Fortunately, this step may be avoidable if there is good access to the chimney inside the attic.
A central chimney may be removed above the roof line, without disturbing the rest of the structure. The remaining portions, inside the attic, main floor and basement, may be left intact. The top and bottom will require sealing at any cleanouts and flues, but the major portion of the brick or concrete block may be left in place. This will save a large amount of work and prevent leakage or repairs above the roof in the future. The opening in the roof sheathing will still have to be patched where the old chimney penetrated, but that should be a small job in comparison to removal of the entire unit.
Removing your old chimney when replacing the shingles is a good idea, to prevent needless repairs to a redundant fixture in the future. You may have to take extra measures, such as using exhaust fans more frequently, to prevent higher relative humidity in the home, but that should be easily attainable with a little effort.
Ari Marantz is the owner of Trained Eye Home Inspection Ltd. and president of the Canadian Association of Home & Property Inspectors - Manitoba (www.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 www.trainedeye.ca.