Last week I received a call from a client who was concerned about mold that overtime was forming around her attic hatch. Upon closer examination of the hatch, along with the overall attic, I noticed a great deal of frost that had formed on the underside of the roof. This has inspired my 1st blog post.
When warm moisture-laden air in a home seeps into a cold attic, frost will appear in the attic. That's it, it's very simple. When moisture enters the attic during the winter months, it condenses on the underside of the roof in the form of frost. The frost itself doesn’t cause damage, but once it melts, things get wet... This is the time when the damage occurs. Melting frost can cause deterioration of roof sheathing, wet insulation, mold, and water stains on the ceiling. All bad things that you definitely don't want.
Frost Comes From Air Leaks
Frost appears in attics from air leaks or attic bypasses. Of course, any type of exhaust fan needs to be exhausted directly to the outside, not into the attic. Even if the exhaust fan is aligned with the roof vent, this is not good enough. Humid air still likes to find its way back into the attic.
The best way to prevent frost from accumulating in the attic is to seal the attic from all air leaks. Although small air leaks don’t seem to be important, these air leaks can aggravate a lot of frost in the attic. It is important to seal all attic leaks, not just the large ones. Once each small leak is completely sealed, the attic will be frost-free. The only problem with all this kind of air sealing is that the leak is located under the attic insulation, and it is difficult to find all the leaks if the attic insulation is not completely removed. Therefore, it is best to start with something simple.
High Humidity = More Potential Frost in The Attic
The more humid the home, the greater the potential of frost forming in the attic. The homes with the worst frost problems are always the ones with the whole-house humidifiers, which is why I don’t like humidifiers. They destroy houses. If you have frost problems in your attic, be sure to take care of all the easy obvious items before climbing around your attic. And please, turn off your humidifier.
Start by replacing the standard switch on your bathroom exhaust fan with a timer. Run the fan for an hour after using the shower. Once these timers are installed, everyone in the house should be trained to run the bathroom fan for 30-60 minutes after each shower or bath. This is the time required for the indoor humidity to return to normal. Running the fan only during the bath does not bring much benefit.
Some bathroom and shower rooms don’t have properly installed exhaust fans or ones that are inoperable. Please repair or install these as soon as possible. Regardless of what your builder said, or what was installed when you purchased the home, fans are needed in bathrooms.
If you have a kitchen exhaust fan, please use it while cooking. The oven and stove generate a lot of moisture.
Ultimately please consider installing HRV (Heat Recovery Ventilator). HRV replaces humid indoor air with dry outdoor air and collects a lot of heat at the same time. This will greatly reduce the humidity level in the home. If you already have an HRV, make sure it's installed, maintained, and operated correctly.
If you have too many plants (or “weeds”) in your home, get rid of them. I can't say how many is too many, I know as soon as I see it.
If your basement or crawl space is wet and without a vapor barrier, repair it. These are the main factors that cause indoor humidity and attic problems.
House Pressure Affects Frost
The "Stack Effect" is the phenomenon whereby warm air rises in a house and cold air enters to replace it. It is sometimes referred to as the chimney effect because it is also the driving force behind a fireplace draft up a chimney. The higher the house, the greater the chimney effect. Split-level houses with more than one attic space will always encounter the most serious attic problems in the topmost attic.
When a home has a combustion air duct connected to the return plenum (return air duct), the house gets pressurized when the furnace runs, which increases the effects of attic air leaks. Combustion air ducts should not be connected to return plenums; they should just be dropped down into the room.
Unbalanced HVAC piping systems can also cause pressure problems. If there are too many return openings in the basement ductwork, the basement will be under negative pressure while the upper level will be under positive pressure. Sealing all the holes and gaps in the furnace ductwork can actually help reduce the severity of air leaks in the attic. A simple test to determine if your basement is "sucking" is to place the basement door about 1 inch away from being closed and turn on the furnace fan. If the door closes by itself, it is a sign that the ducting is not properly balanced.
Will Adding Attic Insulation Help? Nope!
If the attic doesn’t have enough insulation, it will be warm. Adding insulation will make the attic colder. The lower the attic temperature, the greater the possibility of frost. If you already have frost, adding insulation will make it worse. Start by sealing the air gaps, then add more insulation if required. If your budget only allows one option, just focus on the sealing of the air leaks. This is the most important task at hand.
What About More Roof Vents?
First focus on all the other content listed above. Proper ventilation in the attic may reduce the accumulation of frost, but if not handled properly, simply adding more roof vents may actually cause more frost. But roof vents are a great topic for a future blog.
Author: Barret Beaudry- Sept 2022
Solitaire Home Inspections Ltd.
