Vapor Barrier where multiple types of insulation are used?


Based on Ashrea standards it is now common practice in many areas to have multiple types of insulation. In these settings where does the Vapor Barrier go? I ask this because many rigid insulations have a vapor barrier pre-installed. If this wall was in a colder climate common practice would say to install the vapor barrier on the inside face of the wall. However as many polyiso ci have a pre-installed vapor barrier, would this create a situation where moisture is sandwiched within the wall assembly?

Hi @karen.wenschhof !

So sorry for the delay on this, I did some research to find some websites that explained the answer to your question and failed to respond! Just FYI, I based my research on Huber’s Zip system so if you have more questions, their website is very helpful!

A product like the zip system doesn’t include a pre-installed vapor barrier, it only includes a rain/weather barrier on the exterior of the system (which is what the green portion is that you see when it’s being installed). In a warm climate zone like Florida, a vapor barrier would need to be installed on the outside of that system (on the warmer side of the wall) while in a colder climate like Colorado, it would be installed on the inside of the wall just as you stated.

If there are any other products you had in mind, please let me know. I hope this helps! Thanks!


@karen.wenschhof there was also a similar question about vapor barrier posted awhile back.
You can check out that post at the link below:

Like @coachrebeccasmith said exterior plastic/papers (like in zip systems) and Tyvek, or liquid applied barriers (like in EIFS installation), are all examples of weather barriers. They stop rain from entering the building. The vapor retarder (sometimes called vapor barrier, but more accurately called a retarder) prevents moisture from entering and getting trapped in the wall due to temperature differentials between the exterior and interior, conditioned areas. It’s always installed on the warm face of the wall.

Hope this helps!