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Construction Techniques to Prevent Water Penetration at Windows

Windows, and their interface with the exterior walls, are an important part of a building’s envelope that resists the intrusion of water. Most builders take many precautions to protect a house from water damage. One of the most important factors in keeping the water out is the installation of window flashing, a thin material that prevents water from seeping in around a window. Over time, even a tiny gap around a window that allows water to enter can result in fungal growth, wood decay, and structural damage that can end up requiring costly repairs.

Expensive water leaks correlated with windows can often occur between the window units and their frames, but the most predominant leakage paths appear to be based on poor construction and installation techniques of the window and wall interfaces. Water infiltrating through these paths can cause considerable amounts of damage to the wooden framing which often is concealed until the water damage has become widespread. The water management components for windows include the following:

  • Sills and thresholds
  • Water-resistive barriers
  • Flashings
  • Caulking
  • Proper integration with the wall’s water-resistive system
  • Continuous drainage paths

The American Society for Testing and Materials (ASTM) Standard E2112, “Standard Practice for Installation of Exterior Windows, Doors & Skylights”, as well as the International Residential Code (IRC), provide guidance for the performance and construction requirements for exterior windows.  The International Code Council (ICC) provides direction.

“There are two key principles for effective flashing at windows and doors to allow water to drain down the face of the wall and away from the building:

  • Integrate flashing with the water-resistive barrier (WRB), e.g., house wrap.
  • Install membranes shingle-fashion where the top layer of the WRB or flashing laps over the bottom layer to prevent water draining behind the bottom layer”.

One often overlooked component of window installation is the slope of the windowsill. Windowsills that lack a positive slope away are common in the field and contribute greatly to potential water intrusion, particularly when sill pan flashing is omitted in the sub-sill portion of the wall below the window units. Windowsills that are nearly horizontal or, worse yet, slope back toward the interior of the building, create relatively large edges that can collect water and can expedite deterioration of sealants and lead to water intrusion.

A good construction practice is to have a pronounced slope that aids in prompt drainage of water, thus deflecting it away from susceptible sill interfaces. The Brick Industry Association recommends a slope of 15 degrees away from exterior windows for brick veneer applications. This can be achieved by proper planning with the brick mason and determining the height to the window opening.

Replacement Window Flashing

Image Credit: JLC Online, Replacement Window Flashing  https://www.jlconline.com

Another important tool to prevent water intrusion is the use of a water-resistive barrier (WRB). This is critical in the areas around the window opening, which creates interruptions in the drainage plane. Careful attention should be paid to the details for window openings during the design and installation of the water resistive elements around them to ensure proper water management in these areas. Vital points to remember for the installation of WRB is the preparation of the opening with house wrap, felt, or building paper, and the integration with the sill, jamb, and head flashings in order to maintain a continuous drainage plane. As such, there is prescriptive information in the ASTM E2112 document.

Image Credit: Brick Industry Association, Water Penetration Resistance-Design   https://www.gobrick.com

The sub-sill framing below the window opening is another area that is susceptible to water leaks. This typically occurs at the lower corners of the rough opening in the wall, usually where the coverage of the water resistive barrier is minimal. As such, the pan or sill flashing serves to protect the sub-sill framing of the wall and interior portions of a residence beneath the window openings that are susceptible to leakage. Consequently, the sub-sill drainage provided by pan or sill flashing is crucial in achieving the performance and longevity of installed windows. Lastly, the jamb and head flashings will provide reinforcement to prevent water intrusion.

So, you may ask, “How can I find water leaks in my residence without an invasive approach?”  A non-destructive method to identify water leaks in windows is by thermal imaging. Thermal imaging is an essential tool for detecting moisture intrusion. During an investigation, the infrared technology can quickly and non-invasively zero in on the area of concern to find anomalies that may be created by moisture cooling. Monitoring the weather is crucial for successful results. Consequently, it is imperative to choose the optimum time to test and maintain a proper temperature control.  For example, the greater the span in temperature from the outside to the inside of the residence, the better the thermal results. As such, a warm or hot climate is excellent for thermal inspections since air conditioning is cooling the interior of a residence.  The following image depicts an example of this technique.

As can be seen in the above image, the blue areas below the windowsill illustrate an example of a concealed water leak behind the gypsum wall board. It should be noted that the thermal images can reveal a growing problem that can lead to more extensive water damage to a residence.

This residence had substantial water leaks coming through the windows, consequently developing extensive wood decay around the perimeter of the window frame.  Due to the ability to remain undetected, hidden water leaks can grow to become large losses. Using non-destructive tools, such as the Fluke thermal imaging camera, the source of the leak can be identified without unnecessary destruction of property. Getting to the source of the problem as soon as possible is key to avoiding potentially extensive repair work.

Carlos Zarraga has more than 8 years of engineering experience in the structural field specializing in building design, building components and foundation design.  Carlos has designed and analyzed structures, supervised designers and drafters, prepared construction documents and provided on-site duties for field supervision and inspection of construction projects. Certified in RISA 3D, RISA Foundation and RISA Connection, he is well-versed in the analysis of foundation failures.   He often determines the root cause of failure and the resulting scope of damage.  He has designed retrofits to existing structures in addition to repairing construction defects.  He also has experience in the industrial and petrochemical industry designing structures for materials handling facilities and industrial buildings.  Carlos holds a Bachelor of Science in Civil Engineering from the University of New Orleans.

Ammonia – The Good, The Bad, The Smelly… Part One

Ammonia is a compound consisting of one nitrogen atom and three hydrogen atoms and is denoted by the formula NH3. It is often depicted  like this:

Ammonia Atom

Its boiling point is -28°F at atmospheric pressure, so unless it is under pressure, it is gaseous at room temperatures. Therefore, pure ammonia is typically stored under pressure in a liquid form. Household ammonia is only 5-10% NH3, the remaining 90-95% is water. Ammonia is extremely soluble in water.  In fact, ammonia’s affinity for water is so high, that industrial vent streams which might contain ammonia are often bubbled through vessels containing water, and the ammonia in the gas stream will safely dissolve into the water.

Why is this?  The nitrogen atom is highly electronegative.  It draws the electrons from the hydrogen atom to itself.  Therefore, there is a slightly negative charge around the N and a slightly positive charge around the three H’s. This makes it a polar molecule. Water is also a polar molecule, with a negative charge around the O and a positive charge around its two H’s.  Just like magnets, opposite charges attract each other.  The H’s trying to get as close to either an O or an N as the molecules will allow. These are known as hydrogen bonds.  Since these are both water and ammonia are small molecules, they can get pretty close to each other and form relatively strong hydrogen bonds.

Ammonia and Water

Fun fact: water is much more strongly polar (oxygen is a stronger electronegative atom) than ammonia.  This is why their boiling points are so different ( -28° for NH3 and 212°F for H2O).  It takes that much more energy to break the hydrogen bonds of water…..  Now you know!

Ammonia used in industry has had all the water removed from it and is called anhydrous ammonia.  It is both toxic and flammable; its flammability concentration range is 15 – 28%. Ammonia has a strong distinctive odor that is easily detected by most people in concentrations as low as 20 parts per million (ppm).  This is a good thing because the lethal concentration is 300 ppm, so any leaks, although dangerous, are usually detectable before becoming lethal.

Since the hazards of dealing with anhydrous ammonia are so serious, there are many references and guidelines available to lay out how to safely deal with it:

  • The first place to look would be for any manufacturer’s Safety Data Sheet (SDS). Every SDS has sixteen sections which describe the compound’s physical characteristics, important reactivity considerations, etc.  For example, anhydrous ammonia cannot be used with non-ferrous (e.g. copper) or galvanized metals
  • The Occupational Safety and Health Administration created a standard just for anhydrous ammonia: OSHA 1910.11 – Storage and handling of anhydrous ammonia.  It covers a multitude of aspects from storage vessel labeling to piping & pumping requirements
  • The Environmental Protection Agency (EPA) has published the Accident Prevention And Response Manual For Anhydrous Ammonia Refrigeration System Operators, the title of which is pretty self-explanatory
  • International Institute of Ammonia Refrigeration (IIAR) bulletins
  • National Institute of Occupational Safety and Health (NIOSH) bulletins

In Part Two of this blog series, we’ll look at some of the major industrial uses for ammonia….

As President of The Warren Group, Jennifer Morningstar, PE, CFEI, has over 20 years of engineering experience. Her areas of emphasis include chemical release & exposure, OSHA compliance, boiler systems, industrial accident investigation, fires & explosions, product liability and scope of damage/cost to repair analyses. She spent 16 years working at a polyethylene terephthalate (PET) manufacturer.  She is an OSHA-trained Process Hazard Analysis study leader and completed Root Cause Failure Analysis training to become an Incident Investigator. Jennifer authored procedures for lockout/tagout and confined space entry. She has experience as an energy management consultant in a variety of industries including mineral extraction, pulp & paper, animal harvesting & packaging (including rendering) and grain milling.  Jennifer holds a Bachelor of Science Degree in Chemical Engineering from Virginia Polytechnic Institute and State University as well as a Master of Business Administration from the University of South Carolina.

The CE Mark and What Should It Mean to You? Part One

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Two little letters, CE.   Perhaps you have seen those two letters on a machine nameplate or some other equipment.  What is the meaning behind those two stylized letters and how does it drive the design of safer machinery?   Let’s take a closer look. Read More

Shedding Some Light on Fluorescent Light Fixture Fires

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Lighting systems in buildings and other structures have undergone changes over the years.  Many of these changes have occurred as manufacturers have developed more efficient lighting methods.  Lighting loads can represent the largest category of electrical load in many buildings, thus improved lighting efficiency may significantly lower your power bill and can lengthen time between lamp changes. Read More

Collision Reconstruction – Time Distance

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A common car crash is when one vehicle makes a turn or pulls out in front of another vehicle. Normally, without the accident, the vehicles only cross paths for milliseconds. When the collision occurs it’s no doubt because both vehicles try to occupy the same space at the same moment. The question is often “who is at fault?”. Read More

Structure Fires in Eating and Drinking Establishments

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Eating and drinking establishments see an average of 7,410 structure fires per year based on a 2017 report published by the National Fire Protection Association (NFPA). The report analyzed available data from the U.S. Fire Administration’s National Fire Incident Reporting System (NFIRS) and the NFPA’s annual fire department survey for the years 2010-2014.

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Crane Incident Handbook

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Cranes are powerful lifting devices that we see everyday in construction areas, shipping terminals, and industrial sites. They are so common that we often pass by them with little thought. Cranes, however, can easily become involved in incidents that injure people or damage equipment. Read More

Why Visit the Collision Scene?

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If you are a collision investigator, a visit to the collision scene is something you want to do. No matter how much time has passed since the crash compared to the review of the case, the information that can be gleaned from walking through the area is valuable. We aren’t always given the option, but it is very beneficial, here is why. Read More

Hidden Heat: The Unseen Hazard of a High Resistance Connection

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A typical residence can have upwards of 10,000 feet of electrical conductors installed, most of which are buried in the walls, attics and crawlspaces.  A commercial building can have 100,000 to upwards of 1 million feet of electrical conductors.  At each device such as a switch or a receptacle are at least three, and typically six or more connections of these conductors within a junction box.  The connections can be in the form of twisted connectors, screw terminals, push in terminals and crimped connectors.

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Failure to Maintain Tow Hook Latch Results in Bystander Death

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An unfortunate and tragic case that we investigated involved a commercial “rollback” recovery truck that was being used to transport a four-wheel drive diesel pickup.  The diesel pickup was not in running order with its’ engine in the bed of the truck.  Consequently, a commercial towing company was hired by the truck owner to transport the truck.  In the process of loading the truck onto the rollback, the truck came uncoupled from the winch and cable system.  The truck then rolled down the inclined bed of the rollback, running over and killing a bystander. Read More

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