Is it true that ideally the air pressure outside the building should be slightly lower than the air pressure inside the building?

The correct statement is that ideally, the air pressure outside the building should be slightly lower than the air pressure inside the building. This condition is beneficial for a few key reasons.

Firstly, maintaining a slightly positive internal pressure creates a scenario where outdoor air is pushed out rather than drawn in. This helps prevent the infiltration of outside pollutants, dust, and moisture, which can be particularly important in maintaining indoor air quality. It's crucial for comfort and health within the building.

Secondly, a positive pressure can protect against water intrusion, especially in climates where rain or snow can compromise building envelopes. When the internal pressure is higher than the external pressure, the likelihood of water entering through openings, windows, or other penetrations decreases.

Moreover, this balance in air pressure is an important aspect of energy efficiency. A building with controlled pressure will often require less work from its HVAC system to maintain a comfortable indoor environment, leading to lower energy costs.

The relationship between indoor and outdoor air pressure is a foundation of effective building design and environmental control, which makes the answer of true the appropriate one.