Air Barrier Protects New Library Wing

Air barriers are now required on all commercial construction projects in Massachusetts. That state’s Energy Code Chapter 13 calls for barriers to control the movement of air and moisture into and out of buildings. Especially in regions with large seasonal temperature variations, air leakage throughout buildings may lead to increased heating and cooling loads, damage to building envelope components, occupant health or comfort issues, and wetting of materials. (See Safety Watch on page 16.) Wet materials and libraries do not mix.

The Boston architectural firm of Ann Beha Architects, Inc., drew up plans to make the enlarged building appear as though it had all been built in the early 20th century. But rather than solid brick walls to match the original construction, the library addition would complement the Georgian Revival design. The library addition would actually be constructed with problemsolving modern materials-inner walls with brick exterior cladding separated by an air cavity. When it came to the air barrier system, Ann Beha Architects wanted the best. With dozens of different systems to choose from, they decided upon a fluid-applied approach.

“We specified an air barrier membrane for use in the brick cavity wall,” said architect Brent Stringfellow. “This system acts as both a moisture and vapor barrier, and is located on the warm side of the building. The system was chosen for its ability to contribute to a more energy-efficient building that will effectively minimize concerns about condensation with the exterior wall assembly.”

Stringfellow believes that fluid-applied air barrier systems are superior to more traditional moisture barriers (including sheathing, or roll-on adhesive-backed barriers), which have numerous installation difficulties and are prone to condensation issues in such installations.

Air barrier contractor Gleeson Powers Inc. (GPI), of Franklin, Massachusetts, won the bid to lay down Tremco’s ExoAir 120 Fluid-Applied Air & Vapor Barrier Membrane atop Dens Glass installed by the general contractor G&R Construction. ExoAir 120 is a monolithic (seamless) elastomeric membrane system designed to be sprayed on to exterior above-grade walls to prevent air infiltration and exfiltration.

Depending upon the amount of work to be done, a two- to six-man crew worked on this four-month project. The work could have been performed in about half that time if coordination between other trades wasn’t necessary. “We weren’t on the project all the time,” said project manager Dana Arsenault. “How fast we got our job done was determined by how fast the other contractors closed their parts of the building.”

It was GPI’s duty to ensure everyone worked together.

Few building construction components require the coordinated activities of more construction trades than air barrier systems. On this project, GPI, the roofer, the Dens Glass installer, and the mason had to coordinate. Sequencing was critical because each trade worked closely with the air barrier system.

A construction schedule was developed during the preconstruction meeting to ensure that the air barrier system was not compromised.

“The most important step is the pre-job meeting,” said Arsenault. “We meet with the general contractor, the roofer, the mason, and the exterior wall contractor. That meeting is the most important item in the whole process.”

The sole aim of that meeting is to get the other trades on board so they’re familiar with the air barrier system and they know what they need to do to provide correct tie-ins and wall flashings. Each job and each flashing system is different.

“Most often, masons follow our crew,” Arsenault said. “It is important they use care, especially if they utilize an anchoring system that penetrates the air barrier. If they miss the stud with a mechanical tie-in, they need to leave it. Don’t pull it out. The membrane seals around it. If they pull one out after missing a stud, they’ll leave a hole in the air barrier system.”

Failure to sequence the project effectively may lead to gaps showing up in the system at major joints such as roof-to-wall, and wall-to-foundation, as well as where wall junctions meet window and door frames. Incorrectly installed structural, mechanical, and electrical systems may also impede barrier continuity.

Thus, it was important for GPI to ensure the correct sequence of buildups involving different trades in different orders. GPI also relied on Tremco and the architect at different times to help give those trades proper direction to make sure the job proceeded smoothly and correctly.

“Constant communication prevents goof-ups such as the installation of incorrect flashing systems,” said Arsenault. “If a mason doesn’t get the word, he could install an incorrect flashing, leaving us with remedial work.”

Whether the building specs call for self-adhesive flashing, copper flashing, fabric flashing, or metal flashing, the flashing must match the overall system. The same holds true with tie-ins between the walls and the roofing system.

“It’s important to hash those things out beforehand to avoid mix ups,” Arsenault said.

To help the construction along, the townsfolk at Needham emptied the library and moved its contents to temporary quarters at High Rock School. The move gave the GPI crew great access to the construction site. GPI could drive their box van right up to the building. For the most part, they worked without fear of overspray. If conditions warranted, GPI could easily notify the general contractor to have all the construction workers move their trucks to the far side of the parking lot.

Even brand new construction requires intensive prep, and this job was no different. All the seams in the Dens Glass had to be filled with fiberglass reinforced tape. Gaps were filled with Tremco Vulkem 116 sealant. Transitions between substrates were achieved by applying ExoAir 110 and HOLT (low temperature) self-adhered air and vapor barrier membrane sheets.

On a typical day in which the full six-man crew worked, two men would construct transitional membranes and flashings. Two men would tape seams and fill gaps with caulking guns ahead of the spray crew. Two men would work on the spray rig—one on the nozzle and one minding the hose. Arsenault supervised the project and kept an eye on the spray equipment.

Using a Graco 733 airless with a #631 nozzle, the GPI coatings professionals laid down the ExoAir 120 from a distance of approximately 18 inches. They used multiple overlapping passes with a cross-hatch technique—alternating horizontal and vertical passes—to ensure even thickness and coverage.

The 60-mil WFT coat typically cured between 16 and 24 hours at 75°F at 50% relative humidity to achieve a 40-mil DFT coat.

“As a part of our quality control, we routinely test with a Nordson-Gardco wet-film thickness gauge,” said Arsenault (see “Scratching the Surface,” page 44). “In addition, once the material is sufficiently cured, we do a peel adhesion test to make sure we have an adequate bond.”

The black polymer ExoAir 120 comes in 55-gallon drums. The GPI coating professionals were careful to store the ExoAir 120 drums off the floor and to tightly seal open drums as per Tremco’s specifications.

For wintertime use, GPI makes sure they store ExoAir 120 at an ambient air temperature of 50°F or higher, and never allows it to freeze. They’ve applied it to substrates as cold as 40°F by preheating the drums using a heat exchanger piped into GPI’s box van’s radiator. The Ford F350 diesel’s engine must be kept running during the preheat. However, preheating was not required for this job.

GPI was also able to cospray the ExoAir 120 with a special accelerant — in this case a calcium chloride solution — to help it lay down better on vertical surfaces.

“Cospraying is a misting process that advances curing on vertical surfaces and helps to avoid sags and runs,” said Arsenault. “It’s basically another nozzle attached to the side of the Graco gun. The material comes out of a separate tank with its own pump, and comes out of the gun as a mist. What it does is draw the moisture out of the material to provide a quick cure.”

During the cospraying process, the accelerant mixes with the waterproof material “in-flight” prior to reaching the wall. This allows the membranes to set more quickly. It is important to note, however, that the accelerant does not change the nature of the single-component products being used.

Although the project didn’t present many unexpected problems, the design of the library addition created its own challenges. Some areas produced distinct obstacles when it came to providing a continuous air barrier system.

The library comprises numerous roof elevations and intricate wooden soffits at the top of the building. Tying the air barrier into the roof was difficult and required a great deal of care and coordination with the roofer. In addition to being fully tied-in, the sheet-applied ExoAir 110 self-adhered air and vapor barrier membrane had to be compatible with the roof membrane. Flashings had to be sequenced properly.

The trick was to make sure the GPI crew got to the wall before the roofer when they needed to, or after the roofer when they needed to, as the case dictated. After all, an air barrier is only effective when it is continuous.

“There were a lot of low walls and walls that ran from a low roof to a high roof,” Arsenault said. “It took a lot of coordination to make sure that our work with the general contractor and roofer went smoothly. Credit goes to our team for keeping sharp eyes on all of that to make sure nothing was left out.”

With the pages now closed on the Needham Library restoration project, the GPI crew is satisfied with their performance.

From the outside, the new library looks like a classic Georgian Revival brick building with zinc and copper siding. Library patrons can’t see the wall-within-a-wall or the monolithic air barrier that helps control the environment. Even though library patrons can’t see the results of GPI’s work, the library building itself is better off.

When effective air barrier systems are in place, the U.S. Department of Energy confirms that energy efficiency can be improved by as much as 40% while improving occupant comfort. As a result, the list of other states pushing to incorporate air barriers in their building and energy codes is growing.

“We’ve done a lot of public work over the years, and we take a lot of pride in everything we do,” said Arsenault.

His coatings team took control of their project by vigorously communicating with the other trades to make sure that, in the end, their product worked as advertised. They made use of the architect and supplier when needed to provide correct answers to technical questions. They made sure that every transition, tie-in, and overlap was perfect. They inspected their own work to make sure the city of Needham would get a library addition that would keep performing for years to come.

Even though the insides of the library walls will remain a mystery to most patrons, GPI knows the importance of the air barrier.

“It’s neat to drive by the library and watch happy-looking people go in and out, knowing you had a part in building it,” Arsenault said.