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 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 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.

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  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.

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.

Today’s Building Codes Call For Advanced Air & Moisture Barriers

Building codes today demand high-caliber, hi-tech air & moisture barrier systems that are versatile and trustworthy.

As building codes become more complex in their requirements for protection against moisture damage and unwanted air movement, contractors need systems that are quick and easy to install while still providing excellent performance over a building’s lifetime. Air and moisture barrier systems (AMBs) can offer seamless protection for entire wall assemblies, regardless of region or climate.

One such new and improved product is StoGuard® VaporSeal™. A high-build, vapor permeable, fluid-applied membrane, it is used to provide backup protection for porous cladding materials. It also protects joints and rough openings behind all types of claddings, and provides an air barrier beneath continuous insulation to meet prevailing energy codes.

The reformulated product offers the following:

  • A Class I Vapor Barrier (retarder) with high build at 40 mils DFT(dry film thickness)
  • A water-vapor permeance less than 0.1 perm
  • Easy and fast application with airless spray equipment up to 80 mils WFT (wet film thickness); it can also be roller-applied
  • Elongation greater than 500%
  • Enhanced low-temperature crack-bridging

VaporSeal is NFPA 285 compliant and resists mold growth. It boasts a water-based, low-VOC formulation that is environmentally friendly and easy to clean up. Designed for application over CMU and sheathing, it can also be used under claddings such as metal panels, cement board, vinyl, wood, brick and stone.

Research has shown that controlling moisture and air leakage through the building envelope is critical to achieving high building energy efficiency. Unlike building wrap barriers that are penetrated by staples and fasteners used for their attachment, so-called seamless systems utilizing products such as StoGuard® VaporSeal™, better control air and moisture to improve building performance and occupant comfort.

How to Meet Today’s Building Codes with the Right Continuous Insulation

A cutaway drawing of the protective layers of StoTherm ci XPS insulation with an exterior Lotusan coating.

Many of today’s building designers and owners find themselves contending with the need for an advanced insulated wall cladding that meets the country’s increasingly rigorous IBC building codes such as Title 24, IBC, IECC and ASHRAE 90.1. What they want is efficiency, durability and a flexible range of exterior appearances. Sto’s answer? StoTherm® ci XPS continuous insulation.

StoTherm ci XPS is an integrated, continuous-insulation wall system that is air & moisture-controlled, thermally-efficient and highly durable. It helps cut energy costs, reduces maintenance expenses by extending the building life cycle and adds value by offering designers a variety of aesthetic options thanks to a wide range of decorative and protective finishes available in virtually unlimited colors. It checks all the boxes on today’s exterior specifications requirements list.

You’ll find more specification information on both ARCOM Masterspec Section 072419: Water-Drainage Exterior Insulation and Finish System (StoTherm ci Wall Systems – EIFS) and BSD Speclink-E Section 072400: Exterior Insulation and Finishing System (StoTherm ci systems).

The newly-renovated Nippert Stadium at the University of Cincinnati incorporated StoTherm ci XPS in several of the wall structures.

The newly-renovated Nippert Stadium at the University of Cincinnati incorporated StoTherm ci XPS in several of the wall structures.

StoTherm ci XPS is a highly energy-efficient system thanks to the combination of a fluid-applied StoGuard air & moisture barrier and extruded polystyrene insulation with installation-friendly components that eliminate heat-dissipating thermal bridging from mechanical fasteners and minimizes heating and cooling costs. It requires only one trade to install the entire system, which both cuts the time to build and lowers overall construction costs. And its low allowable deflection value of L/240 compared to L/360 for stucco and L/620 for brick facilitates lightweight construction and produces a lower cost per square foot.

This makes the StoTherm ci XPS system an ideal alternative to stucco and brick systems. Why? Faster, easier installation; high durability with a maintenance-friendly exterior finish that looks great and lasts. The economics are favorable, too; XPS material costs are typically lower than insulated stucco, brick or metal panel.

StoTherm ci XPS is part of StoCorp’s range of continuous insulation systems including EIFS, Stucco, Cement board stucco and Sto Panel (prefabricated) wall systems. The latest news is that the company is now partnered with two of the insulation industry’s leading vendors, Owens Corning and Dow as suppliers for a key component of the StoTherm ci XPS system. This now means that Sto customers will have two options when choosing the durable, high-R-value rigid foam insulation that resists water absorption and significantly contributes to the Sto ci wall.

This development makes it even more apparent that today’s StoTherm ci XPS is a true problem-solver. The news for architects and contractors is that the product now deserves a second look.