According to Green Building Advisor.com, “spray polyurethane foam is better than any other type of insulation at reducing air leakage.” That's one of the biggest reasons that spray foam insulation is becoming one of the most popular insulation options in North America. We’ll talk about the two types of spray foam insulation-- open cell spray foam insulation and closed cell spray foam insulation. We'll also go over rigid foam insulation in today’s mini lesson. But, first, let me define “off gassing,” our pro term for this week.
Off gassing is the release of a chemical, especially a harmful one, in the form of a gas. It’s a term is that is most often used in reference to indoor air quality. Off gassing refers to the slow release of VOCs, volatile organic chemicals. "Volatile" means that the chemicals can easily evaporate or get into the air, at room temperature. "Organic" means the chemicals are carbon based, like carbon monoxide.
Off gassing can be encountered during new construction, but we also encounter it in new cars. You know that new car smell that most of us love so much? Well, that smell is off gassing. Off gassing may not cause any health problems at all, or it cause minor eye and respiratory irritation, or dizziness. In the worst case scenarios, off gassing might cause major breathing, or chronic health problems. The best thing to do is to avoid off gassing by choosing construction materials and products that have low, or no, VOCs, or to keep your distance from materials while they off gas.
Alright, let’s move on to today’s mini lesson. I’ll start by talking about spray foam insulation.
Spray foam insulation, also called spray polyurethane foam, is a heat-activated polymer that is sprayed in place. The foam is made by mixing two liquids onsite, using special equipment. Usually the liquid chemicals are housed separately in a truck, or trailer (chemicals are housed separately in portable tanks for smaller jobs). Then the chemicals are mixed together.
A chemical reaction takes place as soon as the two liquids are combined. A heated hose is then used to spray the mixture onto whatever surfaces need to be insulated. The mixture turns to foam, which expands, and eventually hardens in place.
There are the two kinds of spray-foam insulation— open cell foam and closed cell foam.
Open-cell spray foam, also know as half pound foam, is the lighter and less dense than closed cell. Open cell foam has a spongy consistency once cured. Open cell is less expensive than closed cell foam. It’s about half the cost of closed cell foam, but open cell has a lower R value. The R value of open cell foam insulation is 3.6 per inch. Open-cell foam is permeable to moisture, but impermeable to air.
Ok, here’s a very important point about open cell foam…You should be very cautious when considering spraying open cell foam on the underside of roof sheathing. Some roof sheathing can get wet when open-cell foam is sprayed directly against the underside of the sheathing. This increases the risk of roof rot. Strongly consider using closed cell foam on the underside of roof sheathing, as opposed to using open cell foam.
Closed-cell foam, also called 2 pound foam, is denser than open cell foam. Closed cell foam is impermeable to air and also impermeable to moisture, so it can act as a water vapor barrier.
So remember, closed cell foam is impermeable to BOTH air and water. While open cell foam is impermeable to air, but is permeable to water.
The R value of of closed cell foam is 6.5 per inch and closed cell foam is typically twice as expensive as open cell. Because closed cell foam is so dense, it’s rock hard once cured. In fact, close cell insulation is so dense that it provides some degree of structural reinforcement for homes.
If using green building products is important to you, you may want to avoid closed cell foam because the blowing agent for closed cell foam has a significant global warming potential.
Although there are some major differences in open cell and closed cell insulation, the two types of spray foam insulation share some characteristics and challenges.
A great advantage of open cell or closed cell spray foam is that spray foam can alleviate air leakages better than most other insulation option. That is a major reason why spray foam is popular despite its relatively high cost. The foam can fill up gaps and small holes, so it acts as an air barrier AND as thermal insulation. It’s also resistant to insects and rodents.
Manufacturers of open and closed cell spray foam indicate specific temperature and humidity levels that are appropriate for proper installation. Sometimes installers don’t take the outside climate and humidity into consideration. For example, in cold climates, a vapor retarder layer over drywall may be required with open-cell foam. If these manufacturers instructions aren’t followed, the insulation might be compromised.
Another installation issue that you should be cautious of is installers spraying the foam before the chemical components are warm enough. Remember that the foam is a heat activated polymer, so not allowing the components to come up to temperature can adversely affect proper mixing and foam performance. When the two chemicals aren’t mixed well or are mixed in the wrong ratio or at the wrong temperature, cured foam has been known to shrink away from surfaces.
Other installation problems include installers not spraying to the specified thickness or missing gaps and holes that should be filled. Any of these problems reduce the foam’s R value.
Some people have reported adverse reactions to the vapors that can linger after the spray foam insulation is installed. The Environmental Protection Agency, or EPA, has warned that vapors and dust that are released during and after installation of spray foam can cause respiratory and breathing problems, including asthma, plus skin and eye irritation. The EPA says that when spray foam that is correctly applied and allowed to fully cure, it’s typically considered chemically inactive, and generally not harmful.
BUT, when the foam is installed under adverse temperature and humidity conditions, OR when the foam is not mixed properly or not allowed to cure completely, problems with off-gasing can occur. So ensure that your spray foam guys follow the manufacturers guidelines for installation. The EPA also suggests shutting off the HVAC system and making sure air ducts are sealed tightly before installation of spray foam.
You could ask your installers what brand of spray foam they’re installing and check for yourself what the manufacturer's website says climate recommendations for installation.
You might also want to casually drop some the knowledge that you’ve learned in this podcast when you are chatting with installers so they know that you are educated about the process. You don’t want to sound like a know-it-all or be overbearing, just be casual and kind, but let them know that you are an informed consumer. You could say something like:
"I know that health issue can arise if spray foam isn’t mixed well or cured long enough. You don’t anticipate any problems with my house, do you?" OR you could ask “Have you had any issues with the spray foam pulling away from surfaces because it wasn’t mixed well or cured properly?” That type of conversation let’s them know that you’re educated and concerned homeowner.
Be aware that compared to other insulation materials, spray foam can be easier and faster to install, but it is also easier to rush through. If you let installer know you have some knowledge of the process, they’ll probably be less likely to cut corners.
If installed correctly, spray foam insulation offers substantial energy savings. Properly installing spray foam, or any type of installation, can make the difference between safe and highly efficient insulation and insulation that performs poorly and causes health problems.
Make sure you get several bids from installers that have significant experience with spray foam insulation and who have verified references. And before issuing the final payment, have the insulation checked by someone outside the spray foam company— someone like a home energy rater, a building inspector, or maybe your HVAC designer or installer.
If you decide that you like the idea of spray foam insulation, but not the price, you might want to consider a method called flash and batt. That can be a cost-effective way to get some of the air sealing and R-value benefits of spray foam without the paying for a full spray foam insulation job.
What happens with the flash and batt method is a thin layer of closed-cell spray foam in sprayed and then fiberglass batts are installed in conjunction with the foam.
Another foam insulation option is rigid foam insulation.
Rigid foam insulation is an alternative to spray foam insulation. It’s less messy than spray foam and it can be installed in any temperature. Rigid foam insulation is sheathing that is installed on the exterior of the home. It provides a continuous layer of insulation, which reduces thermal bridging.
Rigid foam can be installed on the exterior of walls, foundations and roofs. Some rigid foam also includes a radiant barrier for even greater energy savings. Rigid foam insulation protects against condensation on the inside walls by keeping the interior of the wall warmer.
A major advantage of rigid foam insulation over spray foam insulation is that the rigid foam was made in a factory, under controlled conditions, so you won’t have mistakes with mixing and curing.
The R value of rigid foam insulation can vary considerably depending on the type of rigid foam you choose. There are 3 main types to choose from, EPS, XPS and Polyiso. Their R values range from 3.8 to 8.0 per inch.
Rigid foam is usually more time consuming to install. And it needs to be meticulously installed to limit gaps and air leaks. So, as you can imagine, hiring an installer with lots of experience is essential.
In new construction, there are two basic ways to install rigid foam.
1) the foam can be used as sheathing and attached directly to the wall studs, or 2)walls can be conventionally sheathed with OSB or plywood, THEN the foam can be installed on top of the wood sheathing.
The advantages of using rigid foam INSTEAD of traditional wood sheathing are that rigid foam is lighter weight, easier to cut and cheaper than OSB or plywood.
However, although rigid foam insulation is less expensive than traditional sheathing, you’ll have to invest in added bracing or structural reinforcement materials to go along with the foam sheathing. Bracing materials like metal strapping, shear panels and a few sheets of plywood or OSB around critical areas like corners.
Ok, well, hopefully you know a little more about foam insulation than you did a few minutes ago.
Let’s see how you do on this week’s quiz. In this week’s quiz, I’ll describe different types of insulation. You tell me whether I’m talking about open cell spray foam, closed cell spray foam or rigid foam insulation.
1. This type of foam insulation is rigid, in fact, it’s as hard as a rock when cured. It has an R value of 6.5 per inch, is air and moisture impermeable, and provides some structural integrity, but is not a very green choice because it’s blowing agent is said contribute to global warming.
What type of insulation am I describing?
The answer is closed cell spray foam insulation
2. This type of foam insulation has an R value of 3.6 per inch, which is about the same the R value as blown in cellulose insulation, which we talked about last week. This foam insulation is also called half pound insulation and it has a spongy consistency when cured. It’s impermeable to air, but permeable to moisture so it might cause moisture related rot if applied on the underside of roofs.
Which foam insulation am I describing here?
It’s open cell spray foam. Remember, be very caution if you decide to install the underside of your roof with open cell foam, your building inspector may allow it if you include extra precautions, but closed cell foam or rigid foam are better options for roofs.
3. This foam is made of two liquid components that must be mixed to the right ratio, heated onsite and installed under specific climate and humidity conditions in order for it to adhere to walls and cavities and to cure as it should. Off gassing may be an issue during and after installation.
What foam am I describing?
This statement is true for open cell AND closed cell spray foam insulation.
4. This insulation is made offsite, in a factory, so climate and humidity are not a factor during installation. This foam insulation is installed on the exterior of the home either in place of traditional sheathing or on the outside of traditional sheathing.
The answer here is rigid foam insulation.
That’s it for this week. I hope you learned as much as I did. If you like the show and think it would be helpful to someone building or remodeling a house, you can share it with them on Facebook or Twitter.
Please remember that the purpose of this podcast is simply to educate and inform. It is not a substitute for professional advice. The information that you hear is based the only on the opinions, research and experiences of my guests and myself. That information might be incomplete and it’s subject to change, so it may not apply to your project. In addition, building codes and requirements vary from region to region, so always consult a professional about specific recommendations for your home.
Thanks for joining me today. I hope you’ll come back next week for Build Your House Yourself University (BYHYU).
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