Spray foam insulation: tips for electrical professionals
Over the last few years, spray polyurethane foam (SPF) insulation has been gaining popularity as a premium insulation product for the construction market. SPF is particularly useful because it is air impermeable; it bonds and creates a seal with adjacent materials, and insulates more effectively than other products.
In the past, you might not have encountered it too frequently, but SPF has been used in buildings for more than 30 years; in fact, the basic chemistry for making this foam has been known for more than 80 years!
Polyurethane foam is all around you: in your car, 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 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 not only a major cause of comfort complaints but can also cause increased energy consumption, concealed condensation and related problems, such as mould, corrosion and wood rot. Architects and builders striving for increased airtightness and energy efficiency often specify features like air-sealing electrical boxes, polypan enclosures behind electrical boxes and airtight enclosures for potlights to avoid these problems.
SPF 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 subsequently installed.
Getting to know foam
Typically, rough-in electrical will be done before spray foam is applied, with the final connection of fixtures and other devices occurring afterward; 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 the type of foam that has been applied and the extent of the supplemental electrical work.
When foam is applied in wall, ceiling and floor cavities, the type you will typically encounter is Low-Density SPF. This type of foam is often referred to as half-pound density or open cell (maybe even Icynene foam). 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. So 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, also known as 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 vapour barrier as well as an air barrier. If you damage but do not repair this type of foam, an inspector may require repairs to it before construction can proceed.
In either case, minimize the damage and you minimize the need for repairs. Should you remove large sections of foam, they will have to be repaired/replaced. If you are working around foam, it’s a good idea to contact the foam installer for recommendations and a “kit or canned foam” product that is compatible with the material installed.
Remember, foam is produced by a reactive chemical process. When you apply even a small quantity of kit foam, be sure to wear protective gloves, glasses and clothing, and follow the manufacturer’s recommendations regarding ventilation and/or breathing protection to avoid having that chemical reaction occur on your skin... or in your lungs.
Spray foam does not only produce amazing thermal performance results, but can help the project avoid common issues related to air sealing and moisture control. Likewise, it can also produce unwanted surprises when you do not take steps to avoid them. Follow these tips to minimize problems with your electrical work.
At the rough-in stage
1. Ensure all wiring is pulled tight and tacked at least roughly every 24-in. to minimize displacement as the foam expands. SPF will also produce heat as it expands. NEMA-approved wiring is compatible, but it may be necessary to run speaker wiring, network cabling and other services after the foam is applied to avoid problems with unrated wiring.
2. Mask the front of all electrical boxes, panels and equipment to avoid foam migration into unwanted areas.
3. Use air sealing electrical boxes if available to minimize the amount of foam migrating into the boxes from the back and sides.
4. Use potlight enclosures that are compatible with spray foam and do not rely on air movement through the enclosure for cooling/thermal protection.
5. Even though SPF has only 1/4 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.
6. Follow normal de-rating procedures for wiring heavy loads in well-insulated assemblies. Low-Density SPF has an R-value that is comparable to other insulation types. Medium-Density SPF is comparable to board stock products.
7. Do not do any wiring while SPF is being sprayed. A safe practice is to avoid working in the area while spraying is taking place plus a period of up to 24 hours thereafter.
At the finishing stage
1. Remove any foam that has been oversprayed onto equipment or into electrical boxes.
2. If additional circuits/electrical are required, run wiring along a path that minimizes the distance through foam. Go through interior walls and floors to get to exterior walls and ceilings.
3. Try to avoid penetrating supplemental wiring through foam. Supplemental air sealing may be required if holes are drilled through finished foam directly from the interior to the exterior.
4. Patch/repair spray foam with compatible products e.g. a Low-Density SPF should be repaired with a Low-Density kit foam.
As spray foam insulation’s use within residential and commercial construction continues to increase, it makes sense to avail yourself of the resources and education offered by industry to better understand the products and their functionality, and how they work in conjunction with other building materials.
Through education and collaboration with subject matter experts in the insulation space, electricians, designers and other contractors during the design or build phase can better grasp the various types of SPF available and how they are used in the building envelope.
About the Author, Paul Duffy
Paul Duffy is vice-president, Engineering, with Icynene. He has more than 20 years of building science and engineering experience, and he’s an active contributor to the Code changes within the United States and Canada. Paul is currently Chair of the Spray Foam Coalition and Chair of the SFC Research Committee for the American Chemistry Council – Center for the Polyurethanes Industry.