Three manufacturing industry groups for residential and commercial doors and windows — the Fenestration Manufacturers Association (FMA), the American Architectural Manufacturers Association (AAMA), and the Window and Door Manufacturers Association (WDMA), have joined forces to create and release a new “standard practice" document for installing doors in the coastal environment. It's called, “Standard Practice for the Installation of Exterior Doors in Wood Frame Construction for Extreme Wind/Water Exposure" — or, for short, FMA/AAMA/WDMA 300-12.
You can purchase and download the new document for $75 (non-member price) at the AAMA Publication Store. Also available is a companion document that applies to windows instead of doors (FMA/AAMA 100-12, “Standard Practice for the Installation of Windows with Flanges or Mounting Fins in Wood Frame Construction for Extreme Wind/Water Conditions").
Is it worth it? Maybe. Both documents offer illustrated, step-by-step instructions for installing the manufactured components into the wall. Each document includes several alternatives, and covers situations where the housewrap is applied to the wall after the door or window is installed, as well as cases where the window or door goes in before the housewrap is applied. Compared to the all-too-common practice of stapling up the housewrap, cutting it out of the opening, nailing on the window fins, and calling it good, these documents certainly describe a more robust installation.
But builders or window and door installers may find that neither document will serve as a full construction specification. Carl Hagstrom, who has taught a hands-on course on window installation at the JLC Live conference for a number of years, points out that the AAMA documents don't mention a sloped sill for windows, or a back dam at the inboard side of a door (details which, in the case of wind-driven rain, could be critical to good performance). And he notes the pro forma language "See manufacturer's instructions for installation details" in the cap flashing detail. Comments Hagstrom, “In the 35 years I've been involved in construction, I have yet to see instructions come with cap flashing."
There's already an industry standard for door and window installation: “ASTM E2112 - 07 Standard Practice for Installation of Exterior Windows, Doors and Skylights," created by ASTM International (formerly the American Society for Testing and Materials). That ASTM standard is referenced in the International Building Code and the International Residential Code, starting with the 2006 code editions.
But even the ASTM standard has some gaps and inconsistencies, points out architect Robert Bateman, a consultant with engineering firm Simpson Gumpertz and Heger, who specializes in building exterior water management details. Bateman worked actively on the development of ASTM E2112, especially the door sill pan flashing details — and he took a close look at those details in an article for Interface magazine in April 2010 (“A Flash in the Pan — a Field Guide for Windows and Doors").
In Bateman's opinion, he writes, “ASTM E2112 can be easily reviewed by construction experts to find miscellaneous inconsistencies, some conflicts, and many unevenly developed sections." The building code is similarly unclear about what is and isn't required, he argues. Bateman's article supplies a useful, detailed review of some of those gray areas, including a close look at the height of the back dam that might be necessary to hold water out at the door sill in an episode of wind-driven rain. Bateman also examines the strategy of creating an air seal at the inboard edge of the sill pan, to deprive wind-driven water of its avenue into the moisture-sensitive components in the wall, or into the interior space.
For builders looking to limit their liability, a careful look at the AAMA “standard practice" documents and the ASTM standard are probably worthwhile — if only to gain a better familiarity with the way component manufacturers are likely to frame their arguments about who is to blame in the case of a failure. But for a builder who's looking to develop a robust building detail that is practical in the field and that will prevent water intrusion in the first place, Bateman's article may be a better starting point.
In a phone interview, Bateman said that the details in the AAMA documents owe their origins to particular conditions in South Florida — originally, he said, the industry group was concerned with the specific issues of installing windows in the houses built with concrete masonry block for the first story walls, with a second story of wood framing, and typically a stucco cladding applied directly to the block. The generic details that developed out of that narrowly focused starting point leave a lot to be decided, Bateman observes — especially if the construction or cladding details change. “All the specific parts and pieces make a big difference," says Bateman. “The type of window, the type of substrate, the type of cladding, whether it's stucco or siding, and where you put sealant joints, the water barrier you select…all of those have an effect."
In any case, Bateman points out, workmanship details can make all the difference. “A misplaced fastener can be the cause of a leak," he says. “The wrong sort of sealant, or sealant in the wrong place, could be the cause of a leak."
