The Cavity Wall Conundrum

Complex, modern building designs require balancing the need to keep the building dry, airtight, thermally efficient, and code compliant. Photo © Vladimir Sazonov Shutterstock.com

A new e-book called the “Evolution of Building Enclosures”, published by Construction Specifier, offers a four-part series, including an article on what the magazine calls “the cavity wall conundrum”. Authored by Todd Skopic, a building science manager, the article provides an in-depth, technical look at the use of open-joint rain screens coupled with unconventional wall orientations. While these configurations can be appealing, they also pose a potentially dangerous combination; abating water ingress is an important issue to address, but these systems must be compliant with building codes, including those that test for combustibility.

Balancing the need to keep the building dry, airtight, thermally efficient, and code compliant can create what Skopic calls a cavity wall conundrum. As more architectural firms push the limits of building design, ensuring a safe and efficient building envelope is becoming more complex. The growing practice of combining open-joint rain screens with unconventional wall orientations, such as a backward-sloping configuration, offers a prime example.

In such structures, design teams want to prevent water ingress, but they also need to follow the latest building codes. Staying compliant with certain ones, such as the energy code, complicates matters by introducing certain materials that increase potential safety risks.

Managing water with building enclosures involves the three Ds: deflection, drainage, and drying. Open-joint rain screen systems offer an increasingly popular means to achieve the three Ds and behind every open-joint rain screen, is an air and moisture barrier to defend against water ingress. All of these solutions are subject to and must comply with an abundance of codes and regulations.

The 2012 International Building Code (IBC) requires buildings in Climate Zones 4 to 7 to have a continuous air barrier, which in most cases also takes the form of a water-resistive barrier. The 2012 International Energy Conservation Code (IECC), is also driving the use of continuous insulation (ci), which in some cases is combustible. It needs to comply with the National Fire Protection Association (NFPA) 285 – a standard fire-test method for evaluating the fire propagation characteristics of exterior, non-loadbearing wall assemblies containing combustible components.

In other words, today’s design teams are trying to design building envelopes that are watertight, airtight, thermally efficient to meet code requirements, and to be NFPA 285-compliant. Solving this ‘cavity wall conundrum’ is possible, but it requires some familiarity with the competing design challenges and different industry standards.

This in-depth, technical article discusses rain screen design, and the standards for managing air and water, in context of the codes for continuous insulation (ci), air barriers, and water-resistive barriers, as well as life safety issues related to combustibility. For instance, how do cladding attachments impact a system? What is the the value of a continuous insulation system with adhesive-backed sheet membrane that isn’t penetrated? What are the differences between sprayed polyurethane foam (SPF) and expanded polystyrene (EPS) when used as insulation in cavity wall assemblies, vis a vis thermoplastic extruded polystyrene (XPS) which is a thermoplastic foam rigid insulation board? And how do these compare with mineral wool or fire-enhanced polyisocyanurate (polyiso) mineral wool in performance and code compliance? And what are all the codes?

Solving the Conundrum

Building designers are increasingly aware of the competing requirements and standards involved in modern cavity wall design. They should know continuous air barriers and insulation systems, along with NFPA 285 code and other compliance issues, which must be balanced with the goal of keeping water out of a building. Achieving this balance will help designers create the safest, most effective building envelope possible and thus solve the cavity wall conundrum. And on the building materials front, manufacturers need to test all their products to ensure they meet the extensive industry standards and testing.

The other chapters in the new e-book cover the benefits of specifying complete masonry veneer wall systems, defining and testing construction tape and flashing durability, and moisture in new concrete roof decks.


Sto Introduces New Air Barrier & Waterproofing Product — RapidGuard

Sto has introduced a new, state-of-the art air barrier and waterproofing material.

Now you can stay ahead of fast-paced construction schedules with a new easy-to-use air and moisture barrier product from Sto. Sto RapidGuard™ is a single-component, multi-use air barrier and waterproofing material that seals rough openings, seams, sheathing joints, cracks, penetrations, and transitions in above-grade wall construction.  Introduced this week; it is now available in the US and Canada.

“The material is fast-drying, and its flexible coverage makes it easy to provide high-quality air and moisture control across multiple applications,” said Karine Galla, Product Manager for Sto Corp.  “It gets the job done quickly and enables applicators to finish their work despite potentially adverse weather conditions.”

RapidGuard works seamlessly with Sto waterproof air barrier membranes, including Sto Gold Coat® Sto EmeraldCoat® Sto AirSeal® and StoGuard VaporSeal®

Costly shutdowns due to rain can be avoided because Sto RapidGuard adheres to damp substrates without blistering or increasing drying time. The product can even be installed in near-freezing temperatures.

The innovative new product has excellent elongation, allowing it to bridge cracks and seams in wall construction without tearing or compromising the established air and moisture barrier.  It works seamlessly with Sto waterproofing air barrier membranes, and is compatible with concrete, concrete masonry, brick, gypsum sheathing, wood, galvanized material, and cement-based sheathings. Because it is a single-component product, there is no need for tape, mesh or fabric; it can be easily applied without the use of special tools or applicator training.


AWCI Celebrates 100 Years with Centennial Book

AWCI has published a history of the wall & ceiling industry in a new book celebrating the organization's Centennial anniversary.

In March, the AWCI (Association of the Wall & Ceiling Industry) celebrated its 100th Anniversary in at its annual convention and INTEX Construction Expo in Orlando, Florida. Part of the celebration was to mark the publication of a new book to commemorate the organization’s birth in 1918; the special edition Centennial Book provides an historical overview of the wall and ceiling industry during the past 100 years.

The handsome, large-format book documents a century of industry growth with a decade-by-decade synopsis of the wall and ceiling industry, with many vintage and contemporary photographs that also tell the story.  As illustrated in the new book, wall and ceiling construction has always been a basic service; it survived the ravages of a turbulent century, continues to innovate and remains a robust industry today.

Sto Corp. was the proud sponsor of the 1920’s section of the Centennial Book; a memorable decade that started with the introduction of Prohibition and ended with the stock market crash in 1929, with flappers, Lindbergh’s pioneering trans-Atlantic flight, and the migration of Americans from farms to cities providing memorable milestones. On the wall and ceiling front, Gold Bond gypsum wallboard was introduced, and the labor movement grew in strength. The American Federation of Labor (AFL) had 5 million union members in 1920; higher pay and shorter workdays were contested issues, and skilled tradesmen were in short supply. (Sound familiar?) In 1926, 2,500 Chicago journeymen plasterers went on strike demanding a $2/day wage increase. Overall, each decade in the book provides many insights in the development of the wall and ceiling design and construction business.

As told in this industry memoir, the AWCI has taken a leading role in setting standards since its inception, facilitating union agreements, protecting and promoting the trade. As a forum for unity and direction, the AWCI has helped transform the industry into what it is today and should be applauded for its industry leadership and support for superior building standards over the past 100 years.


High Performance Insulated Wall System a Game Changer for Architects

High performance insulated wall systems like the innovative StoTherm® ci XPS provide the air, weather and thermal tightness required for today’s most energy-efficient architecture, but are also cost-effective and provide designers with a wide range of aesthetic options.

Sto Corp. has joined forces with insulation specialists Owens Corning and Dow to produce one of the most technically advanced exterior wall systems available. The innovative StoTherm® ci XPS wall system is designed to provide the air, weather and thermal tightness required for today’s most energy-efficient architecture, but also makes for exterior walls that look good, and are cost-effective.

One of the first things architects will notice about the product is its design flexibility. The multi-layered system offers a wide range of finishes from the natural look of raw materials to boldly colored finishes, allowing for a variety of looks from traditional textured surfaces to limestone, concrete, metal and many more.

Hidden behind the beautiful outer skin, are important energy efficient properties; StoTherm® ci XPS meets rigorous sustainable design standards, including ASHRAE 90.1-2010, the new International Green Construction Code (IGCC), and the International Energy Conservation Code (IECC) requirements for continuous insulation.

This smart architectural product combines high quality, technologically advanced materials, including Dow and Owens Corning insulation with a closed cell structure which helps prevent liquid movement through the material and provides exceptional thermal performance with an R-value of 5.0 per 1”. The final result is a combination of layers that delivers exceptional air and moisture control, that also meets the latest building code requirements for energy efficient continuous insulation and fire testing. The highly durable system also provides significant impact resistance that exceeds IBC and IECC codes.

How can such a high-performance product, also be economical? The high R-value of Sto’s system (R5/inch) makes for a thinner wall, reducing the overall weight and cost-per-square foot for the building envelope. Add this to lifetime savings from superior energy-efficiency, and you have a product that offers both short- and long-term cost benefits to the client.

StoTherm® ci XPS is truly a system designed with the architect in mind –its versatile and seamless combination of energy-efficient qualities and aesthetically pleasing finishes provide a true “end-to-end” solution for architects.

 


Material Selection Conference Yields Valuable Product Data

Sto product experts participated in Durability & Design’s Material Selection Conference last week which showcased the latest in high performance coatings and air moisture barrier products for exterior walls.

At Durability + Design’s inaugural Material Selection Conference last week (Sept. 26), the themes that prevailed were data collection and communication. Though different challenges were discussed — from air leakage to moisture damage — the resounding message was: know your materials inside and out.

The one-day forum focused on the capability of coatings to manage moisture intrusion into exterior walls, and how liquid-applied air barriers can limit heat, air and moisture transfer through walls. The effect of permeance on exterior wall coating performance, as well as how specific coatings and water repellent brands performed on exterior walls were also discussed.

Manufacturer representatives participating in panel discussions offered their opinions on a variety of scenarios and recommended applicable products. Chuck Duffin, Ed Telson, and Tyson Lodge, representing Sto Corp., participated in these panels, educating attendees on how Sto coatings and air moisture barrier products perform on exterior walls in different conditions and circumstances.

Andre O. Desjarlais, program manager for the Building Envelope Systems Research Group at Oak Ridge National Laboratory, discussed the importance of WUFI software (an acronym for Wärme Und Feuchte Instationär—which, translated, means heat and moisture transiency) and why this hygrothermal modeling is valuable based on the wide range of materials available today consistent with the drive for energy efficiency.

While WUFI models yield a lot of data for designers of durable building envelopes, understanding this data and using it appropriately are critical for achieving the construction of energy-efficient, moisture-resistant walls, roofs and basements. Again, the need for knowing your products and how to apply them was reiterated.

The value of using the web-based Energy Savings Calculator developed by ORNL, along with quality assurance and installation requirements for liquid-applied air barriers, were also discussed to ensure building envelope energy efficiency and air tightness. It was noted that air leakage rates of a building depend on multiple variables, including envelope airtightness, HVAC system operation, occupancy, weather and the stack effect. Fluid-applied air barrier products and installation considerations were also debated.

The overall objective of the event was about making buildings last longer by integrating design objectives with exterior performance objectives, selecting materials wisely and knowing those materials. Regardless of which products are selected for durability and design, the manufacturers, architects and contractors in the audience seemed to agree that working closely with, and consulting, manufacturers regarding air barrier and wall coating products was the best way to ensure successful project outcomes.

 

 


Designing for Resilience—Part Two

Sto Therm ci is an exterior insulated wall system that can stand up to blows and abuse; it can be as durable and impact-resistant as you want to make it.

Having provided a macro look at design issues based on increasingly dramatic and devastating weather events, this week we are going to look at specific resilient design solutions and products as they relate to wind and water, specifically Hurricane Impact (HI) systems.

Hurricane impact resilient design can save lives, structures and money. Hurricanes inflict costly damage on the populated areas where they hit, causing billions in insurance losses, costly business disruptions, and taxpayer dollars spent on disaster management. With more than 50% of the American population (who account for 58% of the nation’s gross national product) living or working in coastal counties; these hurricane-prone areas call for well-sealed buildings that also allow for adequate drainage. Severe wind load, heavy precipitation and ground level flooding all need to be addressed.

Creating smarter exteriors for storm protection

Stricter building codes have contributed to improved resilient design, but so have innovative building products and systems. Exterior insulation finish systems (EIFS) and air moisture barrier (AMB) products have been available for decades, and have always been a “resilient design” solution, but they weren’t necessarily referred to as such.

Using specialized EIFS, AMBs and other exterior wall products and systems to enhance design resiliency can provide protection from some of the most severe weather conditions in North America involving high-wind events and moisture intrusion.  Hurricane protection systems for exterior walls can be economically installed on a variety of substrates including metal frames with gypsum sheathing, wood or steel frames with plywood sheathing or concrete masonry. Many of these are also available in a wide range of decorative and protective wall finishes so that form doesn’t have to be sacrificed to function.

As EIFS have evolved, so has the market for advanced solutions for exterior cladding options that protect against hurricane and tropical storm winds, water intrusion and windborne debris (missile impact).  Exterior walls may be susceptible to damage and can result in building envelope failures in such storms. In most cases, windows will fail before the exterior wall, so one of the key components of good resilient design is an air/moisture barrier with connections and transitions that integrate the window and penetration points, creating a monolithic barrier across the entire building. Specialty systems for coastal construction, incorporating innovative wall systems can offer more wind-and-water-related structural protection.

One of those protective products is Sto Corp’s StoTherm® ci exterior insulated wall system, which can stand up to the full range of blows and abuse that Mother Nature can dish out. You can make it as durable and impact resistant as you want by simply swapping out the standard basecoat and mesh and substituting more flexible or resilient components . The product meets the ultra-high impact class per ASTM E 2486 at 150 inch-lbs. Just how tough it is, can be appreciated here: https://youtu.be/LkEFv7O3s_cArchitects, engineers and builders, as well as politicians and city planners need to understand and take advantage of products that can be incorporated into design strategies to protect valuable buildigs that are subject to severe wind and water intrusion.

Advanced resilient design solutions can offer structural protection and enhance public safety, but also deliver significant economic benefits