Conversations with those new to SIPs inevitably turn to concerns and questions on how to run electrical through structural insulated panels. Most assume that the solid core of a SIP thwarts the efforts of your electrician to efficiently run wires through walls and roof. In actuality, with a bit of preplanning and knowledgeable SIP installers, Sparky can get wires from A to B with minimal effort.
As a standard, most panel manufacturers have predetermined the location of wire chases that meet common requirements for wiring a building. For instance, if electrical outlets are to be placed at 16” off the finished floor, most manufacturers will place a horizontal chase at that height in all wall panels. Likewise, as electrical outlets are required above kitchen counters, it’s logical to place an additional horizontal chase in the panel at 42”-44” above the floor. Some manufacturers place an upper horizontal chase at switch height. However, my experience has shown that 99% of all switches are next to doors so I recommend a vertical chase 6” from the door edge. If the SIP designer doesn’t know which way the door swings it’s not unreasonable to place a vertical chase on either side of the door at 6” off the rough opening. This vertical chase will allow the electrician to pull wire up to the switch box and continue on to an outside light or even up to an upper floor system or beyond.
The SIP manufacturing process uses predetermined box locations to design their layout of standard chases. Many will place a vertical chase in every panel for a four foot wide panel system or every four to eight feet if it’s a jumbo panel. Hence, if you allow the manufacturer to dictate the chase layout you may have a whole lot of chases that never get used. What’s wrong with that? Now you have to seal a lot of holes in your wall system.
I want my building envelope to be as airtight as possible so my approach uses a little preplanning to specify both vertical and horizontal chases only where they’re necessary. If plans change and an additional path is required there are simple methods that allow site chases to be installed in the field. My ideal factory-installed chase layout will include a vertical chase at all known switch boxes. Add to that a horizontal chase at 42” above the floor for panels in the kitchen area, and don’t forget to look for counters in other areas such as laundry rooms. Finally, I’ll add vertical chases as needed to ensure access to any remote areas or locations that don’t have any better option.
What about plugs in exterior walls? I’ll simply have my trained SIP installers site drill the plate, mark the deck for location, bore up from the bottom of the panel with a 1 ½ “ ship augers bit to a height of about 16” and then mark the panel. This simple prep will show the electrician exactly where he has access into the wall and avoids having him drill through the plate – a tough exercise when the SIP is already in place. With this procedure I keep my electrician happy and moving along with wiring at a formidable pace. The basement or crawlspace becomes the “horizontal chase” and we simply pull wire up 14” at each pre-drilled location. Have a concrete slab? This is one of the few times I’ll request a lower horizontal chase from the factory.
So when your client or builder starts talking about putting vertical chases in every panel, think like a molecule of air. Multiple pathways for air to move through your building envelope makes it more difficult to win the energy efficiency (airtightness) battle. If the paths are created by electrical chases you should plan to go back and fill or plug them all. My advice is to plan ahead with a complete electrical schematic and have chases installed only where you need them.