Winooski School

Title: Winooski School

Award Category: Commissioning

Project Address/Location

60 Normand Street

Winooski, Vermont 05404
United States

Submitted By: Paul D'Amore

Company Info

BVH Integrated Services, a Salas O'Brien Company

One Gateway Center #701

Newton, Massachusetts 02458
United States

6172277133

[email protected]

Project Description and Background: This project was a major renovation and addition to an existing school in Winooski, Vermont. The existing building was 142,000 square feet and was first built in 1957, with five different additions constructed between 1964 and 2000. For this project 5 more additions would be added totaling 76,000 square feet, in order to accommodate all Winooski Public School students from elementary school to high school. During construction the school was continuously occupied, therefore construction was phased over 19 different phases. One of the primary reasons why envelope commissioning was specified for this project was the air leakage requirements. At the start of this project in 2020, the state of Vermont had just adopted a new commercial energy code requiring the whole building to have an air leakage rate below 0.30 CFM/sf @ 75 pascals. This is the first time that any state in New England had a code requirement for air leakage. However, because of our previous work commissioning and testing high performance air barriers, we had experience meeting similar air tightness targets. In addition to the code required whole building target, the utility sponsored program, Efficiency Vermont, required the two larger additions to have an air leakage rate below 0.15 CFM50/sf (guarded) and 0.20 CFM50/sf (unguarded), in order to receive energy efficiency incentives. To meet these requirements, we needed to assure that the air barrier on the new construction was getting properly installed and all air leakage paths between new and existing construction would be sealed.

Scope: Our role for this project was Envelope Commissioning and Testing Agent. We provided construction phase commissioning services including coordination meetings with the envelope subcontractors, envelope progress inspections and issue tracking, air barrier progress testing, and blower door testing. The methodology for determining the scope on the project was to periodically test and inspect the major envelope transitions for air tightness, to ensure each area would meet the code required target before the culmination of the blower door test. Because of the air tightness requirements, it was critical that a method was developed to verify the air barrier installation during the construction process while repairs could still be made. This applied to both new construction and the renovation of existing construction. From our experience, the best way to verify airtight assemblies while construction was ongoing is using pressurized fog per ASTM E1186. Other methods like ASTM E783 can also be used to provide quantitative data to assure the air barrier is meeting the target on individual assemblies but there were dozens of common air barrier assemblies to test and this methodology is slow and expensive. We opted instead to use pressurized fog. With it, we can test an assembly, such as a wall to roof transition, or an air barrier transition from a new wall to the existing construction, in about 15 minutes. The method quickly identifies the exact location of air leaks in an assembly and it is a visual tool to help the construction team “see” air leaks and better understand how to repair them. Traditionally pressurized fog testing per ASTM E1186 takes a lot of preparation to test even a small sample size. A chamber is built on one side of the tested detail, then it is filled with fog and pressurized using a motorized fan. However, building a chamber can be time consuming and difficult depending on the detail complexity and stage of construction. That means that even when pressurized fog testing is included in the project, it’s usage is often limited, and the more complex details do not get tested. We developed a unique method that pressurizes the fog as it is being dispensed which eliminates the need to build a pressurized chamber. The idea is simple; a fog generator is placed inside a pressurized compartment, and the fog is blown through a tube directed at the assembly being tested. In other words, the fog itself is under velocity pressure as it impinges the surfaces in question. If there is a breach in the surface, fog pushes through it to the other side where it can be seen. This method allows us to test much larger sample sizes and more complicated details in a fraction of the time it takes to build and pressurize a chamber. We can verify the air barrier performance of eight to twelve isolated details or assemblies in a day versus only three to four through the methods described above.

Solution: The addition walls utilized the DensElement system made by Georgia-Pacific, which at the time was only about five years old. The advantage of this system is that the air and weather barrier is factory applied to the sheathing, which can save time and money on labor and materials. However, all penetrations, sheathing joints, and transitions to other air and weather barrier materials still need to be sealed in the field, so the same level of dedication is needed to ensure the air and weather barrier are continuous. It could otherwise be easy for a new installer to forget that the sheathing is serving a dual purpose, leading to deficiencies where air and water leakage could occur. The exterior walls of the existing building’s are brick and CMU block with little to no insulation and no continuous air barrier. Virtually no drawings of the original building existed, so the design team could only reference the building layers that were easily visible prior to demolition work. As a result, the details for how the new construction interfaced with the existing construction were not always fully developed. This lead to some uncertainty about the correct path and termination point of the air barrier, so a method was needed to determine if the existing construction was tight enough to meet current air leakage requirements. The pressurized fog test method we developed was used seven times over the course of 18-months of construction, both as a quality assurance tool for the new construction and a diagnostics tool for the existing construction. We were able to test ten or more details each time, and tested long runs of the wall-to-roof transition, the wall-to-foundation transition, new-to-existing expansion joints, roof penetrations, installed windows, and especially tricky interfaces between new and existing construction. Because we were easily able to test specific details early in the construction process, and document all repairs, by the end of the project we were confident that the whole building, a combination of new and existing construction, would meet its air barrier targets. Once the demolition had occurred, we were also able to use the pressurized fog to determine which existing transitions showed indications of air leakage, and to what extent. We then were able to provide recommendations for improving the air barrier to the entire team. The General Contractor would use our recommendations to develop an RFI, and the architect would respond and provide direction for repairs. This ensured that each issue was address and that the existing construction could be improved within the short time that it was exposed.

Value: Our method for pressurized fog testing added tremendous value for air barrier commissioning on this project. All other methods of air leakage quality control testing had limitations: chamber testing per E783 and E1186 is limited by the number of chambers that can be built, this usually reduces sample size. Infrared thermography is weather dependent, and there would not have been the necessary temperature differential when we tested in the summer months. Blower door testing couldn’t be complete prior to construction due to the school being occupied year round and the presence of asbestos which can be disturbed from blower door testing. Without using our method of pressurized fog testing there would have been no other way to provide quality assurance testing of the air barrier to level of effectiveness that we were able to provide. Per Vermont 2020 Commercial Building Energy Standard the air leakage target was set at 0.30 CFM 75/SF of shell. This is a tight target that much of the country is not used to. In comparison, the 2021 IECC air leakage requirement for commercial construction is 0.40 CFM 75/SF of shell. Through our help, the whole building, both existing and new construction, was easily able to meet this leakage requirement. The final whole building air leakage rate for this building was 0.20 CFM 75/sf. For two of the additions, Efficiency Vermont required an air leakage rate below 0.15 CFM50/sf (guarded) and 0.20 CFM50/sf (unguarded). Pressure balancing the addition and the existing building was not feasible, therefore the air leakage rate was measure unguarded. The first addition had an air leakage rate of 0.106 CFM50/SF. The second addition had an air leakage rate of 0.143 CFM50/SF. Therefore, both additions also met the target.

Project Images

Additional Info: Video 1 shows an overview of the project and construction Video 2 shows an example of our fog test process. A leak can be seen at the end of the video. This project has also won the Associated Builders and Contractors NH/VT Excellence in Construction Award

Documents

Videos