Insulating a house attic with spray polyurethane foam (SPF) insulation on the underside of the roof deck is the best way in almost all cases to insulate an attic. This is especially true if the air distribution system (duct system) is located in the house attic. The benefits an unvented attic with cathedralized foam insulation are numerous; however in an existing home this approach is expensive compared to traditional insulation. This article explains how to make informed decisions about how to convert a house attic from traditional insulation to an unvented attic with spray foam insulation.
Benefits of an unvented attic with spray foam insulation
We inform customers that if you want the best home performance that money can buy and your home has an air distribution system in the attic, then half pound foam is the way to go. Your house will be:
- More energy efficient – lower utility bills
- Noticeably less dusty
- Much quieter
- Have fewer insects
These benefits are realized when you eliminate the attic vents, spray the roof deck with foam and bring the HVAC system, including duct system, into the thermal pressure envelope. These measures have a very positive effect on the home if done in conjunction with other good building science practices.
Think about it for a moment, in a conventional attic the air handler and air distribution system are working in a dusty environment that can reach 130˚F. The duct work containing the air has a very low insulation value and it leaks. Also most house are very connected to this attic through duct leakage and envelope air leakage. In time insulating attics the traditional way with blown-in insulation at the bottom chord will be seen as an obsolete way of insulating attics.
What is spray polyurethane foam insulation?
Spray polyurethane foam (SPF) is a spray-applied plastic that forms a continuous insulation and air sealing barrier on walls and roofs. It is made by mixing and reacting unique liquid components at the job site to create foam. The liquids react very quickly when mixed, expanding on contact to create foam that insulates, seals gaps and forms an air barrier. In retrofit attic applications Advantage Home Performance sprays a low density foam with a density ranging from 0.4 to 0.5 pounds per cubic foot. This foam is also refered to as open cell spray foam.
What is the difference between half pound and two pound foam?
At Advantage Home Performance we spray both half pound foam (open cell) and two pound foam (closed cell). More often than not we are spraying open cell in attics areas and occasionally in exterior walls. We spray closed cell or two pound foam in areas that require a vapor retarder or in crawl space that require more durable foam.
The low density foams we spray on the underside of roof decks in attics is a 0.4 to 0.5 pound density. The structure of open-cell foam consists of tiny bubbles or cells that aren’t fully encapsulated–they are broken, torn, ripped, etc. Because they’re broken, air fills the open space inside the bubble, which results in a soft, spongy material. Since they trap air the R-value is 3.5 per inch. Open cell foams are lighter in density they cost less to spray in attic.
Closed cell or two pound foam differs in that every bubble or cell that makes up the foam is completely encapsulated and packed tightly together. The bubbles aren’t filled with air, but rather a gas that aids foam expansion and insulation properties. Approximately 2” of two pound foam can form a vapor retarder. The aged R-value of two pound foam is about R-6 per inch. This results are altogether harder, stronger material than open-cell foam, but also a product that is significantly more expensive.
Does spraying foam in attics have a proven track record?
Spraying foam on the underside of roof decks and eliminating roof vents in not a new trend. Advantage Home Performance has been spraying foam on the underside of roof sheathing in new construction and existing homes for close to 15 years. We have had great success. Many major home builders in Arizona are now insulating their new homes this way.
What is the cost of spray foam in an existing home?
Although spray foam has a lot of obvious advantages, low density open cell foam has one major disadvantage – its cost. Spray foam insulation is expensive. Low density spray foam costs four to five times more than cellulose insulation blown in at the bottom chord. In other words if it cost $1,800 to re-blow an attic on a 2,000 square foot home it could be as much at $7,500 to $8,500 to remove the existing insulation and spray foam. Some of the factors that impact price include R-value of the spray foam be it an R-22 versus an R-38, pitch of roof, accessibility, depth of existing insulation, etc.
How much foam insulation (R-value) is necessary?
The building code now requires an R-38 to an R-49 depending in what part of the state you are in. In many of our jobs today we now spray either an R-30 (8.5”) or R-38 (10.5”). Before the code staring requiring higher R-values we insulated many homes with 6” of foam insulation (R-22) and achieved great results. We achieved great results because we tightened up the building and brought the ductwork inside the thermal pressure envelope.
How does foam insulation affect indoor air quality?
Another concern about foam is the impact on indoor air quality. It is important to note that half pound foam has been used in homes that meet the standards of the American Lung Association Health House program. The American Lung Association’s Health House program states that a house should be “built tight and ventilated right.”
At Advantage Home Performance we are both a licensed HVAC contractor and energy auditor and we can help customers address these types of questions. We charge for the audit, but provide a fifty percent refund if you have us perform the work we quote.
See our suppliers video called Healthy Home: Spray Foam Home
Does foam insulation pose a fire hazard?
The spray foam we spray contains flame retardants and is designed to meet applicable building and fire code regulations when installed properly. The foam we install is a class 1 building material which meets all codes.
What heating & air conditioning issues should I be aware of?
Mechanical units in an unvented attic with cathedralized half pound foam insulation are required to be either sealed combustion furnaces or heat pumps. It is not permitted by code to have 80% efficient gas furnaces in an unvented attic with foam insulation. Gas furnaces must be 90% sealed combustion appliances. Other issues you should be concerned about are combustion safety, room pressurization, building air tightness and to a lesser extent oversizing. We can assist you with these issues in our home evaluation.
Start with a whole home evaluation
You need to determine if your house is a good candidate for an unvented attic with spray foam insulation. Some of the issues to consider are building airtightness level, types of mechanical equipment, combustion safety, HVAC unit size, attic accessibility, …. Ideally you have someone inspect your home who possesses in-depth knowledge of building science and HVAC systems.
Advantage Home Performance is both a licensed HVAC contractor and we have BPI certified auditors on staff. We can provide either a free visual inspection or a comprehensive audit that we charge for, so you can make informed choices regarding your existing home and foam insulation. See our article called The Evaluation Process to learn more about comprehensive audits.
Is insulation removal necessary?
Yes! According to the “Guidance on best Practices for the Installation of Spray Polyurethane Foam” existing attic insulation needs to be removed. Here at Advantage Home Performance, we always remove the existing attic insulation prior to spraying the foam. It is the only way we can ensure the job is done properly from an air sealing perspective. Insulation removal also helps prevent odors from lingering in the attic.
Other benefits include home’s resale value and installer safety. A house with a foamed attic and insulation on the bottom chord is compromised. Eventually home inspectors will require that the insulation at the bottom chord be removed because this detail is not to industry standards. Insulation removal reduces the chance of someone putting their foot through your ceiling. Our crews have a much safer environment to work in when they can see the framing.
House preparation prior to foam installation
Preparing a house for foam insulation is a crucial step in the process. We go to great lengths to protect your property from spray foam overspray. In the photos below you can see how we covered cars and cabinets near attic accesses with plastic. This includes respect for your air distribution system in the attic a system that can be easily trampled during a foam insulation job.
Ventilation during & after application of SPF in attics
We go to great lengths to make sure that foam odors don’t migrate from the attic into the house while we spray the foam. With our fans we place the attic under negative pressure, so the flow of air is from the house to the attic and then to the outdoors. We also use our ventilation fans to evacuate residual vapors from the attic. Having said this, we still recommend that homeowners vacate their homes during the time we are spraying and return twenty-four hours after foam has been sprayed.
Spray foam industry problem
Our foam suppliers tell us biggest problem they have on retrofit spray foam job is having untrained applicators from mediocre insulation companys spray off ratio foam which means the chemicals don’t fully react and cause outgassing for an extended period of time. These incidents can be a real fiasco as far as the homeowner is concerned. Our foam applicators all have at least ten years of experience spraying foam.
Other problems result from the fact that the estimator did not know how to evaluate a house as a system and anticipate potential problems. Spray foam insulation will make homes tighter and there can be unintended consequences with combustion appliances and house odors starting to linger. Other potential problems are foam overspray, crushed duct work, etc.
Do your research – retrofit spray foam jobs are complicated
Retrofit spray foam jobs are much more complicated than traditional insulation jobs for a variety of reasons. We encourage all home owners to do there research prior to starting a job. Here is an excellent link for homeowners who want independent information: https://spraypolyurethane.org/Main-Menu-Category/Consumers
The next best thing you can do is be selective when choosing a spray foam contractor. Hire a knowledgeable and conscientious spray foam contractor who has a good reputation. He or she should have an in-depth knowledge of heating and air condition systems and building science. It will most likely cost more to have a knowledgeable professional do the job, but it is definitely worth the cost.
Why Advantage Home Performance?
Advantage Home Performance has been spraying foam insulation for over fifteen years. All of our spray foam technicians have over ten years experience spraying foam. We bring the auditing and HVAC experience to help you understand if your house is a good candidate for a retrofit foam insulation job.
The other main difference between Advantage Home Performance and most insulation companies is that we treat insulation like and integral system and not a commodity. We possess the values and building science knowledge that distinguishes us from most contracting companies. Please take a moment and watch our video, “The Company Culture Difference”.
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