Inspecting for Air Sealing Exhaust Fans

by Nick Gromicko, Katie McBride and Kate Tarasenko
Originally published at NACHI.ORG

Exhaust fans are typically installed in bathroom ceilings and in kitchen range hoods, or sometimes in kitchen ceilings or walls, to provide spot ventilation. Generous holes are typically cut in the ceiling drywall for installation of bath exhaust fans and kitchen exhaust fan ducts, leaving gaps where the fan box or duct is installed. While these gaps may be covered by decorative trim (in the case of exhaust fan boxes) or be hidden in cabinets (in the case of range hood exhaust fan ducts), those coverings will not stop air leaks.  Home inspectors should take note that when the drywall is not sealed to the edges of ducting or exhaust fan boxes (which themselves may be leaky), a considerable amount of conditioned air can leak through these gaps and into the unconditioned attic space, which can create air pressure imbalances, leading to a host of secondary issues related to energy efficiency and comfort.

Pressure and temperature differences between conditioned and unconditioned spaces encourage air flow where these leaks occur. Such air leakage represents energy loss; it could also potentially allow warm, moisture-laden air into unconditioned attics, where it can condense on cold surfaces, creating moisture problems, including mold growth. Air barriers need to be continuous in order to be effective; this means sealing all penetrations in exterior walls, ceilings, and floors adjoining unconditioned spaces.

Homeowners should make sure that the work of sealing around exhaust fans and ducts is performed after the fans and drywall have been installed. The responsibility for sealing air leaks around exhaust fans and ducts should be included in the contract for the appropriate trade (depending on the workflow at a specific job site for new-construction homes).

How Professionals Air Seal Holes Around the Kitchen Exhaust Duct

1. Openings for the duct should be cut that are no bigger than needed to fit the exhaust duct through the ceiling or top of the kitchen cabinet. Cuts should be clean and even.

2. After the exhaust duct is installed, air seal with caulk between the duct and drywall from the room side. If gaps are larger than a ¼-inch, use canned spray foam, applied carefully. Do not use pieces of fibrous insulation, which does not effectively air-seal. If the gaps are larger than 1 inch, they can be sealed from the attic side with air-blocking material, such as rigid foam that is cut to fit and sealed in place with caulk or spray foam. 

3. Use caulk or pre-made exterior wall gaskets to air seal the exterior fan duct vent to the exterior wall. Ensure that exterior gaskets are properly integrated with the house-wrap.

How Professionals Air Seal the Bathroom Fan Housing

1. Cut openings in the ceiling that are no bigger than needed to fit the fan box. Make clean, even cuts in the drywall.

2. After the fan is installed, air seal with caulk between the fan housing and drywall from the room side before installing the trim.

3. If any gaps are larger than a 1/4-inch, use canned spray foam, applied carefully, so that the trim will fit over it.

4. If any gaps are larger than 1/2-inch, they can be sealed from the attic side with air blocking material, such as rigid foam that is cut to fit and sealed in place with caulk or spray foam.  Do not use pieces of fibrous insulation, which does not effectively air-seal.

5. Seal holes in the fan housing with caulk or metal tape.

6. Use caulk or pre-made exterior wall gaskets to air seal the exterior fan duct vent to the exterior wall. Ensure that exterior gaskets are properly integrated with the house-wrap.

How Professionals Create an Insulation Shield for the Exhaust Fan

The bathroom exhaust fan box may have air leaks and holes in the casing. The fan should be covered to stop air leaks and to allow for the installation of insulation over it.

1. Create a five-sided box from a solid air barrier material, such as rigid foam, gypsum board or plywood. Tape the seams of the box with house-wrap tape (not duct tape) or seal it with mastic. Cut an access in the box for the exhaust duct.

2. Seal the box to the ceiling gypsum board and seal around the exhaust duct with caulk or canned spray foam.

3. Cover the box with attic insulation.

Summary

Exhaust fans are typically installed in bathroom ceilings and in kitchen range hoods, or sometimes in kitchen ceilings or walls to provide spot ventilation. If the space between the exhaust fan and the surrounding drywall is not properly sealed, large amounts of conditioned air can leak through, which can lead to energy loss and moisture problems. Homeowners should make sure that their contract includes this sealing work and that it's done after the installation of the exhaust fans. Home inspectors should check for air leaks in these potential trouble spots.

Don't forget to check out our last blog article about crawlspace hazards.

Inspecting the Crawlspace Hazards

by Nick Gromicko
Originally published at NACHI.ORG

Crawlspaces are host to a large number of conditions that may harm the house or inspectors. Never enter a crawlspace without proper personal protective equipment.

Crawlspaces are notorious for the nasty discoveries made there by inspectors, and it isn't hard to figure out why; for one thing, their cool, dark environment attracts undesirable pests and can promote dangerous conditions. And since crawlspaces are mostly unmonitored, hazards can breed there unchecked for long periods of time. The following are some of the more common dangers discovered in crawlspaces:

• mold and fungus. Just like pests, mold and fungus can grow rapidly in crawlspaces. They are both a health concern as well as a cause of wood decay, which can require a costly repair. Airborne mold spores can potentially enter the living space from the crawlspace. Molds produce allergens (substances that can cause allergic reactions), irritants and, in some cases, potentially toxic substances called mycotoxins. Inhaling or touching mold or mold spores may cause allergic reactions in sensitive individuals. Allergic responses include hay fever-type symptoms, such as sneezing, runny nose, red eyes, and skin rash (dermatitis). Homes infected with molds and fungus are also much more difficult to sell, often requiring costly remediation prior to closing the deal.
• pests. Dirt crawlspaces provide the environment that is enjoyed by ants, termites, and various other pests. Termites cannot survive long outside of their mud tubes, which you may see on foundation walls and piers. Carpenter ants should be plainly obvious as well, and both of theses pests can cause structural damage. Also bear in mind that where there are pests, there may also be pesticides, perhaps improperly applied, which is one reason why you should not enter crawlspaces without personal protective equipment. Snakes, spiders, bees and scorpions may also be lingering in the crawlspace, and while they pose little structural danger to the house, they certainly can harm you! Rapid retreat there can be difficult, so be cognizant of escape paths.
• hantavirus. Crawlspaces are perhaps the most likely sites in houses where hantavirus may be found. This is partly due to the fact that rodents that carry the pathogen are attracted to areas that are undisturbed by humans. Also, crawlspaces are generally dark places that lack ultraviolet (UV) radiation, which can rapidly inactivate the virus. Exposure to hantavirus may lead to Hantavirus Cardiopulmonary Syndrome (HCS), characterized by headaches, fever, difficulty breathing and, often, death. There is no known cure, vaccine or treatment that specifically targets HCS. However, if the symptoms are recognized early, patients may benefit from oxygen therapy.
• asbestos insulation. Do not disturb asbestos! The microscopic fibers that cause illness become airborne when the insulation is handled or disturbed, and if it appears to be in good shape, it might not be a problem at all. Prolonged exposure to asbestos insulation can cause mesothelioma, which is a cancer of the lining of the chest and the abdominal cavity, as well as asbestosis, in which the lungs become scarred with fibrous tissue.
• standing water or sewage.  Dirt crawlspaces are susceptible to water seepage, which can create a host of problems, such as microbial growth, odors, damage to stored belongings, and risk of electrical shock.
• structural collapse. If the home itself is unstable, it might be dangerous to enter its crawlspace. It is easy to become pinned, trapped or even crushed by unstable crawlspaces. Make sure someone knows that you are inspecting the crawlspace before you enter it.
• improper wiring. Watch for loose wiring, open junction boxes, or wiring that has become loose and fallen to the floor. 
• source of energy waste. Traditionally, crawlspaces have been vented to prevent problems with moisture, and most building codes require vents to aid in removing moisture from the crawlspace. However, many building professionals now recognize that ventilated crawlspaces allow a great deal of heat loss in the winter and moisture intrusion in the summer from moist air.

In summary, inspectors should expect to encounter a number of dangerous conditions in crawlspaces, so they should take proper precautions before entering them.

We invite you to check out our last blog article about housewrap.