Building envelope testing in existing buildings
Existing buildings are tested under different protocols from new buildings, so testing must be approached from many different angles to achieve air tightness and better building performance.
- Understand the codes and standards that relate to air pressure testing.
- Know how to conduct a pressure test on an existing building.
- Understand alternative methods of testing for leakage in existing buildings
Air pressure testing of the building envelope or building enclosure is gaining traction in the industry due to the fact that air tightness of a building improves the building’s performance. For increased building performance, it is important to minimize the building’s air leakage to limit the negative impact it has on energy and indoor environmental quality (IEQ) issues within the building. The air pressure testing procedure for new buildings is fairly straightforward and has several testing standards to follow (see below), but testing of existing buildings is another matter. Existing buildings cannot be tested under the same protocols as new buildings, so you have to approach an existing building from many different angles to achieve the end goal.
To better understand the challenges of existing building testing, let’s review how new buildings are tested. To effectively test a new building, the first task is to specify under what standard the building will be tested and what acceptable leakage rate will be applied to the test. The main applicable testing standards are ASTM E779 and ASTM E1827, which are both residential standards. These standards have been used as the basis for U.S. Army Corps of Engineers (USACE) Air Leakage Test Protocol for Building Envelopes and the National Environmental Balancing Bureau (NEBB) Procedural Standards for Building Enclosure Testing, which are both standards for commercial building leakage testing.
For example, ASTM E 779 is a multipoint test that takes flow measurements at 10 different pressures from 10 Pa to at least 60 to 75 Pa. Under the ASTM E 1827 two-point method, you select two points with the low point being no greater than one-third of the high point and at least three times the baseline pressure. So for a USACE test using ASTM E 1827, you normally select 75 Pa and 25 Pa.
The basic process of pressure testing new construction is to test the whole building under both negative pressure and positive pressure at a maximum test pressure of either 50, 60, or 75 Pa. (ASTM E 779 is a multipoint test from 40 Pa to at least 75 Pa. For the single-point method of ASTM E 1827, you normally select your reference pressure of the leakage rate.) Normal leakage rates can vary from 0.10 to 0.40 cfm/sq ft of air barrier at test pressure.
Prior to testing, all intentional openings (such as exhaust fans, wall louvers, flues, and vents) are sealed. Sealing is normally achieved by using Visqueen and packing tape or carpet tack film to cover the opening in such a manner that the induced test pressure does not blow off the seal. All doors and windows need to have permanent weather seals and sweeps installed. A minimum of 10% of the ceiling tiles must be removed and all interior doors opened to assure a clear air path between the air barrier and the test fans.
Once the building is sealed, test fans and pressure manometers are installed to measure the leakage rate in accordance with the test standard being used. Before the leakage rate is tested, a building bias or baseline pressure is established by measuring the pressure differential between the interior and exterior of the space with the fans off and sealed. This pressure—which is created by either stack effect or wind pressures—will be used in the final test calculations. After the baseline test, the flow/pressure test is completed. The actual leakage test is run by measuring the leakage flow 10 times at each test pressure and using the average pressure and flow rate.
The test results will indicate if the air barrier leakage rate is below the selected leakage rate standard. To pass, the test must show a leakage rate below the standard leakage rate but must also indicate that the test results achieved at least a 95% statistical confidence level. (The accuracy of the test is dependent on the amount of variance between each pressure reading for both the baseline test and the test pressures. If they vary by more than 10%, the test will not be within the 95% confidence level.)