An air gap in a drainage system is the unobstructed vertical distance of free space between the outlet of the waste pipe and the flood-level rim of the receptacle into which the waste pipe is discharging. As an example in a commercial restaurant, the air gap would be between the drainpipe of a salad bar and the floor sink or tub drain.

Hot water boilers should be provided with expansion tanks. There are two types of expansion tanks designated for use with a residential boiler system. A non-pressurized tank is simply a cylinder filled with air set at atmosphere pressure. A pressurized tank is a sealed cylinder divided by a flexible diaphragm. An expansion tank provides space for the water to expand as it is heated, and it keeps the water pressure within the normal operating range while the boiler is working. Thank you www.nachi.org

Water circulating through a hot water circulation system becomes chemically inert and does not rust the piping. But water heaters have a constant supply of fresh water with lots of corrosion-causing oxygen. Because of this, water heaters are prone to corrosion. As a result, water heaters usually have an anti-corrosion rod or sacrificial rod installed. Sacrificial anodes are typically made of magnesium or aluminum. The rod is immersed inside the water heater tank, allowing the chemical reaction from the fresh water to attack it rather than the tank. In some areas, rods are replaced regularly.

Whirlpool/jetted bathtub fixtures must be installed according to the manufacturer’s recommendations. The bathtub may be filled with water and tested during the rough-in plumbing inspection.

Discharge, Loop and Air Gap

The dishwasher discharge hose should be connected to the waste tee or disposer inlet above the drain trap. It is recommended that the drain hose either be looped up and securely fastened to the underside of the counter, or be connected to an air gap.

The illustration above shows the difference between an S-trap and a P-trap. S-traps are not permitted due to siphoning problems. Complements of www.nachi.org

Unvented Crawlspaces

In most climate zones, conditioned crawlspaces perform better than vented crawlspaces in terms of safety, health, comfort, durability, and energy consumption. Research has demonstrated how these conditioned crawlspaces also do not cost more to construct than vented crawlspaces. Crawlspace venting is a widely accepted business practice across the U.S. However, in humid climates, the warm humid air entering the crawlspace is more likely to condense on crawlspace framing than it will to help dry out the crawlspace. This is because the outside air can often have a dew point that is higher than the interior crawlspace framing surface temperature. As evidence, existing vented crawlspaces have experienced serious moisture and mold problems, costing builders and homeowners significant resources to repair.

Crawlspaces

Access openings must be a minimum of 18 inches high by 24 inches wide. Access to all under-floor spaces must be provided with access openings through the floor not smaller than 18 inches by 24 inches (457 mm by 610 mm).

Check for downspouts diverters not discharging water far enough away from the house. Check floor lawn irrigation systems spraying water against the house foundation, and check for gardens or planters that are up against the house. These may be causing wet soil pressure problems for the structure.

steep slope

The home inspector should note if a home is on a steep slope and, therefore, subject to erosion or movement. The maximum slope of a lot should be roughly 1-in-2.