Polyiso is used on masonry walls in either exterior or interior applications and can deliver high R-values with a thinner profile. Photo courtesy of RMax, Inc

Wall Insulation
Insulation can be placed in a structural wall or on an exterior face of the wall. Insulation batts with high R-values, are commonly placed in-between stud walls. By placing board insulation with high R-values across the exterior face of a building, the professional can prevent the thermal bridging caused by heat loss through the structural members. As much as 1/3 additional insulation value is gained by covering the exterior structure with insulation. Often several layers will be required to obtain larger R-values and these should be carefully overlapped to provide greater thermal protection. Insulation can also be sprayed into wall cavities of existing structures which will improve thermal performance values in the existing structures. Spray-in fiberglass insulation can also reduce waste on a construction site as the excess material can be re-used by the installer.

Water should be kept out of buildings through the wall system but if water or moisture gets into a building, it has to get out and in cold climates, have enough room to freeze and thaw before it damages a building system. Air barriers restrict the flow of air and a vapor barrier resists the flow of moisture in building materials.

Water-resistant or moisture barriers are designed to keep liquids from pelting rain or snow, from penetrating a building wall system. Sometimes all three are in the same product.¹⁵ A vapor barrier or vapor diffusion retarder is described by the US Department of Energy, Energy Efficiency and Renewable Energy (EERE) division as a material which reduces the rate at which water vapor can move through a material. The "ability of a material to retard the diffusion of water vapor is measured by units known as "perms" or permeability. A perm at 73.4 degrees Fahrenheit is a measure of the number of grains of water vapor passing through a square foot of material per hour at a differential vapor pressure equal to one inch of mercury. Any material with a perm rating of less than 1.0 is considered a vapor retarder."¹⁶ Insulation materials need to have high perm rates and allow moisture to go through the material to prevent mold and mildew in wall cavities, or on interior finishes.

Sometimes, interior finishes such as vinyl wall coverings, have impeded the flow of moisture through a building which can causes mold if the ventilation system was not designed to accommodate this surface application. In these cases the location of the vapor barrier can assist with mold growth. Manufacturers will provide a numbering system to denote whether the vapor barrier is part of the insulation board and where it is located in the sandwich of the insulation panel. In cold climates, the vapor barrier is placed on the warm side of the wall, towards the interior surfaces, however, each climate zone and occupancy requirement must be carefully analyzed. The EERE provides a map of the U. S. with recommendations for the location or proper placement of a vapor barrier.¹⁷

Insulation in ductwork, or used to protect water piping, will also control condensation caused by humidity, inadequate ventilation and the movement of air from the outdoors through conditioned spaces. Plumbing, ventilation, mechanical heating and cooling ducts can all "sweat" moisture into the building envelopes. Architects and mechanical engineers know the importance of the integration of the mechanical system with the designed occupancy of a new building. Accordingly, when a building is retrofitted for new uses, all of the components of the mechanical system, the interior finishes, and the structural cladding of a wall system should be evaluated for moisture content, the prevention of moisture flow as well as moisture protection.

Sheathing
There is a difference between insulation and sheathing. Sheathing has very little thermal value and will not prevent thermal bridging and heat loss from a structural frame. It can add to the moisture control and construction scheduling of the wall system. "Glass-mat gypsum exterior sheathing has a 12-month exposure warranty and can help with the scheduling of construction projects," stated Douglas C. Gehring, P.E., CSI, of CertainTeed Gypsum, Inc. Sheathing is used for walls, and for exterior soffits as well as for interior wall boards. Glass-mat gypsum sheathing is commonly used as a component of an exterior fire-resistance-rated wall assembly. It must be covered with an approved water resistive barrier and an approved exterior wall covering. Glass-mat sheathing is inherently moisture and mold-resistant.

Glass-mat fiberglass sheathing as part of the wall system for Asa Flats designed to LEED Gold Certification. Photo provided by CertainTeed Gypsum

Water is expelled swiftly through these polyester-mesh weeps. Inside the cavity are other components that drain and direct the water toward the weeps, and prevent "damming" from mortar-droppings. Photo courtesy of Mortar Net® USA

Flashing
As demonstrated in wall tests, when it rains, water penetrates most wall enclosures. Even the tightest building envelope has seams at corners, windows, vents and any junction between one type of cladding material with another. Manufacturers as well as professional manufacturers' associations maintain libraries of proper flashing details which will assure that rain will "go away" while allowing for water vapor to move throughout the structure as necessary.

Conventional flashing systems for cavity walls include several materials all shipped separately to a site. Although easy to draw on a professional's computer system, in reality, the installer has to handle long rolls of flashing membranes that come in a roll, weeps, drip edges and a termination bar in an uncontrolled outdoor environment. Conventional flashing usually takes two people to install and in a multi-storied building the installation can be at worse precarious, and at best imprecise, particularly at corners. Flashing must be cut, mitered and placed in a sequence which requires overlapping in the direction of water flow to channel water away from the interior structure.

A sample of an integral flashing system. Photo provided by Mortar Net® USA

New products combine all of the flashing components into one flashing material which is precut into segmented pieces. As shown in the case study for Asbury Park, these flashings include a termination bar, drainage matte for mortar-droppings, edge dams, no-clog weep tabs, stainless steel drip edge and clearly-marked lap-joints for precise placement even on tall scaffolding. One person can install this segmented flashing which also includes corner angles and lap joints. Controlled flashing will leave a crisp line in a building façade. Flashing can become an unwelcome design element for many architects, but if ignored, can shorten the life of a building façade.