Understanding R-Values
For starters, R-Value is the resistance value. What this means is if you put a heat source (sun and radiant heat from outside home) on one side of a chamber and 1 inch insulation on the other side, then R-Value is the resistance to the heat saturation to the other side of that chamber. Simply put, R-Value is the way that professionals and customers have some sort of “apples to apples” to compare when discussing which foam is right for them.
There Are Two Types of Spray Foam: Open-Cell and Closed-Cell
Open-cell spray foam is commonly used in ceilings, walls, and roofs because it has a low density, expands easily, and proper R-value’s can be achieved for about half the price of closed cell foam. Closed-Cell spray foam is more dense and provides a better air barrier and is more resistant to moisture. Professional insulation contractors will typically apply it in crawlspaces, basements and metal buildings.
R-Values by Region
The R-Value required in your home is different depending on how it is applied, what material is used, and what climate zone you live in. Here in Georgia, around Atlanta and north we are in climate zone 3. As you get into north Georgia, we transition to climate zone 4. Code requires an R-Value of R-13 in the wall and R-38 in a ventilated attic using Fiberglass. In climate zone 4 an R-49 of Fiberglass is required to be installed on the attic floor. Insulating with spray foam moves you to a different application of technology. An encapsulated attic is and unvented attic system. The spray foam is installed against the roof deck with code requiring it to be R-20. Code recognizes the performance of spray foam in an unventilated attic system is much greater than fiberglass. This is the reason spray foam in a roof deck only needs to be an R-20 in both climate zone 3 and 4.
The R-Value of 1 inch of open-cell spray foam is about an R-3.4 per inch, while 1 inch of closed-cell spray foam is around an R-7.1 per inch. Remember, closed-cell is much more dense!
Insulating a roof deck with R-20 spray foam exceeds the performance of R-38 so much so, that even in climate zones where R-49 is required, it also exceeds the performance factor there. The reason for this is because of how the spray foam is applied and the technology that is applied. Meaning? You’re migrating your home from a ventilated attic to an unventilated attic using spray foam only at an R-20 and eliminating things like ridge vents, passive vents, and power vents.
Why Does an Unventilated Attic Matter?
When you encapsulate an attic you stop the stack effect, and the stack effect is what puts a negative pressure on your home. A stack effect is when your attic heats up, as it’s traditionally designed, and as air rushes out of your vents in your attic it has to be replaced. Typically the air comes in from the soffits, but soffits are rarely sized correctly, get clogged by debris and painted over as time goes on. The net free area of your soffit vent becomes reduced. Even on new homes, soffits are typically not balanced properly and won’t provide the right amount of air flow. Here in Georgia, we heat up so quickly on the average day that the attic heats up and very quickly begins to pull a negative pressure on the house. (aka the stack effect). As air is rushing up and out, you now have make-up air being pulled in from every penetration, window, door throughout main level of home and basement as well. For homes that are on a crawl space it means that the air from crawl space is being pulled into the home. A large percentage of the air in a home, because of the stack effect, is now air from the crawl space. By properly insulating your home, you are decreasing the loss of air from your home while also improving the air quality inside of it!
