You’ve come to the point in building or remodeling your home where you need insulation, and your contractor is recommending flash and batt for your walls.
You feel confident in your insulation knowledge, but you aren’t really sure exactly what flash and batt is or how it works. Don’t worry, we’ll break it down for you in a way that you can understand.
RetroFoam of Michigan has more than 20 years of experience insulating thousands of homes with foam insulation. While a combination of spray foam and batt insulation isn't a service we offer, we understand the thought of how this method should work.
In our ongoing efforts to educate homeowners, we have put together this article to explain what flash and batt is, as well as how it works and the pros and cons.
Flash and batt is spray foam insulation with fiberglass batts laid over top.
It’s a technique used by some insulation contractors where a flash of closed cell spray foam at 1- to 2-inches is applied in an effort to create an air seal, and then fiberglass batt insulation is put over it.
It’s typically done in walls.
The theory is that the layer of closed cell spray foam gives you an air seal, and then the fiberglass on top of that adds the R-Value needed to get to the prescriptive code.
With most closed cell spray foam insulations, you need a minimum of 2-inches to create an air seal. There are some manufacturers that require 3-inches for an air seal.
That 2-inches of closed cell is about an R-14 in the walls, and the prescriptive code in Michigan for walls in new construction is R-21. The contractor adds the fiberglass just to hit the prescriptive code in an attempt to cut costs.
Although this method is one way to meet code and cut costs, there are problems with this model that we will get into shortly.
R-Value is the capacity of an insulating material’s resistance to heat flow.
That means the higher the R-Value, the greater the insulating power of the material. While it’s important to understand R-Value, it isn’t always the revered determiner of insulation most people think it is.
Insulation is much more than just a number since heat flows in and out through radiation and convection. Heat loss through convection, or airflow, can account for around 40 percent of total energy loss in your home.
This is an issue if you are only using the prescriptive code for R-Value to choose your insulation.
This hybrid method could work if it was installed properly, but many contractors who recommend this install less than the required 2-inches of closed cell to create an air seal.
On the flip side of this, if the contractor applied 2-inches of closed cell, you wouldn’t need the fiberglass to pass code when using the performance method because the spray foam created a total air seal. The prescriptive code focuses on the R-Value needed for the area.
For example, R-21 is what is required for Michigan. The performance method helps meet code for insulation materials like foam that creates a total air seal in the home. This means the wall with 2-inches of closed cell or 3-inches of open cell that is less than the prescriptive R-21 will still pass code since it will perform at that level or above.
Here are some of the pros and cons of flash and batt insulation.
Just like any insulation project, the size of the area to be insulated determines the cost.
The cost to insulate the wall cavities in a 2,000-square-feet home with flash and batt would be between one-third to half the cost of insulating properly with spray foam alone.
Sure, everyone wants to save a few bucks, but you will need to decide if it is worth it, considering the potential long-term problems that can arise when an air seal isn’t achieved. It’s also important to note that the amount of spray foam insulation needed for this method passes code alone due to its performance.
Now that you have read all about this method, you may be deciding the flash and batt insulation problems outweigh the good.
If you’d like to learn more about the benefits of foam insulation on its own, check out the Learning Center on our website.
Flash and Batt Insulation Problems: 4 Issues You Want to Avoid
Spray Foam Insulation Code Requirements: How to Pass Code Without Meeting Prescriptive R-Value
Michigan Insulation Code: New Home Insulation Requirements