Why Doesn’t Open-Joint Cladding Work for Every Build?

Open-joint cladding systems can be a controversial topic. Although they allow more rain and air into the wall assembly, they actually tend to outperform non-exterior wood cladding systems because the increase in air allows for more drying capability.

Having said that, the concept of open-joint cladding doesn’t work for every project. Dr. Joe Lstiburek breaks down the reasons in this episode of A Cup of Joe, as well as the science behind how it works.

Finally, he’ll cover the products that need to be in place to ensure your building has the protection it needs from water, air, and UV exposure.

Here’s a summary of Dr. Joe’s thoughts and suggestions on open-joint cladding:

  • An open-joint cladding system has far greater drying potential than a non-open-joint system.
  • This is due to the air circulation that’s possible behind the system; while more rain and moisture can get in, this is offset by the drying capacity.
  • The concept of compartmentalizing and sealing cladding systems comes from almost 50 years ago, and a belief that if we created a sealed cavity and the air entered, the cavity would be pressurized, and the pressure behind the cladding would be the same as the pressure on the face of the cladding – this is where the term pressure equalization

how pressure equalization works

  • This concept does work – however, it only works for very small spaces.
  • Why? Because air is compressible, and the air on the face of a building, facade, or surface fluctuates rapidly, and the pressure in a large cavity doesn’t react as quickly to the changing pressure on the face.
  • This leads to a non-pressure equalization response where we can have the pressure in the cavity be out of phase with the pressure on the face.
  • As a result, this will actually increase rain penetration.
  • But in small cavities, open-joint cladding works brilliantly. 
  • Two other areas to be aware of are aesthetics and protection from ultraviolet (UV) light.
  • Modern architecture pushes the boundaries of the beautiful characteristics open-joint cladding offers, but designs need to ensure the sheathing and insulation behind it are not visible.
  • A form of protection must be provided there, such as a membrane or coatings on the sheathing and/or the rigid insulation.
  • Most importantly, the chosen protection needs to be resistant to UV light.
  • So, you want a protective product that hides sheathing and insulation, resists UV exposure, and will last a long time – you don’t want a 50-year cladding system with a 10-year protection layer behind it.

Learn more about open-joint cladding systems

About Dr. Joe Lstiburek 

Dr. Joe Lstiburek is the founding principal of Building Science Corporation, one of the most influential, innovative, and respected building science firms in North America. Dr. Lstiburek’s work ranges widely, from providing expert witness testimony to overseeing research and development projects to writing for the ASHRAE Journal. His commitment to advancing the building industry has had a lasting impact on building codes and practices throughout the world, particularly in the areas of air barriers, vapor barriers, and vented and unvented roof assemblies. His commitment to education earned him the hailing, “the dean of North American building science” by the Wall Street Journal. Dr. Lstiburek holds a Bachelor of Applied Science in Mechanical Engineering, a Master of Engineering in Civil Engineering, and a Doctor of Philosophy (Ph.D.) in Building Science. Get the full scope of Dr. Lstiburek’s work, accolades, and contributions to the industry over at Building Science Corporation.