Open Cell Spray Foam Insulation & Closed Cell Spray Foam Insulation
Both closed cell spray foam and open cell spray foam insulation can be used effectively in commercial building designs to allow the building to achieve energy efficiency and consistent performance. When applied on the interior, open cell spray insulation provides performance advantages that differ from those of closed cell spray foam used on the exterior. Architectural firms can specify both the building envelope for a total performance option.
Open cell foams are permeable to moisture and impermeable to air. Although open cell foam costs less than closed cell foam, it has a lower R-value per inch, so a thicker layer is required. If the framing members are deep enough to accommodate your required R-value, open cell foam may end up costing less.
Half-pound foam, also known as open-cell foam, has a density of about .5lb per cubic foot and an R-value of 3.5 or 3.6 inch. Open cell foam is relatively vapor permeable. Three inches of open-cell foam have a permeance of 16 perms.
Open Cell Spray Foam Interior Applications
- Can be installed at a significantly lower cost and target the same specified R-value*
- Can achieve greater R-value* if not restricted by space
- Lower raw material/resource use
- Permits bi-directional drying
- Will accommodate long-term creep and seasonal movement
- Hydrophobic material
- Air barrier and insulating material
Open Cell and Close Cell Differences Explained:
Open cell foam is typically R-3.5-R-4.0 per inch and seals walls entirely. Closed cell foam is typically R-6.0-R-6.5 (aged) and seals walls entirely. So why even bother with Open cell foam if closed cell foam insulates so much better? Open cell foam lends itself to applications where space is not limited, like in an attic. However the real reason for using one over the other is Vapor. Vapor is the microscopic droplets of water in the air all around you. Closed cell stops vapor transmission which is good, in certain circumstances. In other circumstances you want vapor to be able to “escape” any cavities such as your walls. If you are thinking “well if I seal it with closed cell foam vapor will not get in there to begin with.” You are wrong. We are speaking of microscopic moisture. The stuff you exhale, the steam off your spaghetti noodles and the humidity the weather man talks about. Have you ever seen a fogged up piece of glass on a window where the fog is trapped between the paines? If moisture can get in there it can get into your wall. Please don’t trap the humidity in there because you need that wood in your wall to keep your house standing in the upright position for years to come. We have created a simple rule. Open cell on Wood, Closed Cell on metal or concrete. You may also use Open cell on concrete but typically we see concrete as a basement wall in a home and these walls are typically below grade and they usually wick moisture into the living space. Closed Cell foam is a great product for stopping the moisture entry into the space, Open Cell will work also but it will not block as much moisture entry into the space.
It’s important to note that open cell foam is an air barrier. Many people take its name – “Open Cell” – to mean that the cells are wide open for air to freely move through the foam. This is not true. Typical air permeance for open cell foam is around .005 L/S/M2 (liters per second per square meter) under 75 Pa pressure at a depth of 3.5” which is great if you want to allow vapor movement (drying). Closed cell is less than half of that at the same R-value which is great for locations where you want to help stop vapor movement (prevention). Both of these rates are incredibly small and undetectable by humans without the use of measuring devices.
R-values of closed cell foam also change over time, while the change in R-value of open cell foams over time is immaterial. Closed cell foams have a high initial R-value right when they are installed because the blowing agent used fills the cells with a gas that is less conductive to heat flow than the air we breathe. Over time (usually a month or two) the gas in the cells will diffuse into the atmosphere and will be replaced with plain old air. This lowers the R-value to an aged value in the 6.0-6.5 range.
Closed cell foam is always more expensive per “R”. So, you could expect an R-13 of closed cell to be more expensive than R-13 of open cell. This is simply due to the fact that plastic costs more than air. There is much more plastic in closed cell than in open cell. It takes three times the amount of chemicals to make a board foot of closed cell foam as it does to make open cell foam. The blowing agent in closed cell foam is also much more expensive than the water used as the blowing agent in open cell foam.
Moisture permeability is the most controversial characteristic of these two insulators. Moisture permeability is measured in perms and represents how much moisture can move through a given material. A perm is defined as a grain of water per hour per square foot per inch of atmospheric pressure. For purposes of this discussion, let’s just say that a perm is the amount of water on a small pinhead. The higher a perm rating, the greater the amount of moisture that can pass through the material. Open cell foam typically has a perm rating of around 15 for 2” depth. Closed cell foam typically has a perm rating around 1 perm for 2” of depth. For comparison purposes, unfaced fiberglass has a perm rating over 100 for an R-13 batt.
Don’t I want to get the most R-Value in my wall possible? If you can afford it, sure!
Lets do some math before I just answer that question and let you decide. The answer is not as cut and dry as you would expect. R value = 1/U value or by doing some algebra we can say 1/R value = U. We’ll get to what is U value in a second. So you want R19 Walls because its your house and you are special. Cool. Lets see how this plays out compared to a normal R13 wall. That R19 wall is going to cost more in lumber and insulation materials.
R30 Wall 1/19 = .0526315789 Uvalue. (Most decent windows are .3 Uvalue)
R13 Wall 1/13 = .0769230769 Uvalue.
So what? What is Uvalue.
Ok so now its time to explain what the significance of Uvalue is. Uvalue is the conductivity rate mathematically. So take your delta T (also known as the difference in temperature from outside to inside the home) x the Uvalue of the wall x the area of the wall and that will tell you how much heat enters in the summer and how much heat leaves in the winter.
72 deg inside and 52 deg outside (we just figured out its fall) = 20 delta T
Lets assume an 8ft tall wall of your home 20 ft long. = 160sq ft.
160 sq ft x 20 delta T x .033333333 = 168.42 Btuh of heat leaving that particular R19 wall in an hour.
160 sq ft x 20 delta T x .0769230769 = 246.15 Btuh of heat leaving that particular R13 wall in an hour.
There are 12,000 Btuh in one ton of Heating and Cooling so you can see this is a very small amount of energy savings considering the installation cost is about 45 – 60% more for R19 versus R13 to be applied in walls including lumber cost and reduced square footage. Let’s see where the real energy hog is.
New Fancy “Energy Efficient” window. With a .28 Uvalue (better than .30)
Area of window assume 3×5 and you have 4 in the room – 60 sq ft x 20 delta T x .28 = 336btuh of heat leaving the room.
Subtract the window area from your wall area (we assume you will CUT out a hole in the wall to place the windows) 160sq ft of wall minus the 60sq ft of windows.
100sq ft x 20 delta T x .0333333333 = 66.66 Btuh in the R19 wall and 336 btuh from the windows of that wall totaling 402.66 btuh on our R19 wall.
100sq ft x 20 delta T x .0769230769 = 153.66 btuh in the R13 wall and 336 btuh from the windows of that wall totaling 489.84 buth on our R13 wall.
As you can see the windows made the heat gain in that room go up by about double. I guess you could say the most efficient home would be one without any windows. The best design will have properly placed windows with proper passive solar shading that allows sunlight in the wintertime and reduces sunlight in the summertime as direct contact with sunlight is a whole other math lesson.
Congratulations! You just performed your first load calculation. Now rinse and repeat. A typical 2000 sq ft house has about 4000 of these calculations.
Spray Foam Insulation Comparison Chart
|Open Cell||Closed Cell|
|Spray In Insulation and Air Barrier Material|
|Able to deflect water and reject bulk water|
|Able to accommodate seasonal shifting|
|Able to accommodate seasonal shifting|
|R-Value (at 1")*||3.7||6|
|Blowing Agent||Water||Chemical, Water|