The number one cause of water intrusion and why windows leak in buildings is incorrect window installation. As the popularity of using windows with nailing fins for both new construction and replacement projects grows, design professionals need to understand how these types of windows are correctly specified, installed, and tested. Generally, the windows themselves perform well, but problems can arise during the window installation step, when the contractor puts the window in the hole and seals the window in place.

“Why Windows Leak” reviews the industry standards of window installation and provides step-by-step instruction of the installation process. While designers and contractors do have options based on their personal preferences and project scope, this article focuses on the most commonly used installation method.

Standard Window Installation Methods

To prevent window leaks and other issues related to water intrusion, proper window installation is paramount. Windows should be selected and installed in accordance with the manufacturer’s installation instruction, although those are not always provided. In these cases, there are several window installation standards for various types of windows including ASTM E2112, “Standard Practice for Installation of Exterior Windows, Doors and Skylights,” and AAMA 100, “Standard Practice for the Installation of Windows with Flanges or Mounting Fins in Wood Frame Construction.”

According to the ASTM standard, there are four different methods for proper window installation with nailing flanges (A, B, A1, and B1) based on the order that the building products are installed and how the flashing is installed at the mounting flanges. Below are the standard installation methods:

Method	WRB Application	Flashing Application
A	Applied after the window installation	Applied over the face of the mounting flange
B	Applied after the window installation	Applied behind the mounting flange
A1	Applied prior to the window installation	Applied over the face of the mounting flange
B1	Applied prior to the window installation	Applied behind the mounting flange

While all four ASTM window installation methods are acceptable and will combat water instrusion, the most common method seems to be Method A1 due to construction scheduling. It is also the method recommended by AAMA. Each project is unique and you may find that one of the other installation methods is more appropriate to your project. Step-by-step instructions for window installation method A1 when using a sheet‐type building wrap water-resistive barrier can be found here.

Fighting Window Leaks

According to Aaron Seward, in his June 2011 article When It Leaks It Pours in ARCHITECT, “seventy (70%) percent of all building litigation is a result of water intrusion through the building envelope” and most of the water intrusion problems occur at openings in the building enclosure. With the growing use of finned windows in multifamily construction and small office buildings, the proper selection and installation of these types of windows is important. Design professionals must understand how finned windows are integrated with the water‐resistive barrier, flashing, and exterior cladding. Besides windows, a barrier can be created in nearby walls with sealants, tapes, and primer to form a water‐resistive barrier membrane. The substrate and membrane together will provide an air barrier.

Water Leakage Testing

Water leakage is tested according to ASTM E 331, “Standard Test Method for Water Penetration of Exterior Windows, Curtain Walls, and Doors by Uniform Static Air Pressure Difference,” and AAMA 501.1, “Standard Test Method for Metal Curtain Walls for Water Penetration Using Dynamic Pressure.”

Test pressures usually match those for air infiltration. The architect should take care to establish leakage criteria beforehand. Frequently acceptable criteria are water amounts appearing on interior sills small enough to not run off the mullion. The static pressure test is more common, but might give an optimistic result because the test procedure may suck glass against gaskets, making a better than expected seal. Dynamic testing, which may help reveal leaks that would occur under the buffeting conditions of variable winds, is particularly effective at operable sash.

For more on window performance, click here.

Risks of Water Intrusion

According to the Institute of Inspection Cleaning and Restoration Certification, water damage can be deceptive. Water is capable of finding its way—whether through poorly installed windows or by way of other means—into structural cavities, where it wreaks havoc. If it goes undetected, that moisture can cause damage over a long period of time. This damage, at the very least, can result in odors and possibly discoloration. Greater damage will surface when materials delaminate, shrink, split and further deteriorate to the point where the only solution is expensive repairs.

Finding Window Leaks

If you do have a water intrusion via a window, finding the source can help you understand why the window is leaking, and vice versa. According to American Leak Detection, there are two key places to inspect right away if you see a leak or any signs thereof:

• The meeting of the window edge and wall, both on the interior and exterior of the house
• The rubber seal between the frame of the window and the pane of glass

It is important to remember, the ALD says, that “[e]ven if the amount of water entering your home is small, more water could be stuck inside the wall itself, and this could lead to severe mold or structural damage,” so be thorough when examining leaks.

More Information About Window Selection

For more information, see the AAMA Window and Door Selection Guide:

“This guide has been prepared to assist architects and specifiers in selecting windows to meet the requirements for specific jobs and conditions. It covers all classes of windows: storm, interior insulating, residential, commercial, heavy commercial and architectural. Design considerations provide information of significant value in planning for the best use of windows; therefore, a description of the various types of windows is available and a discussion of their particular characteristics is also included. Plus, performance requirements, as recommended by AAMA. Basic test method details are also reviewed.”

The guide is downloadable by going to the AAMA catalog and looking up “WSG-11”.

Current subscribers, check out the latest update to AGS Online, “Why Windows Leak.”

Not a subscriber? Sign up here

Gutters and downspouts are common components on the majority of all residential and commercial buildings with steep slope roofs. But given their importance, why is it that architects and builders seem to fail to go through the process of designing this important storm water drainage element but leave them incorrectly sized, or even worse, not sized at all?

Perhaps it is because they ‘straddle the fence’ of architectural and plumbing components. While their design documentation is shown on architectural drawings and in specifications, their design requirements are found in the Plumbing Code, which is maintained and updated separately. In 2015, the International Plumbing Code was updated to reflect new knowledge on storm drainage providing the correct sizing of gutters and downspouts as well as new Code requirements.  With AGS online, we can help you to manage both architectural and plumbing components by providing up-to-date information on code requirements and calculations as well as architectural specifications.

Since 1932, Architectural Graphic Standards (AGS) has sought to provide architects with the most current design practices and standards. With the power of electronic online publishing, AGS Online is able to continuously update technical and design knowledge in an industry that cannot wait on traditional book publishing. “Gutters and Downspouts: Sizing Calculations” is the first of the AGS Online series and reflects the current standard of care in building design for this subject. It includes a step-by-step design process, ICC table and figures, and a sample design problem and solution.

Sorting Out Gutter Sizes

The simplest method for calculation of flow rates is the rational method equation. While not as sophisticated as other methods, it is the method most commonly used. Rational equation calculators can be found on the Internet, or the calculations can be easily performed manually. Calculating the proper gutter size for a project is done with a simple calculation: Q = cia, where

Q	=	Flow rate in gallons per minute
c	=	Rational method runoff coefficient
i	=	Rainfall intensity, inch per hour, converted to gallons per minute
a	=	Drainage area of the roof in square feet

Rational method runoff coefficient (c) is a function of the characteristic of the roof surface area. Some published guidelines recommend a coefficient of 0.75 to 0.95 for most roof surfaces; however, a conservative runoff coefficient of 1.0 is recommended, assuming an impervious roof membrane with 100 percent runoff.

Drainage area of the roof (a) is the portion of the roof that is served by the gutter. The drainage area is then expressed in square feet. If the roof has parapets or walls around all of it or a portion of it, the vertical walls will contribute to additional water on the roof. Therefore, one‐half of this wall area should be added to the roof area.

The resultant calculation (Q=cia) will be the flow rate for the roof design.

Gutter dimensions are selected from the Horizontal Gutter Sizing Table, based on the slope of the gutter to the downspout(s) and the gutter capacity based upon the roof flow rate, in gallons per minute.

Assessing Rainfall Intensity

To properly size gutters for installation, you need to know the local rainfall intensity. This is taken from charts in the Code based on data from the National Weather Service, National Oceanic and Atmospheric Administration for 100‐year rainfall in a 1‐hour duration, expressed in inches. Select the rainfall intensity for your building location from the figures located here. Then, convert from inches per hour to gallons per minute per square foot by multiplying the rain intensity in inches by 0.0104.

Here is an example of a rainfall intensity chart, in this case for the eastern United States:

The Importance of Gutter and Downspout Sizing

According to the houselogic blog, properly sized gutters and downspouts are an integral part of keeping water away from the foundation of a structure. If the gutters and downspouts are not sized and installed properly, it can lead to severe and expensive damage to the entire building.

How To Install Gutters

Properly sized gutters are not going to do their job if installed improperly, so keep these important notes regarding the design of gutters and downspouts in mind throughout the sizing and installation process:

• Continuous gutters may be formed at the installation site with cold‐forming equipment, thus eliminating joints in long runs of gutter.
• Gutters and downspouts are available in aluminum, galvanized steel, copper, and stainless steel. Consult manufacturers for custom materials.
• Girth is the width of the sheet metal from which a gutter is fabricated.
• Although all joining methods are applicable to most gutter shapes, lap joints are more commonly used. Seal all joints with mastic or by soldering. Lock, slip, or lap joints do not provide for expansion.
• Expansion joints should be used on all straight runs over 40 ft. In a 10‐ft section of gutter that will undergo a 100° temperature change, linear expansion will follow these coefficients of expansion (CE) and movements: aluminum: CE, .00128, movement, .15 in.; copper: CE, .00093, movement, .11 in.; galvanized steel: CE, .0065, movement, .08 in.
• Always keep the front of the gutter lower than the back.
• Use a minimum width of 4 in., except for canopies and small porches. The minimum ratio of depth to width should be 3 to 4 inches.
• Many custom shapes for gutters and downspouts are available; consult manufacturers’ design manuals.

Flat Roof Draining and Gutters

Scuppers that empty into a gutter may be integrated with a roof edge. The scuppers are soldered into a formed gravel‐stop fascia system. The suggested maximum scupper interval is 10 ft. The front rim of the gutter must be 1 in. below the back edge, and it should be below the nailers used to elevate the roof edge. The drip edge on the fascia should lap the back edge of the gutter a minimum of 1 in. The gutter must be free to move behind the fascia.

Current subscribers, check out the latest update to AGS online, “Gutters and Downspouts: Sizing Calculations.”

Not a subscriber? Sign up here.

Dennis J. Hall, FAIA, FCSI

The Student Edition of Architectural Graphic Standards (AGS) has been a staple of the architecture classroom for over 20 years.   Now, along with the new edition of this core textbook, there is Graphicstandards.com, a subscription-based, fully searchable online reference that provides unlimited access to the text, drawings, details, and tables found in the professional version of our print product.

To help you better understand the benefits of using the AGS textbook in combination with the new online reference, we asked Keith Hedges, editor-in-chief of the new AGS Student Edition text, to provide more detail on the benefits of integrating Graphicstandards.com into your classroom.

Q: How can I incorporate graphicstandards.com into my course activities?

A: We have an Instructor’s Manual available on the instructor companion website which includes sample lecture slides, exam questions, and projects available as individual .pdfs and editable .docx formats. Instructors can also utilize the thousands of AIA-endorsed details available on graphicstandards.com to quickly create course content by importing selected details, tables, figures, and text into PowerPoint lectures, tailor images to create examination questions, and provide clues as to what ready-to-edit CAD files may be needed for students to customize their final drawings.  The downloadable details are ideal to prepare the students for the new ARE 5.0 click-and-drag, hot spot, and case study, graphic-based question types.

Q: Are there any sample syllabi available for instructors?

A: Yes. Detailed sample syllabi covering various course types, such as technology and design studios, provide ideas on how to fully integrate the new AGS Student Edition (SE.) The new AGS SE is shown as a required text and provides the chapter and page numbers for associated readings. The course content can be paired with the rich AGS SE index to easily find associated content and images through the graphicstandards.com refined search filters.

Q: What benefits are there for students using graphicstandards.com in their coursework?

A: AIA endorsed standards provide a solid foundation for students to build upon.  While the standards are foundational elements, the students must bring in their own expertise and knowledge to bear when using and customizing details for their own academic needs.  Graphicstandards.com is a verified source that you can trust.

Q: How is graphicstandards.com beneficial to instructors and students as a research tool, particularly in the studio environment.

A: Graphicstandards.com is a powerful research tool with thousands of available details where students can quickly find solutions to design problems or research topics by using the advanced search filters with the aid of the book’s index. The graphic details in non-AGS texts are often lacking in number and quality, forcing students to explore within a domain of online resources from product vendors or unknown and unproven resources, which means that the details may be incomplete, inaccurate, or inappropriate for their building’s context. Finding resources in the vast online realm can be very overwhelming to students. Having the fully searchable database of AIA-endorsed details (downloadable in .dwg, .dgn, and .dxf formats) allows students to spend less time looking for credible sources and ensures they can focus their attention on projects and coursework instead of pouring through vast manufacturer websites or endless Google searches.

Q: Is there complimentary instructor access or discounted student pricing for graphicstandards.com?

A: Instructors receive a full year subscription with adoption of graphicstandards.com for their course and students receive free one-month access to graphicstandards.com with the purchase of any new print or eBook of Architectural Graphic Standards Student Edition, 12e.  A discounted student subscription rate is then available after the free trial expires.

Q: Does graphicstandards.com work on mobile devices like smart phones and tablets?

A: In addition to PC and MAC, students can design anytime and anywhere by accessing graphicstandards.com using portable devices while on the go, 24/7.

With both print and digital options available, we give you the power to teach your students in a multitude of ways, ensuring they can learn in the format they prefer.   As you can see, there are many benefits to adopting both Architectural Graphic Standards Student Edition and graphicstandards.com as an online tool for your classroom.  Visit www.graphicstandards.com/student-edition-page/ for more information and to request an examination copy of the new textbook and start your free one-month trial subscription.