In the last few years, spray polyurethane foam (SPF) insulation has rapidly been gaining popularity as a premium insulation product for the construction market. Sprayed foam insulation is particularly useful because it is air impermeable; it bonds to and creates a seal with adjacent materials, and it insulates more effectively than other products.
In the past, you might not have encountered it too frequently, but, sprayed foam insulation has been used in buildings for more than 30 years. The basic chemistry for making foam has been known for more than 80 years.
Polyurethane foam is all around you: in your cars, in appliances, in foam cushions, and other household goods. Now it is becoming a common material used in buildings and the electrical industry needs to understand how to work with it and around it as part the everyday process of doing business.
Most electricians are, at least peripherally, aware of the need to air seal exterior walls, ceilings and floors over unconditioned space. Air leakage is a major cause of comfort complaints but it can also cause increased energy consumption, concealed condensation and related problems such as mold, corrosion and wood rot. Architects and builders striving for increased air tightness and energy efficiency often specify features like air-sealing electrical boxes, poly pan enclosures behind electrical boxes and airtight enclosures for pot lights/can lights to avoid these problems.
Foam insulation can greatly simplify these sorts of issues. With spray foam, the insulation itself provides the air seal, allowing other trades more flexibility in some of the products they choose and how they are installed.
Typically, rough-in electrical will be done before spray foam is applied with final connection of fixtures and other devices occurring after, however, it is often impossible to avoid running at least some circuits in insulated walls after the spray foam has been completed. Running circuits after spray foam application can be challenging, depending on what type of foam has been applied and how extensive the supplemental electrical work is.
In many cases, when foam is applied in wall, ceiling and floor cavities the type of foam you will encounter is Low Density Spray Foam Insulation. This type of foam is often called “half pound density” or “open cell” or even “Icynene foam” since Icynene was the manufacturer who first pioneered its use. It has the softness and consistency of angel food cake and can be easily cut to allow wiring to be tucked in. A pocket knife or even a credit card can be all that’s needed to get the job done. Minimize the damage to the foam and practically no repair work will be necessary. As long as you do not fully penetrate the foam (e.g. by drilling holes directly from the interior to the exterior surface of the foam) you will not compromise the air sealing it provides.
In other cases, particularly on the outside of the framing, you may encounter a tougher/denser/ harder type of spray foam referred to as Medium Density spray foam. Sometimes it is called “two pound density” or “closed cell” foam. It is much more firm, similar in strength to extruded polystyrene foam board you get at the lumber yard. The key difference is that its closed cell structure and adhesive properties are frequently chosen to provide a continuous vapor barrier as well as an air barrier. If you damage and do not repair this type of foam, an inspector may require repairs to the foam before construction can proceed.
In the case of either type of foam, if you remove large sections of foam, it will have to be repaired/replaced—minimize damage and you will minimize the need for repairs. If you are working around foam, it’s a good idea to contact the foam installer for recommendations and “spray foam kit or canned foam” products that are compatible with the material (s)he installed. Remember, when you apply even a small quantity of kit foam, that foam is produced by a reactive chemical process. Wear protective gloves, glasses and clothing and follow manufacturer recommendations regarding ventilation and/or breathing protection to avoid having that reaction take place on your skin or in your lungs.
Tips for working with spray foam
Spray foam can produce amazing results from a thermal performance and from the perspective of avoiding common issues related to air sealing and moisture control. But it can also produce surprises if you do not take steps to avoid them. Follow these tips to minimize problems with your electrical work.
At the Rough-in Stage
- Ensure all wiring is pulled tight and tacked at least every 24” or so to minimize displacement as the foam expands. SPF will also produce heat as it expands. NEMA-approved wiring is compatible however it may be necessary to run speaker wiring, network cabling and other services after foam is applied to avoid problems with unrated wiring.
- Mask the front of all electrical boxes, panels and equipment to avoid foam migration into unwanted areas.
- Use “air sealing” electrical boxes if available to minimize the amount of foam migrating into the boxes from the back and sides.
- Use can light enclosures that are compatible with spray foam and that do not rely on air movement through the enclosure for cooling/thermal protection.
- Though sprayed foam has only one quarter of the flame spread of wood products, it is still considered combustible. Follow all codes and manufacturer’s recommendations for separating heat-producing equipment and appliances from spray foam. Gypsum drywall and/or an air space may be recommended.
- Follow normal de-rating procedures for wiring heavy loads in well insulated assemblies. (Low Density spray foam insulation has an R-value that is comparable to other insulation types. Medium Density foam insulation is comparable to board stock products.)
- Do not do any wiring while spray foam insulation is being sprayed. A safe practice is to avoid working in the area while spraying is taking place and for a period of time up to 24 hours thereafter as recommended by the spray foam manufacturer.
At the Finishing Stage
- Remove any foam that has been over-sprayed on equipment and or into electrical boxes.
- If additional circuits/electrical are required run wiring on a path that minimizes the distance through foam—go through interior walls and floors to get to exterior walls and ceilings.
- Try to avoid penetrating supplemental wiring through foam. Supplemental air sealing may be required if holes are drilled through finished foam directly from interior to the exterior.
- Patch / repair spray foam with compatible products. (A low density spray foam should be repaired with a low density kit foam. A medium density spray foam should be repaired with a medium density kit spray foam.