Forensic Engineers and Consultants

Tag Archive: Warren Forensics

  1. Issues with Moisture Intrusion through Flashing into Wood-Framed Structures

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    Flashing is a hot-button topic amongst residential designers, builders, and claims adjusters alike. In fact, currently one of the most prominent construction defect claims that we see involves moisture intrusion around improperly flashed window openings in wood-framed structures. Other trouble spots include the roof penetrations at chimneys and vent pipes.

    The design intent of flashing is to allow moisture to move out, down, and away from a structure. Water will remain on the outside of a building where it belongs if the right methods and materials are used.  Water is a shrewd opponent. It can be driven by wind or sucked into crevices by negative air pressure inside the structure, after which it can actually flow uphill between construction layers. Once inside, water will subject building materials to alternating spells of soaking and drying. until decay of the wood framing members finally results.

    We all know that if there are any ways for water to get in, it will find those entry points. Unfortunately, if water seeps in around a window, chimney, or vent pipe, the damage it can do to the wooden structural components such as plywood sheathing, wall studs, floor joists, and roof rafters usually occurs before the leak is detected. This is the case because these components are hidden by their coverings and finishes. Therefore, often the damage is done before it becomes too late to avoid invasive, destructive, and costly repairs.

    Image Credit: Doityourself.com

    First, I will examine flashing around window openings. Most modern windows are made of wood, have metal nailing flanges around their perimeter, and are clad with either aluminum or vinyl on their exterior to protect the wood from the weather. Flashing typically consists of bituminous tape, i.e., bituthane, applied at the head, sill, and jambs of the window. How the housewrap moisture-resistive barrier (MRP) interfaces with this flashing is of primary importance. When the cut edge or “flap” of the housewrap is run behind the tops of the windows, as shown in the picture below, the opening cannot be flashed properly. The housewrap top flap should be pulled up on the exterior of the building at the top of the window, the corners taped, and the flashing applied over it. As always, the specific window manufacturer’s written instructions for flashing should always take precedent. When brick masonry veneer cladding is used, additional “thru-wall” flashing through the brickwork is required to ensure that the structure is properly sealed against any moisture which may end up behind the brickwork.

    Window building wrap. Image credit: Instructables.com

    Improperly flashed chimney using EPDM rubber. Photo Credit: www.exteriorproinc.com

    Improperly flashed chimney with missing shingles. Photo Credit: www.exteriorproinc.com

    Next, I will look at the installation of flashing around roof penetrations at chimneys. This flashing is typically made of metal, such as copper, aluminum, or galvanized steel. EPDM rubber may also be used.  The goal is to achieve a leakproof chimney penetration assembly. Roofers are usually responsible for flashing chimneys, but this can be one of the toughest tasks of a roofing job, and requires the most experience and skill. Because of this, on many re-roofing projects, the roofers may even skip the installation of new flashing altogether and rely on the old, original flashing to keep the new roof dry. As one can imagine, this seldom works out well for the homeowner. The pictures below is are examples of botched chimney flashing jobs, which not only have the appearance of shoddy workmanship, but probably leak as well.

    Finally, I will examine a method for installing flashing around roof vent pipe penetrations. This flashing is available in premolded or prefabricated “boots”, which are properly sized for the specific vent pipe, and fit snugly over the pipe. The boot is set down onto a bed of fresh roofing cement/caulk. Then, the shingles are installed, with one shingle notched to fit around the flashing boot, as shown in the graphic below.  This method is very basic and straightforward, and when done correctly, will ensure a leakproof assembly.

    Remember: The goal is a perfectly dry structure. Properly installed flashing can completely weatherproof a home and make it impervious to stormwater and condensation, which can cause major problems if they find their way to the wrong places. If you have a water intrusion claim, always investigate possible issues with flashing.

    George Sanford, PE, holds a Bachelor of Science in Mechanical Engineering from North Carolina State University in Raleigh, North Carolina. George has more than 20 years of applied structural engineering experience specializing in residential, commercial, and industrial structures and foundations. Throughout his career, George has designed and analyzed structures, supervised engineers, prepared construction documents (drawings and specifications).  He has an in-depth knowledge of many building codes, standards, rules, and regulations including the agencies that govern and provide guidance to building designers such as the International Code Council (ICC) American Society of Civil Engineers (ASCE), Steel Joist Institute (SJI) and the American Iron and Steel Institute (AISI).

  2. Industrial Equipment Failures and Construction Disputes

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    At Warren, we frequently investigate losses involving industrial machinery.  Many of the losses involve workplace injuries, fires, or explosions; however, we also analyze industrial machinery and processes for other types of problems.  For example, we analyze failures of machinery or industrial processes to perform as expected or disputes that arise from the commercial supply and construction of such systems.  This can encompass a range of issues from failure to achieve required levels of product quality or production quantity, to matters concerning unclear specifications or contracts, (more…)

  3. Heavy Machinery Fires Caused by Hydraulic Hose Failures

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    Heavy machinery fires are often caused by hydraulic hose failures.  Pressurized hydraulic fluid escaping from a failed hose assembly can be atomized into a fine spray that can be ignited by heated engine surfaces such as the engine exhaust or turbocharger.

    Hydraulic hoses near the engine compartment of an excavator that burned.

     

    Hydraulic hoses often fail due to age and wear, requiring regular inspection and replacement of hydraulic hoses to prevent failures. Hoses may also fail if they are misrouted.  Misrouting can lead to the hose being pinched or causing it to chafe against a sharp metal surface. (more…)

  4. Installation of Structural Sheathing on Wood-Framed Structures

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    The facts presented in this blog lead to an interesting story.  During the heyday of the residential construction boom in coastal South Carolina circa 2005, many General Contractors were forced to go out-of-state to find framers and other subcontractors due to the demand creating a local labor shortage.  It turned out that the state of Texas had excess capacity and availability of framers and carpenters. Many Texas framing crews came to South Carolina to satisfy the shortage.  It soon became apparent that the Texas crews, many of which were from inland locations, were accustomed to installing 4’x8’ exterior wall sheathing with the long dimension vertical, i.e., parallel to the studs.  It is especially important and required that the long dimension be oriented perpendicular to the studs.  Laboratory testing has shown that (more…)

  5. Types of and Techniques for Reinforced Concrete Masonry Block Construction

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    Construction using concrete masonry blocks or units (CMU) is ubiquitous in the United States today, and in fact in the whole modern world.  CMU blockwork is a very versatile and relatively economical building material.  It is naturally strong in compression, but with reinforced, grout-filled cells, it can also withstand large shear, bending, and tensile loads imparted by lateral wind or seismic events.  In this article, I will discuss the various types of CMU designs, as well as terminology, construction techniques, and application uses.

    The design of CMU is typically comprised of hollow concrete “face shells” with (more…)

  6. Uplift and Shear Restraint Techniques for Residential Structures in Hurricane Wind Zones

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    Hurricane and Tropical Storm strength wind forces can wreak havoc on wood-framed residential structures.  One of the primary hazards is the negative pressures which can develop on the exterior building envelope when the structure is subjected to the high encircling winds.  These negative pressures act like the suction of a giant vacuum on a dwelling’s roof diaphragm, which produces enormous uplift forces throughout the entire structure.  The leeward walls are also subjected to negative pressures, while the windward walls take the brunt of the positive wind pressures.  The uplift on the roof is caused by what the author dubs “the airplane wing effect”.  In other words, (more…)

  7. Interpreting Industrial Incident Data – Lesson Learned

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    This is a case study about an incident I investigated involving a major upset in a distillation column.  This blog builds on the previous blogs about the Distributed Control System, DCS – Data is the Key.

    Distillation is a method of separating mixtures of compounds with differing boiling points.  Uncle Bill with his still on the hill separates ethanol, that boils at 173°F, from water that boils at 212°F.  If the mixture is heated to above 173°F, but below 212°F, the ethanol will boil, the vapor will travel up out of the unit and then can be condensed and served over ice with an olive…   Any mixture of two or more chemicals with different boiling points can be separated in this way.  The distillation (more…)

  8. TVSS or SPD … Can I Buy a Vowel? Understanding Surge Protection and the Changing Requirements

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    Surge Protective Devices (SPD), formerly known as Transient Voltage Surge Suppressors (TVSS) have been around for a long time.   The most recognized version is integrated into outlet strips and used to protect sensitive electronics from surges, or higher than expected voltages on the power line.  Early versions of these surge strips were known to have problems where internal components could overheat and cause a fire.  Thermal protection was added to the designs to greatly reduce the potential for a fire hazard.  Such an implementation in an outlet strip is considered a Type 3 SPD. (more…)

  9. The Condensate System – An Important Item in Routine HVAC Maintenance

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    HVAC systems are almost everywhere in the United States now.  As a life-long resident of the humid south that grew up in a home without central air conditioning; I definitely appreciate the ability of a well-designed and maintained HVAC system to remove the oppressive summer humidity.

    The very humidity that makes your clothes damp with sweat and hastened the invention of cooled leather seats in automobiles also has another route to create havoc…condensate.

    In order for an HVAC or “air-conditioning system” to reduce the humidity in the air of your home or office it must first cool the air down to a point where the air can no longer keep the moisture in suspension as water vapor.  The moisture must condense… creating condensate.  This is what is happening when your cool beverage of choice “sweats” on the exterior of the container in the humid summer. Now that you have liquid water, as opposed to water vapor, this condensate must be directed out of your conditioned space to prevent water damage due to backed up or leaking condensate. (more…)

  10. What Does a Recovery Boiler Recover? – Quite a bit, actually!

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    The Kraft paper process was invented in 1879 and produces a stronger finished product that other paper manufacturing methods. One of the waste streams is known as black liquor and is a mixture of solids and water.  It contains lignin, hemicelluloses and chemicals used in the pulping process. The original process had no use for this harmful waste stream and it was dumped into nearby waterways, to their detriment!!!  Mr. G.H. Tomlinson invented the recovery boiler in the early 1930’s.  This development made the Kraft process the manufacturing method of choice, as explained below. (more…)

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