The Perfect Wall Concept and resulting Perfect Wall should be in your best practice “tent.” If not, your tent will be filled with more than just the camel’s nose. The Camel nose metaphor is “a situation where permitting some small, seemingly innocuous act will open the door for larger, clearly undesirable actions.” One harmless act or change with a product, complex wall design or its installation can render it ineffective and unhealthy. The Perfect Wall Concept is relatively simple, effective and constructible.
One would think the concept is common knowledge after almost a decade of its promotion by Dr. Joe Lstiburek and scientifically verified by Dr. John Straube. But according to ongoing installation and designer detailing problems, it is not. More verifiers (Consultants, Cx Agents) are being utilized to make the design and construction process accountable.
The Perfect Wall Concept protects and insulates the weather resistant barrier, provides an effective life cycle performance, keeps moisture and condensation out of the building and can be used in any climate. The concept is adaptable to roofs and foundations, providing the same benefits. It can be ventilated or a structural insulated panel (SIP). See included Building Science.com diagram.
Ventilated wall or cavity allows more design flexibility than a SIP system. It is a necessary design component of the perfect wall and it is a simple concept. The ventilated cavity wall has been utilized successfully by this author since the 1970s to protect buildings by removing unnecessary moisture from the cavity.
The Rainscreen is what I consider a high performance ventilated wall that adheres to the Perfect Wall Concept. When energy efficiency requirements were applied and scientifically documented by the Canadians they started calling it the rainscreen. The weather resistant barrier became air tight and the insulation moved to the cavity, providing more efficient continuous, protected and uninterrupted insulation.
The pressurized rainscreen controversy has purposefully been excluded from this article. There are advocates of the system, but this author finds the approach unnecessary in climate zones 2-5 (if not all) and complicated with conflicting opinions by building science advocates.
The rainscreen is the Perfect Wall. The following Perfect Wall has developed over the last seven years as the best practice for exterior wall design. Starting from the exterior face and moving toward the interior, the components or layers are…
Cladding provides the exterior wall’s durable protection, primarily, from windblown debris and ultra violet light degradation. The Perfect Wall allows the use of any type of cladding.
The responsibility of the Air or Drainage Cavity is to ventilate and drain, removing unwanted moisture quickly. The air cavity, vented from the top and bottom, allows free movement of air to dry out damp surfaces. The cavity separates the cladding from the thermal barrier. The cavity also allows for deviations of construction tolerances such as brick, widths varying from 3/8” to ¾”.
The Thermal Barrier is to be continuous, connected to roof, slab and basement insulation, adjacent to and protecting the weather resistant barrier from the climate. It should be in one location, not two; ensuring moisture condensation is on the exterior, minimizing installation expense and protecting it from future building renovations or additions.
The Weather Resistant Barrier (WRB) supported by a substrate is to be in one location only, minimizing redundant barriers and installation errors. These components should always interface with the roof, foundation and basement WRB to provide a continuous air and moisture protected building. Its perm rating should always be similar to its substrate’s, minimizing destructive condensation within in the wall.
Structure supports the wall components and roof structure. It can be metal studs with gypsum sheathing, CMU, etc...
Interior Substrate such as gypsum wall board allows moisture and air movement and supports finishes such as latex paint, wood paneling, etc.
Currently there are efforts being made to combine the layers noted above for improving installation time. There are pros and cons depending on how they are detailed.
The actual design of the Perfect Wall components should always include a basic understanding of building science, constructability, construction tolerances, owner maintenance requirements and material durability to name a few.
We will describe each of these Perfect Wall layers more thoroughly in future articles.
The Perfect Wall is the best practice for ninety percent of the building enclosures. It helps us design effectively for any climate change even though we have 6000 years of limited written documentation. Build your reputation and leave a sustainable, effective building for future generations. Adhere to the Perfect Wall design principle, reject those camel noses.
More best practices to come. If you agree, share this article. Let's improve enclosures together.