Building Better Walls PART THREE: Vapor Control & Thermal Control

Nike World Headquarters in Oregon where Sto VaporSeal® was used as an air moisture barrier.

Nike World Headquarters in Oregon where Sto VaporSeal® was used as an air moisture barrier.

The fact that many vapor barriers also retard or eliminate airflow sometimes causes confusion about the functions of the ABS and vapor barriers. The function of a vapor barrier is to control  water/vapor diffusion and reduce the occurrence or intensity of condensation. As such, a vapor barrier has one performance requirement: it must have the specified level of vapor permeance and be installed to cover most of the area of an enclosure.

That being said, vapor control systems are either vapor permeable or impermeable membranes. Determining which type you need primarily depends on climate and wall design.

There are a wide range of products and systems available today that employ formulations suitable for any climate. These will protect buildings from water infiltration in high-rainfall regions, as well as from water vapor drive and unwanted air movement. (Example: STO VaporSeal®) Fluid-applied, vapor-permeable building membranes are especially versatile, and may be used under a variety of mechanically attached claddings, including cement board, wood, vinyl, brick, stone and metal panels.

Providing thermal comfort without overspending on excessive space conditioning costs is also one of the primary requirements of today’s building designs.. Therefore, thermal control is an important aspect in almost all buildings. Understanding heat transfer and the temperature distribution through building materials and assemblies is critical for assessing energy use, thermal comfort, thermal movements, durability, and the potential for moisture problems.

The key components for controlling heat flow in building walls requires insulation layers that aren’t penetrated by thermal bridges, an effective air barrier system, good control of solar radiation and management of interior heat generation.

So, in conclusion of our three-part series, a “clever” wall (we’ll even venture to say a “smart” wall), needs resilient design components that control air, moisture, vapor and thermal conditions. Get the wall right and it can make all the difference in creature comfort, energy efficiency and economics. Whether you’re retro-fitting or building from scratch, wall systems that can provide all four key controls are what you want.


Building Better Walls PART TWO: Air Control

The second part of our series on Building Better Walls focuses on air control and the basic requirements for air barriers systems in walls.

The second part of our series on Building Better Walls focuses on air control and the basic requirements for air barriers systems in walls.

The management of airflow is important for several reasons: It controls moisture damage, reduces energy losses, and ensures occupant comfort and health. Airflow through a building enclosure is driven by wind pressure and the stack effect – movement caused by warmer air rising and colder air falling that create pressure differences. These, in turn, can lead to air leakage, unexpected airflows, and indoor air-quality problems. Mechanical air handling equipment such as fans and furnaces also impact air flow.

A continuous, strong, stiff, durable and impermeable air barrier system is required between the exterior and interior conditioned space to control airflow driven by these natural phenomenon. Wall air barriers provide critical protection in all buildings, regardless of region or climate. Controlling air leakage within the building envelope also enhances a structure’s energy efficiency.

Basic Requirements of Air Barrier Systems for Walls

Typically, several different materials, joints and assemblies are combined to provide an uninterrupted plane of primary airflow control. Regardless of how air control is achieved, the following five requirements should be met to achieve a proper air barrier system (ABS):

  1. Continuity.  Enclosures are 3-D systems! Continuity must be ensured through doors, windows, penetrations, around corners, at floor lines, soffits, etc.
  2. Strength.  The ABS must be designed to transfer the full design wind load (e.g., the one-in-30-year gust) to the structural system. Fastenings can be critical, especially for flexible non-adhered membrane systems.
  3. Durability. The ABS should continue to perform for its service life. Ease of repair and replacement, the imposed stresses and material resistance to movement, fatigue, ambient temperature, etc. should all be considered.
  4. Stiffness. The air barrier must reduce or eliminate deflections to control air movement into the enclosure; it must also be stiff enough that deformations do not change the air permeance (e.g., by stretching holes around fasteners) and/or distribute loads through unanticipated load paths.
  5. Impermeability.  Typical recommended air permeability values are less than about 1.3 x 10-6 m3/m2/Pa. In practice, the ability to achieve continuous insulation is more important to performance; the air permeance of joints, cracks, and penetrations outweighs the air permeance of the solid materials that make up most of the ABS. Hence, a component should have an air leakage rate of less than Q< 0.2 lps/m2 @75 Pa, and the whole building system should leak less than Q< 2.0 lps/m2 @75 Pa.

It is important to note that increased airtightness must be matched by an appropriate ventilation system to dilute pollutants, provide fresh air, and control cold weather humidity levels. Good airflow control through and within the building enclosure will bring many benefits including reduced moisture damage, lower maintenance costs, energy savings, and increased health and comfort.


Building Better Walls PART ONE: Moisture Control

The key components to building better exterior walls systems are: sheathing joint treatments, rough opening protection, transition membranes and an effective air/moisture barrier.

The key components to building better exterior walls systems are: sheathing joint treatments, rough opening protection, transition membranes and an effective air/moisture barrier.

The moisture layer in an enclosure assembly controls the passage of water even after extended exposure to any moisture. The water control layer is the continuous layer (comprised of one of several materials and formed into planes to form a three dimensional boundary) that is designed, installed, or acts to form the wall’s rainwater boundary. In face-sealed, perfect barrier systems, this is the outer-most face of the enclosure. In concealed barrier perfect systems, it is a plane concealed behind the exterior face. In drained systems, the water control layer is the drainage plane behind the drainage gap or drainage layer. In storage reservoir systems, the rain penetration control is typically part of the innermost storage mass layer.

Key components for moisture control in wall systems are: sheathing joint treatments, rough opening protection, transition membranes and an effective air/moisture barrier. Pre-formed drainage mats can also help remove water, as well as promote drainage and drying in vertical wall assemblies beneath stucco, stone, siding and thin brick veneers. (Example Sto DrainScreen)

Fluid-applied, waterproof air barrier membranes in wall construction have proven their worth as excellent protection against moisture intrusion and air leakage, delivering thermal value in the form of significant energy savings in hot and cold climates. (Example: StoTherm® ci XPS) These fluid-applied air/moisture and vapor barriers may be used with all types of above-grade claddings and wall substrates. Trowel-applied air/moisture barrier and adhesives may be used for above- and below-grade walls and for attaching continuous insulation.

Look for wall systems that provide seamless air and moisture control as opposed to building- wrap barriers that are typically penetrated by staples and fasteners for attachment. An entire wall assembly that provides seamless protection will provide reliable control layers for air and moisture intrusion.

Wall coatings can also offer protection against moisture and rain, along with UV degradation, heat, salt, wind and humidity. Coatings with permeance can help resist blisters and mold in a wall cavity, which can be caused by moisture resulting from vapor migration.

In addition to repelling external water and moisture, an advanced coating system can also help resist cracking and prevent corrosion in substrates containing steel. While every building is different and coatings will vary based on cladding types and other variables (such as regional climate), wall coating formulations today are not only weatherproof, but can offer vapor permeability, crack-bridging capability, and mold resistance; some are so high-tech they create a durable surface that both beads water and sheds dirt, thus self-cleaning a wall. (Example: StoColor® Lotusan®)

 


Three Part Series on Exterior Walls

The science of exterior walls has been well-documented; look for our three-part series that starts next week.

The science of exterior walls has been well-documented; look for our three-part series that starts next week.

Starting next week, ARCHITRENDS is launching a three-part series on building better walls, thanks to a big assist from the Building Science Corporation (BSC) – a consulting and full-service architecture firm for commercial, institutional and residential buildings. An internationally recognized organization, BSC’s focus is preventing and resolving problems related to building design, construction and operation. Probably best known for their expertise in moisture dynamics, indoor air quality and forensic investigations into building failure, BSC advocates for sustainable design, energy efficiency and environmental responsibility in building technology. Their website www.Buildingscience.com  is a free online resource.

Better Walls for Buildings

The perfect wall is an environmental separator—it must keep the outside out and the inside in.  Therefore, in a world of perfects walls, a wall assembly must control rain, air, vapor and heat. Functional, resilient walls need four principal control layers:

  • moisture control layer
  • air control layer
  • vapor control layer
  • thermal control layer

As BSC points out, if you can’t keep the rain out, don’t waste your time on the air. If you can’t keep the air out, don’t waste your time on the vapor and forget about thermal. The perfect wall includes a water control layer, with an air control layer and vapor control layer positioned directly on the structure, and a thermal control layer covering the other control layers.

Expansion, contraction, corrosion, decay, ultra violet radiation (basically, most bad things!) are all functions of variations in temperature. So, control layers need to go on the outside to help the structure weather temperature extremes and protect it from water in its various forms, as well as ultra violet radiation.

The “clever” wall, as BSC calls it, uses building material that combines all four controls. Thus, air moisture barrier systems (AMBs) and exterior insulation finish systems (EIFS). The most “clever” walls utilize integrated, stand-alone systems that can work together to form a waterproof air barrier for all types of vertical, above-grade wall surfaces, engineered for fast, easy application. (Example: StoGuard) These continuous-insulation (ci) wall systems can provide superior air and weather tightness, long-lasting thermal performance, durability and are available in a wide range of decorative and protective finishes.

Look for PART ONE in our series next week; it will focus on Moisture Control.


New Energy Saving Calculator for Airtight Building Design

Lido Beach Towers in Long Island,
N.Y., a condominium community, used air moisture barriers in a resilient design retrofit that resulted
in energy savings of up to 33 percent as
well as enhanced structural protection.

Lido Beach Towers in Long Island, N.Y., a condominium community, used air moisture barriers in a resilient design retrofit that resulted in energy savings of up to 33 percent as well as enhanced structural protection.

The Air Barrier Association of America (ABBA), in conjunction with Oak Ridge National Laboratories (ORNL) and the National Institute of Science and Technology (NIST) have developed a web based energy saving calculator for building airtightness. This valuable new resource will help the building industry quantify energy savings based on the use of air barriers that increase the airtightness of buildings.

We all know that uncontrolled heat, air, and moisture transfer through a building envelope has a significant impact on energy usage. A comprehensive strategy for concurrently regulating these factors can have a major impact on reducing energy consumption. Air moisture barriers (AMBs) have proven to be effective and economic but now these benefits can be better calculated in advance.

The hope is that there will be wider adoption of air barrier systems in building design thanks to this simple and credible tool that can be employed by architects, designers, and owners to accurately estimate anticipated energy savings if an air barrier system is added to the design. This new energy saving calculator is based on the best science available, it’s easy to use, available to everyone, and best of all – it’s free.


Using Design to Address Sea-Level Rise

The architectural, engineering and construction industries are looking at ways to mitigate sea level rise and climate change in coastal communities.

The architectural, engineering and construction industries are looking at ways to mitigate sea level rise and climate change in coastal communities.

People love being near the water — beach front homes, offices on the Bayfront, cultural and entertainment centers on an ocean or lakeside. The water’s edge is always alluring. In fact, 40% of today’s U.S. population lives on or near the water

Unfortunately, as recent climate-change experts point out, nature seems to have other ideas. What is now perched on the water in many areas, will likely be under water in the foreseeable future.

Even if carbon emission targets and other benchmarks set at the historic Paris Agreement in 2015 are met, sea levels will likely rise 20 inches by 2100. If we continue emitting greenhouse gases, it is more likely to be a 29-inch rise. And, according to a January, 2017 report from the National Oceanic and Atmospheric Administration, some US coastal areas, will experience as much as a 6-foot rise in sea levels by 2100.

If unaddressed, this phenomenon poses an unprecedented human and economic threat. Already, current sea level rise has contributed to more damage in extreme weather events such as Superstorm Sandy, causing massive flooding and infrastructure damage.

Mitigating the Effects of Sea Level Rise

While government and community agencies are now addressing sea level rise issues in coastal areas with plans for levies and sea walls and other means of circumventing water rise, the architectural and engineering community has begun to seriously develop strategies and tactics as well.

Fighting sea level rise from a design perspective boils down to either keeping the water out or designing around it.  Preserving views and water access and maintaining aesthetically pleasing design however can be challenging under the circumstances.

For new and/or existing buildings, resilient design is critical. Using materials that protect buildings from wind and water damage, even elevating buildings above water are certainly valid strategies for addressing sea level rise, but what about entire streets or neighborhoods that are submerged?

As Construction Dive points out, architects, engineers and contractors need to understand the issues and be on the forefront of advocating for design that anticipates and counters potential rising waters on our coasts.


Tallest Tower West of Chicago Topped Off in San Francisco

The 1,070-foot-tall, $1.1 billion Salesforce Tower in San Francisco will be the tallest skyscraper west of Chicago.

The 1,070-foot-tall, $1.1 billion Salesforce Tower in San Francisco will be the tallest skyscraper west of Chicago.

The 1,070-foot-tall, $1.1 billion Salesforce Tower was topped off in San Francisco last month making it the tallest skyscraper in the West, eclipsing the city’s Transamerica Pyramid. It also tops the charts as the most expensive building ever constructed in this City-by-the-Bay “with little cable cars climbing halfway to the stars…”Salesforce, the enterprise giant, will pay close to $560 million over 15 years for the naming rights in this landmark  real estate transaction.

The 62-story, 1.4-million-square-foot building, includes access to the new Transbay Transit Center which will connect 8 Bay Area counties through 11 transit systems. The tower features 13-foot-high ceilings, 10-foot glass panels and metal sun shades at each floor to help regulate the building’s temperature and lighting. Builders are aiming for LEED Platinum certification with sustainable features that include high-efficiency air handlers for increased natural ventilation, under-floor air distribution, and a sophisticated water recycling system.   salesforce-and-its-billionaire-ceo-marc-benioff-are-riding-high-these-days-1

So far, the skyscraper is 70% leased; Salesforce has taken the bottom 30 and top two floors; Bain & Company and Accenture are other tenants. The estimated completion date is late 2017. The signature project was developed by Boston Properties and Hines and is being managed by Clark Construction; the architects are Pelli Clarke Pelli.