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Protecting a building's interior from the elements is a critical design challenge for any construction project. In most cases, a multi-faceted solution is necessary to prevent damage from environmental risks such as moisture penetration, air infiltration and temperature fluctuations. The quality of a building envelope's flashing—a weather-resistant seal situated at joints—is one critical consideration that substantially impacts a building's weather resistance. Unfortunately, many traditional flashing solutions are costly at best and ineffective at worst, requiring builders to spend excessive amounts on additional labor and materials to achieve a satisfactory seal.

SillDry is an innovative zero-waste, injection molded flashing solution designed to mitigate these problems. Compared to traditional flashing, SillDry is cheaper and easier to install, while still offering enhanced insulation and drainage performance.

What is the Building Envelope?

A building envelope is comprised of the components that isolate the building from the external environment. This includes the:

  • Foundation
  • Walls
  • Roofing system
  • Windows
  • Doors

The building envelope provides structural integrity and a protective barrier against moisture, temperature, and air flow changes. 


For the building envelope to function effectively, each component must contend with unique environmental factors. The roof of an enclosure, for instance, is most vulnerable to wind, precipitation, and temperature fluctuations, whereas the foundation must defend against its wet earthen surroundings. Depending on their placement, windows, doors and walls may face all of these pressures to various degrees, though windows and doors are often especially vulnerable.

A sturdy building envelope must achieve several goals simultaneously if it is to protect the structure. It’s important to insulate the building against temperature fluctuations and seal out precipitation and humidity. Preventing all water from entering a structure is virtually impossible; so the building envelope should also have a mechanism to capture or divert water at vulnerable points. High-quality flashing is one of the best ways to deal with inevitable water flow while also sealing the building against other risks.

Why Do Building Envelopes Matter?

Building envelopes are the most important line of defense against moisture, thermal fluctuations, and unwanted airflow. The building envelope prevents problems ranging in severity from drafts to complete structural failure. In terms of both comfort and structural integrity, the building envelope drives the end user experience.

Another reason to attend to the building envelope is its role in energy performance. Consumers and building codes both demand efficient power consumption, which is unattainable without a tightly insulated building. With a weak building envelope, heating and cooling quickly become costly and unsustainable—problems that can be mitigated with proper flashing and envelope design.

Options For Sealing Building Envelope

Many of the common sealing solutions have significant downsides, despite their widespread use. Sealing a structure poorly is only a stopgap for failures down the line.  “A penny of prevention is worth a pound of cure” (Ben Franklin) so it's better to carefully consider sealing options from the beginning of any building project.

Adhesive Tapes

Adhesive tapes are one of the most common sealing mechanisms for windows, doors, and roofing components. Tapes are typically chosen for their simplicity and versatility, but they are not an ideal solution on their own. Flashing tape requires labor-intensive expert installation as well as good weather while generating substantial amounts of waste.

Over the long-term, flashing tape is more vulnerable to failure when exposed to UV rays and/or extreme temperatures, minimizing the benefits seen early on. In addition, by themselves, tapes do not meet the building code requirements as they do not have any positive slope to drain the water that collects underneath the window or door.  If adhesive tapes are used, they should be part of a well-rounded insulation strategy that includes more durable fail-safes.

Metal Sill Pans

Sill pans are required at exterior doorways and certain vulnerable windows to divert standing water. While sill pans serve an essential function in moisture control, traditional metal pans come with some significant disadvantages. Not only are they expensive, but their metal construction is also inflexible, which can lead to cracking with temperature fluctuations. A vulnerable window sill leaves the structure itself at risk from the water damage it was meant to protect against.

SillDry Sill Flashing System

SillDry's sill flashing system is not a simple “pan”.  SillDry is made from injection-molded thermoplastic olefin (TPO) to eliminate the drawbacks of traditional metal pans. The benefits of the Sill Pan include:

  • Durability. TPO is known for its resistance to common environmental hazards, meaning that SillDry pans won't crack like metal when the temperature dips too quickly. Compared to metal models, SillDry's product is incredibly durable, resisting damage from impacts, UV exposure, extreme temperatures, and moisture. TPO also resists degradation from dirt and bacteria, making it a superior choice for sills that are frequently exposed to these risks and other harsh conditions.
  • Innovative design. SillDry’s innovative design offers an optimal balance of adaptability and superior performance. The SillDry sills are pre-sloped with precision-engineered drainage channels for water management.
  • Easy installation. SillDry also boasts patented Accordion-Fit technology which allows each sill to seamlessly expand for installation. SillDry securely fits all standard sill sizes from 18” inches to 12’, bringing its revolutionary protection to virtually any building project. Where traditional methods require prolonged skilled labor for installation, SillDry installs in a manner of seconds, making it the most cost-effective way to comply with building codes.  
  • Affordability. All of these benefits come with significant cost savings over metal pans or tapes. Further cost savings come in the form of increased longevity, reduced maintenance, reduced call-backs, and avoiding costly repairs to waterlogged structures.

We're so confident in SillDry's performance that we offer a 15-year warranty to guarantee its performance. 

Learn More About SillDry's Flashing Solutions


Architects, engineers, and contractors can't afford to stick with wasteful or ineffective protective measures to protect the building envelope simply because they are the “way we’ve always done it.” SillDry was designed by visionary construction experts looking for a better water management solution, and they found it in SillDry's precision-engineered, American made, thermoplastic design.

We've drawn on our extensive industry experience to put together this e-book discussing best practices in building envelope design, including flashing options and other critical considerations. Download the eBook to learn more about how SillDry would fit into your project, contact our team or request a quote today.