Certified Irrigation Contractor (CIC)

Correct: Closed-cell spray foam and specialized gaskets are recognized as effective air sealing materials because they create a physical, airtight seal. Unlike fibrous insulation, these materials are non-permeable to air and can conform to the uneven surfaces typically found at the junction of a foundation and a sill plate, effectively stopping convective heat transfer and the movement of moisture-laden air.

Incorrect: Fiberglass batts are air-permeable and function as a filter rather than an air barrier, making them ineffective for air sealing. Vapor retarders are designed to limit moisture diffusion through materials but do not necessarily stop air leakage unless they are specifically detailed as part of a continuous air barrier system. Increasing R-value addresses conductive heat transfer but does not mitigate the convective heat loss or moisture risks associated with air infiltration and exfiltration.

Takeaway: A continuous air barrier requires materials that physically block air flow and can be sealed tightly at transitions and junctions between different building components.

Correct: Active sub-slab depressurization (ASD) is the most effective method because it addresses the root cause of radon entry: pressure differentials. By using a dedicated fan to pull air from the soil or crushed stone beneath the slab, the system creates a vacuum (negative pressure) relative to the house. This ensures that any air movement occurs from the house into the soil, rather than soil gases being drawn into the house by the stack effect or mechanical depressurization.

Incorrect: Increasing mechanical exhaust in upper levels can actually worsen the problem by further depressurizing the lower levels of the home, which increases the suction of soil gases through the foundation. High-permeability vapor retarders are designed to let water vapor pass through and do not provide the airtight seal necessary to block radon. Sealing visible cracks is a helpful supplementary step, but it is insufficient as a standalone solution because radon can enter through microscopic pores in concrete, floor-to-wall joints, and other hidden bypasses.

Takeaway: The most effective radon mitigation strategy is to manage the pressure boundary by ensuring the soil beneath the foundation is at a lower pressure than the interior living space.

Correct: Interstitial condensation is primarily driven by air leakage (convection) carrying water vapor into the wall cavity where it meets cold surfaces like the exterior sheathing. By ensuring a continuous air barrier, the auditor addresses the most significant moisture transport mechanism. Additionally, keeping the sheathing temperature above the dew point (often through exterior insulation) prevents the phase change of vapor into liquid water.

Incorrect: Increasing the R-value of air-permeable insulation like fiberglass batts without an air barrier can actually increase condensation risk by making the exterior sheathing even colder. Placing a Class I vapor retarder on the exterior in a cold climate is a fundamental error that traps interior moisture inside the wall assembly, leading to rot. While weep holes help with liquid water drainage in rainscreen systems, they do not address the physics of vapor condensation caused by interior air leaking into the assembly.

Takeaway: Controlling interstitial condensation requires a combination of air leakage prevention and thermal management to ensure building components remain above the dew point temperature of the interior air.

Correct: In building science, the ‘house as a system’ approach dictates that as we seal the building envelope to improve energy efficiency, we reduce the natural air changes per hour (ACH). This reduction means that pollutants generated inside the home—such as combustion gases (CO, NO2) from appliances, Volatile Organic Compounds (VOCs) off-gassing from building materials or furniture, and biological contaminants (mold, allergens) fueled by interior moisture—are no longer diluted by fresh air and can accumulate to levels that impact occupant health.

Incorrect: The suggestion that pollutants are primarily driven by outdoor ozone reacting with insulation is incorrect, as the primary concern in weatherized homes is the accumulation of indoor-sourced contaminants. The claim that insulation filters VOCs or combustion gases is false; insulation is not a substitute for proper source control or ventilation. Finally, the idea that biological pollutants require high air leakage to thrive is backwards; mold and dust mites typically thrive in tight, poorly ventilated spaces where high relative humidity is trapped.

Takeaway: Tightening the building envelope without providing managed ventilation increases the risk of health issues by allowing indoor-generated combustion byproducts, VOCs, and biological contaminants to concentrate.

Correct: Building science dictates the principle of ‘build tight, ventilate right.’ When air sealing reduces the amount of accidental air leakage (infiltration), the building no longer relies on these leaks for fresh air. If mechanical ventilation is not adjusted to provide the necessary air changes per hour, pollutants such as CO2, VOCs, and water vapor accumulate, leading to poor IAQ and potential health issues for occupants.

Incorrect: The idea that insulation alone slows air exchange is a misconception; while some insulation types reduce airflow, the primary issue here is the lack of controlled ventilation to replace the lost infiltration. Vapor diffusion is driven by vapor pressure differentials and is a separate mechanism from the bulk air movement addressed by air sealing. The stack effect is actually weakened, not intensified, by sealing the building envelope, as it restricts the pathways for air to enter at the bottom and exit at the top.

Takeaway: Effective air sealing must be paired with managed mechanical ventilation to ensure that indoor air quality is maintained as natural infiltration is reduced.

Correct: Air leakage facilitates convective heat transfer, which is the movement of heat via a fluid (air). When air can move freely through gaps and cracks (thermal bypasses), it carries heat around or through the insulation. This process effectively ‘short-circuits’ the insulation, meaning the high R-value of the material is not realized because the heat is not being forced to conduct through the material itself.

Incorrect: The idea that air movement improves conductive properties through compaction is incorrect; while settling can occur, it does not explain the failure of the thermal boundary in the presence of leaks. Radiant heat transfer is the transfer of energy through electromagnetic waves and is not the primary mechanism affected by air leakage. Vapor diffusion is a separate moisture transport mechanism and does not ‘stop’ heat transfer resistance in the manner described.

Takeaway: Insulation is only effective when it is coupled with a continuous air barrier to prevent convective bypasses from undermining the material’s R-value.

Correct: Balanced ventilation systems, including HRVs and ERVs, are designed to provide a controlled amount of fresh air while removing an equal amount of stale air. This approach is ideal for tight building envelopes because it maintains a neutral pressure balance, preventing the house from becoming significantly pressurized or depressurized, which could otherwise lead to moisture issues or combustion safety concerns.

Incorrect: Exhaust-only systems create negative pressure (depressurization), not positive pressure, and can pull in pollutants or soil gases. Supply-only systems create positive pressure, which can force moist indoor air into wall cavities, leading to interstitial condensation. Natural ventilation is not a reliable or controlled strategy for high-performance homes and does not involve vapor retarders as a means of air exchange; vapor retarders are intended to slow moisture movement, not facilitate air flow.

Takeaway: Balanced ventilation is the preferred strategy for tight homes because it manages air exchange rates and pressure differentials simultaneously while improving energy efficiency through heat recovery.

Correct: Air leakage (convection) is the primary mechanism for moisture transport into wall cavities. Even if a vapor retarder is present to stop diffusion, air bypasses through unsealed penetrations, electrical outlets, or top plates allow warm, moist indoor air to reach the cold exterior sheathing, where it cools below its dew point and condenses.

Incorrect: Vapor diffusion is a much slower process than air leakage and is effectively stopped by a standard vapor retarder. Reverse vapor drive typically occurs in warm, humid climates when sun-heated exterior cladding pushes moisture inward. Increasing the R-value of insulation makes the exterior sheathing colder, which increases the risk of condensation, but it does not lower the dew point temperature of the air itself.

Takeaway: Air leakage is a significantly more powerful transport mechanism for moisture than vapor diffusion and is the leading cause of interstitial condensation in cold climates.

Correct: Thermal bridging occurs when highly conductive materials, such as steel or concrete, create a path of least resistance for heat to bypass the insulation layer. This significantly lowers the ‘effective’ R-value of the entire wall or roof assembly compared to the ‘nominal’ R-value of the insulation alone. Furthermore, because these bridges conduct heat so efficiently, the interior surface of the bridge can become significantly colder than the surrounding surfaces in winter, potentially reaching the dew point and causing condensation, which leads to mold or structural damage.

Incorrect: Option B is incorrect because thermal bridging is primarily a conductive heat transfer mechanism, whereas air infiltration is a convective mechanism; while penetrations can cause air leaks, the term ‘thermal bridging’ specifically refers to the conductive path. Option C is incorrect because thermal bridging does not change the material properties (permeability) of the vapor retarder itself, though it does influence where moisture might condense. Option D is incorrect because thermal bridging is a phenomenon of conduction through solids, not radiant heat transfer, and it absolutely affects the effective conductive R-value of the assembly.

Takeaway: Thermal bridging significantly degrades the effective R-value of a building assembly and increases the risk of moisture-related damage due to localized cold spots.