Flash & Batt

Flash & Batt is a very popular way to insulate walls and buildings. It's a great way to get the benefits of spray foam and save money on insulation at the same time. You use 1 or more inches of Foam it Green and then fill the rest of the cavity with fiberglass or another form of insulation. You get the high r-value and tight building envelope from Foam it Green. The fiberglass adds some r-value without having its performance destroyed by air flowing through it.

Some people can use just 1 inch of Foam it Green 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 fiberglass, you'll have condensation between the foam and the fiberglass batt.

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 spray foam, 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 for YOUR project, you need to determine a few numbers.

1) The number of inches of space within the enclosed wall cavity.

2) The R-value per inch of the materials you plan to use to fill the wall. For example, Foam It Green is R-7 per inch and Fiberglass batts are R-3.5 per inch.

Then determine the ratio of foam to fiberglass or other insulation to make sure the total R-value of Foam It Green is 50% or more of the total R-value. Below are some common examples.

• 2x4 walls = 3.5 inches of space.
  1 inch Foam it Green= R-7, 2.5 inches fiberglass = R-8.75 This isn't 50% of the wall's r-value, so you DON'T want this if you heat in the winter.
• 2x4 walls = 3.5 inches of space.
  2 inches of Foam it Green = R-14, 1.5 inches fiberglass = R-5 The Dew Point will be in Foam it Green and thus minimize moisture issues.
• 2x6 walls = 5.5 inches of space.
  2 inches Foam it Green = R-14, 3.5 inches fiberglass = R-12.25 The Dew Point will be in Foam it Green and thus minimize moisture issues.
• 2x10 Rafters (cathedral ceiling) = 9.5 inches of space
  3.5 inches Foam it Green = R-24.5, 6 inches fiberglass = R-21 The Dew Point will be in Foam it Green and thus minimize moisture issues.

To learn more about vapor barriers in walls, please see the following iinks and always make sure to follow your local building code regulations:

• Vapor Control Layer Recommendations
• High-R Wall-09: Flash-and-Fill Hybrid Wall Construction
• Understanding Vapor Barriers