Positive Building Pressurization - Why is it Important?

Garrett Holland / Jun 21, 2019

Building pressurization is a very important factor to consider in maintaining building health. A positively pressurized building means that in relation to the outdoors, the building is positive, or under normal operation, will push air from the inside to the outside if a door is open, or through any building opening. Building pressurization should be slightly positive compared to the outdoors. Ideally, a building’s pressure should be +0.02” w.c. to +0.05” w.c. greater than the outdoor pressure.

A negatively pressurized building means that in relation to the outdoors, the building is negative, or under normal operation, air will be sucked into the building through doors or other building openings. A negative building in the summer or winter months can cause serious problems, such as:

• High humidity (When untreated humid air is entering the building through doors or any other building opening). This could lead to mold growth and condensation to form on windows or other building surfaces.
• Cold drafts in the winter and hot spots in the summer
• Higher energy costs due to untreated air entering the building
• Difficulty maintaining temperature setpoints
• Potential for unwanted gasses to seep inside the building wherever air leaks are present

How do you avoid negative building pressurization? In order for a building to be positive, the amount of treated outdoor air passing through rooftop units, air handling units, and other building openings should be greater than the amount going out through exhaust fans or building penetrations. This outdoor air quantity should be calculated by an engineer, and setup by the test and balance contractor and/or the controls contractor.

Maintaining the integrity of the building envelope is also important. A leaking building is difficult to keep positive, and costs more money to cool or heat.

Keeping an eye on building pressurization will help the owner to save money, and maintain a safe and comfortable environment for tenants.