The views expressed in this post are based on our personal experience + industry research. There is more information on this subject linked throughout to help you make an informed decision about your project.
The first home that we used spray foam in was our post frame barndominium which you may also know as the Mad County Build. There are nearly 200 videos of this DIY build project on YouTube which was built from July 2019-February 2022 by Paul, MR Post Frame himself.
Today, it's our primary recommendation for all of our clients when it comes to insulating their exterior walls + roof. We only recommend using closed cell spray foam, + do not recommend using open cell or combining open/closed.
Reason #1 - R-Value + Barriers
All of our projects come with the recommendation to use 3 inches of CLOSED cell spray foam on all exterior walls + roof when budget allows. This acts as a one and done way to insulate your walls and give you required R-Value, vapor barrier, and air barrier that is needed.
Did you know your vapor barrier location is dependent on where you're building? Closed cell spray foam prevents making a mistake regardless of your climate.
Reason #2 - Keeps Everything Out
Closed cell spray foam has a sealing effect that is as it's name suggests- closed. This makes for an amazing barrier between the great outdoors and the inside of your home. It's the only type of insulation that fills the "nooks and crannies" in your walls making it more difficult for bugs, water, etc. to find their way in.
Reason #3 - Efficiency
Closed cell spray foam provides whole home efficiency like no other insulation. This aids in keeping utility costs low.
It prevents temperature fluctuations meaning less run time for your heating/cooling systems. Once installed it does not sag or deteriorate even in extreme heat or cold.
Reason #4 - Enhances Structure
We specialize in post frame barndominiums and love how closed cell spray foam adds structural integrity to our builds. It acts like a glue that locks everything in place.
A Few Considerations...
Hiring a good spray foam contractor is key to your success with this product. If something doesn't feel right, ask more questions. Don't let someone convince you to go a certain direction based only on cost- look at the real pros and cons.
Don't mix and match. Whatever type of insulation you use stick with it. We learned that the hard way which is why we are so dedicated to providing quality education around the subject of insulation. Our original spray foam contractor stated (on video) that it was ok to add a fiberglass bat on top of the spray foam which caused a massive condensation issue. We had to remove all drywall on exterior walls, pull out the bat, add more spray foam, and re-drywall. Even though it had only been installed that way for a few weeks we had bats soaking wet and mold forming inside of the wall cavity. It was a tragic delay and huge hit to our budget.
Since you can seal off your attic from your walls it is acceptable to use a different type of insulation in each location. We have blown in fiberglass in our attic and many of our clients opt for that same method.
Check out these resources to further your education on the matter:
Want to see a different perspective? Check out Megan's thoughts on why they did NOT use spray foam over at the Barndominium Tour website.