People are extremely interested in spray polyurethane foam insulation (SPF). Most everyone realizes it to be the best insulation on the market but do not understand how it works, the two different types, which application is best and why.
There are two basic formulations of SPF-Open Cell (OC) and Closed Cell (CC). This is where most confusion seems to be. Both products, when installed correctly, create a complete thermal envelope; basically a seamless barrier around the exterior walls and roof line eliminating air flow through the structure. Sealing off or eliminating ridge, soffit and gable vents and applying SPF to the bottom side of the roof deck keeps heat from accumulating in the attic. SPF, in fact, is proven to reduce attic temps as much as 50 degrees on the hottest and most humid of days. Traditional (old school) ventilated attics are designed poorly so the end result only introduces unwanted heat and moisture into the attic. This constant draft of air creates a vacuum (chimney effect) drawing the costly conditioned air from the occupied portion of the home-through the ceiling-creating drafts around windows, doors, light sockets, etc. This intrusion of outside air/moisture/dust and pollens must be filtered/heated/cooled and dehumidified-thus drastically increasing utility costs. To complete the sealed envelope one must also seal the walls including all cracks and seams from windows/doors/top and bottom plates of walls, etc. The overall objective should always be to seal the structure as tight as possible and keep heating and cooling cost as low as possible.
The never ending question is always: Do we use open or closed cell SPF? The answer is not always the same. While both do a remarkable job in achieving overall efficiency performance, closed cell certainly offers advantages that open cell does not. Closed cell is an approved and recognized vapor retarder while open cell is not. This simply means open cell (perm rating 12%) will absorb and hold moisture while closed cell (perm rating 1%) will not. Much like traditional insulators such as cellulose/fiberglass/rock wool, etc., open cell SPF can contribute to mold growth inside wall cavities and reduced R-value over time. Closed cell SPF is the only FEMA approved product for below grade and flood zones for a reason. If it gets wet it does not have to be replaced as it will not absorb water. Open cell is not FEMA approved.
Closed cell also offers additional structural integrity. Independent case studies have proven close cell to improve racking (movement) strength by as much as 300%-will eliminate uplift inside the attic thus resulting in less-if any-structural damage in high winds. Open cell can hold no claim to these benefits.
In most cases open cell SPF will require an ignition or thermal barrier be installed over the top in attics and crawl space if the most recent code changes have been adopted. Closed cell usually does not require this step unless the area is to be “occupied” (used or lived in). NO SPF is allowed to be left without an approved thermal barrier if left exposed to occupied space.
In conclusion-both open cell and closed cell are wonderful insulators but do have distinguishable differences. Code requirements differ for each in regards to required ignition and or thermal barriers. When comparing prices both will basically be the same if the code requirements are the same for each jurisdiction. Before choosing which is best for your application consult with your local certified applicator and code official to insure everyone involved is up to speed on current requirements for plastic installations and then-based on requirements-you can clearly define which is best for your budget and silent comfort. Both types SPF are non-fibrous materials and will contribute significantly to improved IAQ (Indoor Air Quality) reducing dust up to 70%.
We are properly trained and certified and proud to offer both open and closed cell. We feel we have a moral and ethical responsibility to explain the products to the end user. At the end of the day we proudly install both after first insuring the end user understands the differences. Either way you will be not only be decreasing your utility cost, you will also be doing something positive for the environment. The less utilities used, the less fossil fuels burned, so the carbon footprint of your home or business will have less impact on the environment (for life). There is nothing “greener” to be done for benefitting the next generations.
Specialty Spray Foam is committed to today’s building science. We participate in numerous continuing education seminars and offer group training for home owners, code officials, architects and builders. We welcome your questions and offer free consultation and cost proposals.