Duct in a crawl space rests directly on the soil. What should the report note?

Ductwork resting on crawl space soil is in permanent contact with a moisture source. Metal duct corrodes from the outside in where it sits on damp earth, and flexible duct's outer jacket and insulation absorb moisture, lose R-value and support mould growth. Once corrosion perforates the duct or the jacket tears, the duct is open to the crawl space — and because supply ducts are pressurised and returns are under suction, that opening either loses conditioned air into the crawl or draws crawl space air, with its moisture, soil gas and odour, into the living space. The correct installation keeps duct up off the soil on hangers or supports at proper intervals, over a ground vapour barrier, which is why the inspector reports both the soil contact and the missing support.

Soil contact keeps the duct and its insulation continuously damp, which corrodes metal and degrades flexible duct jackets. A perforated or torn duct then exchanges air with the crawl space, either losing conditioned air or drawing crawl space moisture and odour into the house.

Ducts in crawl spaces must be supported clear of the ground at specified intervals, and crawl spaces should have a ground vapour barrier. Duct leakage in a crawl space exchanges air between the living space and the crawl, carrying moisture, soil gas and contaminants.

Ducts Hang, They Do Not Lie Down. Soil is a moisture source, not a support — and a wet duct becomes a leaking duct.

Connect the duct condition to indoor air. A leaking return in a damp crawl space is an air quality finding as much as an efficiency one.

• •Treating soil contact as adequate support
• •Overlooking that duct leakage in a crawl affects indoor air quality
• •Assuming ground contact has a neutral or beneficial thermal effect