Flash & Fill / Flash & Batt –
Using 2 Different Types of Insulation for Lower Cost
Foam it Green spray foam insulation can be combined with other insulation to make a powerful hybrid method. You can get similar results as doing all closed cell foam but with less cost. It’s a great way to get the benefits of closed cell spray foam and save money on insulation at the same time.
You use 1 or more inches of Foam it Green closed cell spray foam and then fill the rest of the cavity with lower cost insulation for r-value.
You get the high r-value, tight building envelope and water resistance by using Foam it Green closed cell foam first. Then the less expensive insulation adds some r-value without having its performance destroyed by air flowing through it.
Flash & Fill:
When you use Foam it Green Closed Cell Spray Foam for the first 50% of the R-value and then use Foam it Green Anti-Microbial Open Cell Spray Foam. It’s the most convenient way to save energy and money.
- Fast – Sprays right on
- Easy – No cutting batts
- Highly Mold Resistant
- A Tight Air Barrier throughout the wall
- Higher Compound R-value than using other forms of filler
Flash & Batt:
When you use Foam it Green Closed Cell Spray Foam for the first 50% of the R-value and then use Fiberglass (or another low cost insulation) to get the air barrier and high starting r-value and then add in more r-value.
Some people can use just 1 inch of Foam it Green closed cell spray foam insulation and others need more.
It depends on the project and where you live.
According to building scientists, the general rule to follow is:
If you heat during the winter, you need 50% (or more) of the total R-value of an enclosed wall or cathedral ceiling’s insulation in Foam it Green closed cell spray foam.
Here’s why. The dew point happens when hot air meets cold air. The cold air cannot hold the moisture in the warm air, so it turns to water and drops from the air, creating condensation.
If this condensation happens in Foam it Green closed cell spray foam, the condensation has nowhere to go. If the dew point happens in the open cell foam or fiberglass, you’ll have condensation between the foam and the other insulation.
Isn’t that taken care of with a vapor barrier?
Vapor barriers stop vapor transfer through the wall. That is different. In this case, the dew point creates condensation between the vapor barriers.
This happens in all walls, but when you don’t have a tight air seal, your loss of energy through the walls keeps “drying” out your insulation (not completely, and that’s why people find mold in their fiberglass walls).
When you create the tight air seal with Foam It Green closed cell spray foam insulation, you’re no longer losing the energy from your home via air flow through your walls. This is a GREAT thing. Now you’re actually saving energy. You just need to make sure you accommodate for the dew point so you don’t have moisture issues.
To calculate what you need, you need just 2 numbers:
The number of inches of space within the enclosed wall cavity.
The R-value per inch of the materials you plan to use to fill the wall. For example, one inch of Foam It Green closed cell foam is R-7 and Fiberglass batts are approximately R-3.5 per inch. One inch of Foam it Green Anti-Microbial Open Cell Spray Foam is R-4.
Then determine the ratio of closed cell foam to fiberglass or other insulation to make sure the total R-value of Foam It Green Closed Cell is 50% or more of the total R-value.
Below are some common examples:
- 2×4 walls = 3.5 inches of space
1 inch Foam it Green Closed Cell = R-7, 2.5 inches fiberglass = R-8.75. R-7 isn’t 50% of the wall’s r-value, so you DON’T want this if you heat in the winter.
- 2×4 walls = 3.5 inches of space
2 inches of Foam it Green Closed Cell= R-14, 1.5 inches fiberglass = R-5. The Dew Point will be in Foam it Green and thus minimize moisture issues.
- 2×6 walls = 5.5 inches of space
2 inches Foam it Green Closed Cell = R-14, 3.5 inches fiberglass = R-12.25. The Dew Point will be in Foam it Green and thus minimize moisture issues.
- 2×10 Rafters (cathedral ceiling) = 9.5 inches of space
3.5 inches Foam it Green Closed Cell = R-24.5, 6 inches fiberglass = R-21. The Dew Point will be in Foam it Green and thus minimize moisture issues.
Learn More About Closed Cell Spray Foam>>