SHOULD SYNTHETIC UNDERLAYMENT BE BREATHABLE ?
Understanding the Role of Synthetic Roofing Underlayment and Roof Ventilation
To address this question, it's important to understand the underlying concerns around roof ventilation and moisture management.
Concerns often revolve around the potential risks associated with a poorly ventilated roof, including moisture buildup, decreased energy efficiency, damage to roofing materials, and the development of issues like ice dams or mold. Proper roof ventilation is absolutely crucial for maintaining a healthy and durable roofing system, but let’s not create a misplaced alignment between this concern and your roofing underlayment choices.
The amount of airflow needed to achieve proper ventilation depends on various factors such as attic size, climate, and the type of ventilation system installed. Generally, building codes recommend a minimum ventilation rate of 1 square foot of ventilation opening for every 150 square feet of attic space. (consult your local building codes) , roughly equal to a perm rating of 150 *perms per square foot
Synthetic Roofing Underlayment also has a perm rating. A lower perm rating indicates less vapor escape, while a higher rating allows for more. Most underlayment strive to be less than 1 perm, as a water barrier, however some roofing underlayment products tout the benefits of breathability and design a perm ratings of around 4-7perms.
At best the underlayment might contribute <7 perms of the 150perms per square foot need.
It's like bringing a water balloon to a 3-alarm structural fire.
Conclusion: It is best to rely on a properly designed roof ventilation system to achieve adequate ventilation, while roofing underlayment products can focus their primary purpose as protection for the roof deck, safety for the installers and serving as a secondary barrier against the elements. The more waterproof and vapor proof, the better.
Tuffdry offers two types of synthetic underlayment, the first is synthetic underlayment that is mechanically nailed to the roof substrate as well as peel and stick options depending on your needs. Reach out to us if you have any questions our would be interested in a sample
*perm - permeability measurement of vapor transmission against an ASTM E96 standard. How much vapor can pass through