Backdrafting is the reverse flow of gas in the flues of fuel-fired appliances that results in the intrusion of combustion byproducts into the living space. Many fuel-fired water heaters and boilers use household air and lack an induced draft, which makes them especially vulnerable to backdrafting when indoor air pressure becomes unusually low. Inspectors should try to spot evidence of backdrafting in homes. 
How does backdrafting happen?
 
Fuel-fired water heaters, boilers, wall heaters, and furnaces are designed to exhaust the byproducts of combustion to the outdoors through a flue. These hot gases rise through the flue and exit the home because they are not as dense as indoor air. The pressure differential that allows for the release of combustion gases can be overcome by unusually low indoor air pressure caused by a high rate of expulsion of air into the outdoors through exhaust fans, fireplaces and dryers. When this happens, combustion gases can be sucked back into the house and may potentially harm or kill building occupants. Improperly configured flues or flue blockages can also cause backdrafting.
 
How can InterNACHI inspectors test for backdrafting?

• An inspector can release smoke or powder into the draft diverter to see whether it gets sucked into the duct or if it spills back into the room. A smoke pencil or a chemical puffer can be used to safely simulate smoke.   
  
  
• An inspector can hold a lighter beside the draft diverter to see whether there is sufficient draft to pull the flame in the direction of the flue. 
  
  
• Combustion gases that back-draft into a house may leave a dark residue on the top of the water heater. The presence of soot is an indication of backdrafting, although its absence does not guarantee that backdrafting has not happened. 
  
  
• A carbon monoxide analyzer can be used to test for backdrafting of that gas. Inspectors should be properly trained to use these before they attempt to use one during an actual inspection, primarily to avoid false negatives. 
  
  While performing the above-noted tests, it is helpful if inspectors ask their clients to turn on all devices that vent air into the outdoors in order to simulate worst-case conditions. Such devices may be dryers, or bathroom and kitchen fans.

Types of fuel-fired water heaters: 

• Atmospheric DraftMost backdrafting is the result of the characteristics of this type of water heater. Combustion gases rise through the ventilation duct solely by the force of convection, which might not be strong enough to counter the pull from dips in indoor air pressure. 

• Induced Draft
  This system incorporates a fan that creates a controlled draft. The potential for backdrafting is reduced because the induced draft is usually strong enough to overcome any competing pull from an indoor air-pressure drop.  

• Sealed Combustion
  The combustion and venting systems are completely sealed off from household air. Combustion air is drawn in from the outdoors through a pipe that is designed for that purpose. The potential for backdrafting is nearly eliminated because the rate of ventilation is not influenced by indoor air pressure, and the vented gas has no pathway into the home.

• Water Heater Location
  The installation of fuel-fired water heaters in particular household locations can increase the chances of personal harm caused by backdrafting. The 2006 edition of the International Residential Code (IRC) states the following concerning improper location:

Fuel-fired water heaters shall not be installed in a room used as a storage closet. Water heaters located in a bedroom or bathroom shall be installed in a sealed enclosure so that combustion air will not be taken from the living space.
In summary, inspectors should try to spot evidence of backdrafting.

Attic pull-down ladders, also called attic pull-down stairways, are collapsible ladders that are permanently attached to the attic floor. Occupants can use these ladders to access their atticswithout being required to carry a portable ladder.
 
Common Defects
 Homeowners, not professional carpenters, usually install attic pull-down ladders. Evidence of this distinction can be observed in consistently shoddy and dangerous work that rarely meets safety standards. Some of the more common defective conditions observed by inspectors include: 

• cut bottom cord of structural truss. Often, homeowners will cut through a structural member in the field while installing a pull-down ladder, unknowingly weakening the structure. Structural members should not be modified in the field without an engineer’s approval; 
• fastened with improper nails or screws. Homeowners often use drywall or deck screws rather than the standard 16d penny nails or ¼” x 3” lag screws. Nails and screws that are intended for other purposes may have reduced shear strength and they may not support pull-down ladders; 
• fastened with an insufficient number of nails or screws. Manufacturers provide a certain number of nails with instructions that they all be used, and they probably do this for a good reason. Inspectors should be wary of “place nail here” notices that are nowhere near any nails; 
• lack of insulation. Hatches in many houses (especially older ones) are not likely to be weather-stripped and/or insulated. An uninsulated attic hatch allows air from the attic to flow freely into the home, which may cause the heating or cooling system to run overtime. An attic hatch cover box can be installed to increase energy savings; 
• loose mounting bolts. This condition is more often caused by age rather than installation, although improper installation will hasten the loosening process; 
• attic pull-down ladders are cut too short. Stairs should reach the floor;  
• attic pull-down ladders are cut too long. This causes pressure at the folding hinge, which can cause breakage; 
• improper or missing fasteners;
• compromised fire barrier when installed in the garage;
• attic ladder frame is not properly secured to the ceiling opening; 
• closed ladder is covered with debris, such as blown insulation or roofing material shed during roof work. Inspectors can place a sheet on the floor beneath the ladder to catch whatever debris may fall onto the floor; and 
• cracked steps. This defect is a problem with wooden ladders. 
• In sliding pull-down ladders, there is a potential for the ladder to slide down quickly without notice. Always pull the ladder down slowly and cautiously. 

Safety tip for inspectors: Place an "InterNACHI Inspector at work!" stop sign nearby while mounting the ladder.
 Relevant Codes
The 2009 edition of the International Building Code (IBC) and the 2006 edition of the International Residential Code (IRC) offer guidelines regarding attic access, although not specifically pull-down ladders. Still, the information might be of some interest to inspectors. 
2009 IBC (Commercial Construction):
1209.2 Attic Spaces. An opening not less than 20 inches by 30 inches (559 mm by 762 mm) shall be provided to any attic area having a clear height of over 30 inches (762 mm). A 30-inch (762 mm) minimum clear headroom in the attic space shall be provided at or above the access opening. 
2006 IRC (Residential Construction):
R807.1 Attic Access. Buildings with combustible ceiling or roof construction shall have an attic access opening to attic areas that exceed 30 square feet (2.8m squared) and have a vertical height of 30 inches (762 mm) or more. The rough-framed opening shall not be less than 22 inches by 30 inches, and shall be located in a hallway or readily accessible location. A 30-inch (762 mm) minimum unobstructed headroom in the attic space shall be provided at some point above the access opening.
Tips that inspectors can pass on to their clients:

• Do not allow children to enter the attic through an attic access. The lanyard attached to the attic stairs should be short enough that children cannot reach it. Parents can also lock the attic ladder so that a key or combination is required to access it. 
• If possible, avoid carrying large loads into the attic. While properly installed stairways may safely support an adult man, they might fail if he is carrying, for instance, a bag full of bowling balls. Such trips can be split up to reduce the weight load. 
• Replace an old, rickety wooden ladder with a new one. Newer aluminum models are often lightweight, sturdy and easy to install. 

In summary, attic pull-down ladders are prone to a number of defects, most of which are due to improper installation.

​Backflow is the reversal of the normal and intended direction of water flow in a water system. Devices and assemblies known as backflow preventers are installed to prevent backflow, which can contaminate potable water supplies.
 
Why is backflow a problem?
Backflow is a potential problem in a water system because it can spread contaminated water back through a distribution system. For example, backflow at uncontrolled cross connections (cross-connections are any actual or potential connection between the public water supply and a source of contamination or pollution) can allow pollutants or contaminants to enter the potable water system. Sickness can result from ingesting water that has been contaminated due to backflow. 

Backflow may occur under the following two conditions:
back-pressure:
Back-pressure is the reverse from normal flow direction within a piping system as the result of the downstream pressure being higher than the supply pressure. This reduction in supply pressure occurs whenever the amount of water being used exceeds the amount of water being supplied (such as during water-line flushing, fire-fighting, or breaks in water mains).

back-siphonage:
Back-siphonage is the reverse from normal flow direction within a piping system that is caused by negative pressure in the supply piping (i.e., the reversal of normal flow in a system caused by a vacuum or partial vacuum within the water supply piping). Back-siphonage can occur when there is a high velocity in a pipe line, when there is a line repair or break that is lower than a service point, or when there is lowered main pressure due to high-water withdrawal rate (such as during fire-fighting or water-main flushing).
Atmospheric Vacuum Breakers 

Backflow prevention for residences is most commonly accomplished through the use of atmospheric vacuum breakers (AVBs). AVBs operate by allowing the entry of air into a pipe so that a siphon cannot form. AVBs are bent at 90 degrees and are usually composed of brass. Compared with backflow preventer assembles, AVBs are small, simple and inexpensive devices that require little maintenance or testing. They have long life spans and are suitable for residential purposes such as sprinkler systems. InterNACHI inspectors can check for the following:

• The AVB must be at least 6 inches above any higher point downstream of the device. For this reason, they can never be installed below grade. Even if they are installed 6 inches above grade, inspectors should make sure that they are not installed less than 6 inches above some other point in the system downstream of the device.
  
  
• The AVB cannot be installed in an enclosure containing air contaminants. If contaminated air enters the water piping, it can poison the potable water supply. 
  
  
• A shut-off valve should never be placed downstream of any AVB, as this would result in continuous pressure on the AVB. 
  
  
• AVBs cannot be subject to continuous pressure for 12 hours in any 24-hour period or they may malfunction. 
  
  
• Spillage of water from the top of the AVB is an indication that the device has failed and needs to be replaced. 

Types of Backflow Preventer Assemblies

Some types of assemblies are common in commercial and agricultural applications but are rare for residential uses. The appropriate type of backflow preventer for any given application will depend on the degree of potential hazard. The primary types of backflow preventers appropriate for use at municipalities and utilities are: 

• double check valves:  These are commonly used in elevated tanks and non-toxic boilers. Double check-valve assemblies are effective against backflow caused by back-pressure and back-siphonage and are used to protect the potable water system from low-hazard substances. Double-checks consist of two positive-seating check valves installed as a unit between two tightly closing shut-off valves, and are fitted with testcocks. 
  
  
• reduced pressure principle assemblies:  These are commonly used in industrial plants, hospitals, morgues, chemical plants, irrigation systems, boilers, and fire sprinkler systems. Reduced pressure principle assemblies (RPs) protect against back-pressure and back-siphonage of pollutants and contaminants. The assembly is comprised of two internally loaded, independently operating check valves with a mechanically independent, hydraulically dependent relief valve between them.
  
  
• pressure vacuum breakers:  These are commonly used in industrial plants, cooling towers, laboratories, laundries, swimming pools, lawn sprinkler systems, and fire sprinkler systems. Pressure vacuum breakers use a check valve designed to close with the aid of a spring when water flow stops. Its air-inlet valve opens when the internal pressure is one psi above atmospheric pressure, preventing non-potable water from being siphoned back into the potable system. The assembly includes resilient, seated shut-off valves and testcocks.

Requirements for Testers and Inspectors
A number of organizations, such as the American Water Works Association (AWWA) and the American Backflow Prevention Association (ABPA) offer certification courses designed to train professionals to test backflow preventers. Requirements for training vary by jurisdiction. Inspection of backflow preventers requires knowledge of installation requirements, although inspectors are not required to become certified.
In summary, backflow preventers are designed to prevent the reverse flow of water in a potable water system. They come in a number of different types, each of which is suited for different purposes.