Frequently Asked Questions
- How important is a bathroom exhaust fan that vents properly through my roof?
- How do I protect my home against ice dams?
- How long should a roof last?
- What is the difference between the contractors warranty and the manufacturers warranty?
Bathroom and kitchen fans are an important part of your home's ventilation system. They remove odours from your house, which improves indoor air quality. Fans also remove moisture, which decreases the level of humidity in your house. High humidity can damage building materials and can cause mold growth which in turn may affect your family's health.
Too often, we see newly renovated bathrooms with the vent exhausting directly into the attic space or incorrectly connected or vented through the roof.
How good is the fan I have now?
CMHC's research shows that many houses have exhaust fans that:
- are too noisy
- move very little air
- are not energy efficient
- may cause back drafting of combustion appliances
- use high-wattage lighting
- are vented directly into the attic
- are vented into the soffit area or not properly vented through the roof
To find out if your exhaust fan is drawing air, hold a piece of toilet tissue up to the grill. The exhaust air should hold the tissue tightly to the grill. You could also check the outlet to make sure the air is leaving your house.
Seal and then insulate all ductwork running through unheated areas to avoid moisture problems. Slant horizontal runs of duct down toward the exterior outlet to drain any condensation outside. Seal it tight to a proper bathroom exhaust vent with a flapper.
Exhaust air should not be released into the attic, into a wall or ceiling cavity, crawl space, basement or in the roof soffit. These locations can promote condensation damage and mold growth.
Fans create static electricity, which attracts dirt like a magnet to the fan and its housing. The dirt can encourage mold growth and restrict air movement. Clean fans, housings, backdraft dampers and exterior flaps seasonally. A typical bathroom fan can be cleaned by pulling down the grill, and unplugging and removing the fan module. Fans in ducts and exterior fans may be difficult to clean, however.
- Install exhaust systems according to the building code and manufacturer's recommendations. Straight, short duct runs, with few turns, will result in the highest fan flow.
- For bathroom fans, use duct with a diameter of at least 100 mm (4 in). For long runs, use larger, 150 mm diameter (6 in.) to improve air flow. It is usually best to avoid fans with 75 mm (3 in.) exhaust ports and ducts. Follow manufacturer's instructions for kitchen exhaust duct sizes.
- Seal all duct joints and connections with aluminum duct tape or duct mastic (available at contractors. supply shops) to prevent air, moisture and noise leakage. Standard cloth duct tapes tend to dry out and fall off.
- Seal and then insulate all ductwork running through unheated areas to avoid moisture problems. The best practice is to slant horizontal runs of duct down toward the exterior outlet to drain any condensation outside.
- Exhaust air should not be released into the attic, into a wall or ceiling cavity, crawl space, basement or in the roof soffit. These locations can promote condensation damage and mold growth.
Chimney Connections Warning!
Some older bathrooms have static exhausts which look like upside down funnels on the ceiling. If these exhausts are hooked into the furnace chimney, disconnect them from the chimney, seal the hole in the chimney with hydraulic (expanding) cement, and install a new powered exhaust. If these static exhausts go directly outside, they can still be used, but a good fan will be more energy efficient and less drafty.
Ice dams are formed when heat from the inside of a home escapes into the attic and warms the roof decking during the winter. This heat, combined with heat from the sun, can melt snow on the roof. Melting snow then runs down toward the eaves as water. When it reaches the cold eaves and gutters, it refreezes. This continual thawing and re-freezing process creates ice dams. The result is water backing up under the roof shingles where it can soak through the roof decking or wall sheathing, causing damage to attics, ceilings and walls. There are three ways to prevent and defend against the damage due to ice dams: attic insulation and air sealing, proper balanced attic ventilation, and water-proofing shingle underlayment. All three work together.
Sealing bypasses (warm air leaks) from interior rooms to the attic is probably the most effective way to prevent ice dams. Bypasses are typically found around vent pipes, exhaust fans, chimneys, attic hatches, wall/ceiling framing joints, wiring and lighting fixtures. Use silicone caulk, poly plastic as fill material, foam sealant or a combination of all three to stop air flow around these areas.
Having a well insulated atticis an excellent way to increase energy efficiency and may slow down heat loss, but ice dams may still persist because warm air may bypass through insulation.
Not exactly an "ice dam," plugged or overweighted gutters can cause ice to build up and back up onto the roof. This condition can be remedied with electric heating cables. Once the gutter thaws, it should be refastened to slope correctly and should be cleaned out every fall.
A properly ventilated attic prevents moisture buildup by allowing air flow to carry out moisture. Although heat bypasses are the primary cause of ice dams, ventilation helps deter ice dams by keeping a cool even temperature on the inside surface of the roof.
Signs of inadequate ventilation include rusty nails or rust spots on insulation caused by moisture forming and dripping off nails, frost buildup during the winter, or possibly a lingering musty smell.
As a general guideline, half the vents should be at least 3' vertically higher than the draw vents and positioned as close to the eave as possible. A vent to attic space ratio of 1:300means 1 square foot of attic ventilation for every 300 square feet of space. Vents closer than 3' and no vapor barrier in the attic require a 1:150 ratio.
Passive venting refers to the unassisted, natural movement of air into and out of the attic. Using mechanical means like fans may be unreliable, waste energy, and at times draw in moisture and warm air.
Typically, passive venting is done by installing vents at the soffits that draw cool air in and vents near or at the ridge that allow warm, moist air to escape. Soffit vents should always be unblocked and insulation should be held back with baffles to permit unrestricted air flow.
This is the last defense. Waterproofing Shingle Underlayment is a very different kind of material. It is used in vulnerable locations on the roof deck that are most likely to leak during storms with high winds or when ice dams develop. Along the eaves, around roof penetrations and in the valleys are the area’s most likely to require waterproof underlayment. Manufacturers and roofing Contractors will not warranty roof leaks due to ice dams.
People are often mislead or confused by their roofing warranty, wrongly believing this is how long the new roof will last.