Currently, the construction industry enjoys virtually no consensus regarding building paper, the stuff that wraps the house. Since major technological advances in the fields of building science and home performance, a “unified field theory” of the building envelope eludes us. Instead, we are faced with a number of differenting approaches.
Those who advocate for the old methodology of 15lb. melt and wood siding ignore the rising cost of energy. More airtight building wraps require a breathable layer and / or drain mat that allows the backside of the siding to drain and dry (a feature that is now part of code for new homes) as well as additional care for air quality. Breathable wraps used in conjunction with “rain screen” systems combine features of these methods but leave unanswered the question of air permeability as it relates to energy efficiency. Passive House standards require that a airtight, vapor-permeable envelope be created, with indoor air quality maintained by an HRV system.
The point is that every one of the four paths mentioned above represents a fundamental disagreement about the important aspects of the building envelope. It is a classic example of “do you walk to school or carry your lunch?” These different methodologies offer offer divergent answers to questions about the envelope. Actually, they do not even ask the same questions about the functionality of the envelope.
This article uses the analysis of different types of building paper / house wrap to define the real question: How do we want our structures to perform?
The building envelope should provide shelter. It should be durable. It should be made of materials that are efficient in their assembly and energy consumption. But that is about the end of common ground. Anything more specific requires a choice that weights the following values relative to one another: cost, insulating capacity, air-tightness, vapor permeability, sustainability, and aesthetics.
Whatever choice is made needs to fall in line with larger home performance requirements of efficiency, comfort, safety and durability. The relative mix of these requirements differ from person to person, and the industry offers building papers and envelope systems that fit better with one set performance criteria than another.
But the most important thing to emphasize is that the house performances as a system. The envelope is just the skin.
Only when a type of paper conflicts with the design and performance characteristics of the house can there be real trouble. An example: when an air tight, vapor semi-permeable house wrap is used with no equipment installed to address air quality, both in terms of pollutants and humidity differentials. Not only can the air get stinky and dangerous, but also the dew point can form inside the wall cavity. Another example: siding systems that leak (all siding systems) without a drain layer behind them to avoid water build-up inside the envelope.
So decide what is important to you about how your house performances, understand the performance characteristics of different house wraps and make a good match to avoid disaster.