If you took a poll of building envelope and construction forensic experts, it's likely that moisture barriers would be high on the list of most poorly understood products used in wall assemblies. Besides deciding which type of barrier to use under various climate conditions, Building Teams must confront the nasty matter of how to install them correctly.
To shed some light on this nettlesome problem, we called upon Richard Robison, RA, CCS, NCARB, a principal at Lord, Aeck & Sargent, Atlanta, and a nationally recognized expert in construction specifications. In 2002 he was awarded the Construction Specifications Institute's Ben John Small Memorial Award for special proficiency and outstanding stature as a practicing specifier. He is a member of the AIA, CSI, the Southern Building Code Congress International, the Association for Preservation Technology International, the Masonry Society, and the American Society for Testing and Materials.
1 Understand the basic types of membrane primers and when each should be used.
Twenty years ago, when the first generation of so-called peel-and-stick membranes came out, rarely did they live up to their name. “They'd blow off with any wind pressure,” says Robison. Since then, manufacturers have developed primers to bond the “self-adhesive” sheets to the surface of the wall.
Mockup for a wall assembly for a new residence hall at Columbia Theological Seminary, Decatur, Ga. Building envelope expert Richard Robisonsays a standalone mockup like this should run about $10,000 in total costs but will save time and improve quality for the project. |
There are basically three kinds of primers: cutback asphalt, surface conditioners, and glues. Cutback asphalt is used primarily in colder climates, especially when the peel-and-stick is being applied when the temperature is below 40°F (something Robison stresses should be avoided if at all possible). Cutback asphalt is also used when VOCs are not a major concern, although there are water-based versions with low VOC ratings that could be used in projects seeking LEED or other green certification.
Surface conditioners are sealants that basically consolidate dust and close up the pores on the surface of the wall. “I'm not a particular fan of them because I don't think they have as good adhesion as other sealants,” says Robison. There are surface conditioners for use with concrete and masonry, another for plywood, and a third type for fiberglass-faced sheathing products. Surface conditioners should not be used when the temperature is below 40°F, he warns.
Glues can vary in their effectiveness, says Robison. “A lot depends on the reputation of the manufacturer and your own experience,” he says. “If the glue is working well and the phone isn't ringing, that's great, but if the membrane is curling or bubbling, it could look like a Laurel and Hardy comedy on the job site.” Again, don't use glue when it's below 40°F outside.
2 Firmly roll every square inch of transition membrane.
“It's of particular importance to roll every inch of the surface with a small roller, pressing the sheet into the primer and the substrate, and to keep going back and forth over the entire sheet—that point cannot be overestimated,” cautions Robison. He recommends installers use a four-inch-wide roller with a small handle. “It's laborious, it takes muscle, it's time-consuming, and it seldom gets done fully and properly,” laments Robison.
3 Be aware of special concerns about spray- and roller-applied weather barriers.
Over the last decade or so, manufacturers have come out with liquid-applied weather barriers. These barriers prevent the passage of air and liquid water and, depending on the formula chosen, they can be either vapor-permeable so as to allow moisture in the walls to dry in both directions, or they can be barriers to vaporous water as well. They are used in the field of the wall along with a peel-and-stick transition membrane at door, window, and louver openings—in fact, anywhere the wall system changes from one substrate to another. The liquids are rolled on with a paint roller or sprayed onto the wall.
Robison says these liquid-based systems have several advantages over peel-and-stick alone: 1) greater productivity, because there's no hand pressing, 2) greater adhesion, because the liquid can soak in and adhere well to the substrate under most conditions; and 3) after installation, you have either a vapor barrier or vapor-permeable membrane in service (depending on the liquid formula best suited for the project location; peel-and-sticks on the other hand are nearly always vapor barriers).
But there's a downside to using a spray system—the cost of buying or renting the equipment and keeping it cleaned and maintained.
Also, says Robison, you have to sequence the job correctly or you'll run into overspray problems. For example, you don't want to spray the windows, or any materials or equipment (such as a truck) underneath the spraying area. This is one reason why most installers prefer to roll the liquid on, rather than spraying it—there's just less risk of messing up.
Lastly, you need to be aware that manufacturers of liquid products have different formulas and application methods, which can affect the thickness of the final coat. Some use a two-component system, others a single-component material. Some require heat in the spray apparatus. Some are 100% solids content (liquids that undergo chemical change into a solid without losing solvents or volume in the process), so when your installer applies 60 mils of wet thickness, you end up with a 60-mil dry thickness on the wall; others are 50-75% solids, and 60 mils of wet thickness may only get you 45 mils of dry coating.
Controlling the mil thickness also depends heavily on the skill of the installer. “With some products you can easily see where it's too thin, but with some other products the color makes it hard to get a sense of the thickness,” says Robison.
There's even a difference of opinion as to how thick the membrane layer needs to be. Some manufacturers want it to be in the 45-60 mil range, some allow as little as 7-8 mils dry, while others say that as long as the membrane is continuous without pinholes or holidays there can be some variation in the thickness.
4 Build a mockup of the wall assembly.
“Construction detailing is so complex today, with so many trades focused on this one element, I recommend building a mockup on every project,” says Robison. “My experience with contractors, going back 35 years, is that if you tell them what you want, they will do it willingly, but not if you tell them after the fact.”
Robison says having a mockup invariably saves time and money in the long run. “Ten thousand dollars should buy you a foundation, the backup structural wall, the windows, the cladding, the weather barrier and its insulation, and the time of the people to build the mockup and evaluate it,” he says.
“Some owners and contractors see this as an extra cost. My feeling is this is penny-wise and pound-foolish. The various installers will be more productive on the entire job, and there will be fewer or no callbacks to plague the owner.”
One side note: Build the mockup separate from the structure itself. With a self-standing mockup, says Robison, you can play around with it and nobody cares; if it's part of the actual wall assembly, the temptation is to not mess with it, which defeats the whole purpose. Also, a standalone mockup is always there as a reference for the trades to check their work against.
5 Try to use sealing products from a single manufacturer, or at least products that are as compatible as possible.
In any wall assembly, you're going to have many different building products—perhaps a vinyl window, a steel lintel, metal panels, stone, brick, CMU, sheathing, insulation—each with its preferred method of protection against the weather, possibly each being installed by a different subcontractor. For the weather barrier you might have a peel-and-stick product for the through-wall flashing and a different peel-and-stick for use with the liquid barrier. Needless to say, making these disparate materials and products come together as a well-integrated wall assembly requires considerable knowledge, skill, and coordination.
At least for the weather barrier Robison recommends using a single manufacturer's products as much as possible. “The self-adhesive flashing and liquid-applied membrane need to be compatible,” he says. “But the weather barrier manufacturer's recommendations may be at variance with the window manufacturer's recommendations. You need to coordinate and resolve any disagreement.”
6 Follow the manufacturer's installation instructions, but keep your eyes wide open.
“Install in accordance with manufacturer's instructions” should be routine practice, but it is, sadly, a custom more honored in the breach than the observance. “These are all proprietary products, the formulas are different, although similar, and each manufacturer will have similar but slightly different installation instructions,” warns Robison.
For example, some manufacturers or independent consultants want you to use termination bars (metal strips used to support the sheet membrane) at the top of the window, others say do so on all four sides, and still others say you don't need termination bars at all. You have to use your best judgment and make your own decision.
The same goes for edge mastic, says Robison. Some weather barrier makers recommend using a slight bead on all edges of the membrane, even at lapped edges, while others do not require mastic at all. And some manufacturers recommend using a urethane caulk in one situation and asphaltic mastic in another.
Be aware, too, that certain manufacturers suggest various “levels” of installation—good, better, best—for their products. And for some manufacturers, says Robison, “their installation instructions are less than worthless, they have no tech support in the field, and all they sell is a product.” Which brings us to our next bit of advice.
7 Take advantage of the manufacturers' expertise.
“Get the manufacturers' technical representatives on the job site, consulting with you and the installer and reviewing the mockup,” says Robison. He says the major manufacturers are more than willing to do this, especially with a newly introduced product.
“I rely on good relationships with product manufacturers to achieve a comfort level,” says Robison. He recommends talking to the technical representative, product director, or product manager. “I can tell very quickly whether I'm talking with a sales guy or with someone who knows more about the technology than I do.”
The last word from this veteran of 35 years in the field: “Make sure the installers understand what you're after, and that you understand what they intend to do,” says Robison. “They'll do as you ask, as long as they know what you want.”
Related Stories
Wood | Nov 16, 2022
5 steps to using mass timber in multifamily housing
A design-assist approach can provide the most effective delivery method for multifamily housing projects using mass timber as the primary building element.
Giants 400 | Nov 14, 2022
4 emerging trends from BD+C's 2022 Giants 400 Report
Regenerative design, cognitive health, and jobsite robotics highlight the top trends from the 519 design and construction firms that participated in BD+C's 2022 Giants 400 Report.
Contractors | Nov 14, 2022
U.S. construction firms lean on technology to manage growth and weather the pandemic
In 2021, Gilbane Building Company and Nextera Robotics partnered in a joint venture to develop an artificial intelligence platform utilizing a fleet of autonomous mobile robots. The platform, dubbed Didge, is designed to automate construction management, maximize reliability and safety, and minimize operational costs. This was just one of myriad examples over the past 18 months of contractor giants turning to construction technology (ConTech) to gather jobsite data, manage workers and equipment, and smooth the construction process.
University Buildings | Nov 13, 2022
University of Washington opens mass timber business school building
Founders Hall at the University of Washington Foster School of Business, the first mass timber building at Seattle campus of Univ. of Washington, was recently completed. The 84,800-sf building creates a new hub for community, entrepreneurship, and innovation, according the project’s design architect LMN Architects.
Sponsored | Steel Buildings | Nov 7, 2022
Steel structures offer faster path to climate benefits
Faster delivery of buildings isn’t always associated with sustainability benefits or long-term value, but things are changing. An instructive case is in the development of steel structures that not only allow speedier erection times, but also can reduce embodied carbon and create durable, highly resilient building approaches.
Mass Timber | Aug 30, 2022
Mass timber construction in 2022: From fringe to mainstream
Two Timberlab executives discuss the market for mass timber construction and their company's marketing and manufacturing strategies. Sam Dicke, Business Development Manager, and Erica Spiritos, Director of Preconstruction, Timberlab, speak with BD+C's John Caulfield.
Green | Jul 26, 2022
Climate tech startup BlocPower looks to electrify, decarbonize the nation's buildings
The New York-based climate technology company electrifies and decarbonizes buildings—more than 1,200 of them so far.
Building Technology | Jun 9, 2022
GSA Green Proving Ground program selects six innovative building technologies for evaluation
The U.S. General Services Administration’s (GSA) Green Proving Ground program, in collaboration with the U.S. Department of Energy, has selected six innovative building technologies for evaluation in GSA’s inventory.
Smart Buildings | Jun 1, 2022
Taking full advantage of smart building technology
Drew Deatherage of Crux Solutions discusses where owners and AEC firms could do better at optimizing smart technology in building design and operations.
Sponsored | BD+C University Course | May 10, 2022
Design guide for parapets: Safety, continuity, and the building code
This course covers design considerations for parapets. The modern parapet must provide fire protection, serve as a fall-protective guard, transition and protect the roof/facade interface, conceal rooftop equipment, and contribute to the aesthetic character of the building.