Updated: May 18
You’ve made all the calculations, bought the heat trace cable and the roof clips, and you have the heat trace products experts at HeatCable.com on speed-dial just in case. The sun is shining, the roof is dry, and you’re ready to go. Let’s do this!
Prep Your Roof
Just like when you paint a room, it's best not to skimp on the prep work. It will take some extra time, but your result will be a clean and professional-looking project. Carefully unravel your heat trace cable, lay it out straight and double-check the length to ensure you have the amount you need. Next, borrow a piece of chunky sidewalk chalk from your kid and head up to the roof. Using a tape measure, start at an interior corner and make a chalk mark every 18 inches at the roof edge for the cable clips. Once you get to the outer edge, an easy way to mark the top of your zig-zag is to make a triangle with your tape measure as we showed you in Part I. Place it on the roof just like you plan to lay out the heat trace cable, putting your chalk mark at the top. Working back the way you came, now you can mark the roof at the top at 18-inch intervals just like you did on the bottom. Stretch your tape measure to about six feet up from the roof edge for your valleys. Make chalk marks on each side of the valley at 20 inches, 40 inches, and 60 inches. You will use your clips at those points to anchor the heat cable going up and back down the valley.
Attach the Clips
Whether made out of metal, asphalt, or any other material, every roof can accommodate heat trace cable with the proper clips. Since asphalt shingles represent the most common residential roofing materials, we want to show you how to attach the cable clips to this type of roof. You'll need some essential tools:
Perforated metal cable clips (we recommend the clips sold on HeatCable.com)
An extra-thin flat pry bar
A caulking gun
A high-quality glue like Chem Link's M-1 Universal Adhesive & Sealant
Your roof has three main layers: the shingle, the ice and water shield, and the drip edge. The metal roof cable clip has a flat, perforated surface with a drop-down tab in the middle. For the roof edge clip, begin by pulling the drop-down tab to where it’s at a 90 degree angle. Using the caulking gun, cover the area on top of the clip around the drop-down tab with a strip of glue about a quarter-inch to a half-inch in diameter. Next, apply glue to the side of the tab facing the roof and slide the clip under the shingle, pressing firmly to distribute the adhesive. If your roof shingle doesn't lift enough at the edge to slide the clip underneath, use the flat pry bar to gently lift the shingle and make room. The glue on the flat part of the clip works to attach it to the underside of the shingle and the bottom to the surface underneath via the perforations. The glue on the tab will attach the clip to your roof’s drip edge. Gluing the tab to the drip edge is a critical step because the glue on the flat side of the clip won't keep the fastener firmly in place. While the clip will seal itself to the shingle on top, it won’t attach on the bottom because the ice and water shield has a grainy surface that doesn't take adhesive. Over time, the pull from the cable will raise the shingle and clip away from the roof, rendering that area more susceptible to leaks underneath. By sealing the drop-down tab to the drip edge and the flat part to the shingle, you ensure that the clip and cable will remain firmly in place. With your tab down, the clasp also will extend slightly over the roof edge, creating a direct path for melting snow and ice to flow into the gutter. You’ll use a similar process to attach the cable clips in the roof field. Those shingles will need a little more effort because they are already sealed in place with glue or tar. Again, slide the pry bar under the shingle and work it back and forth while keeping it flat against the roof surface. You should be able to create an opening large enough for the clip to slide in fairly easily. Be careful not to lift upward with the pry bar, as that will tear the shingle and damage your roof. Unlike at the roof edge, you want to leave the drop-down tab in place. Spread a layer of your adhesive over the entire flat surface of the clip and then slide it under the shingle where you made your chalk mark. It's a good idea to leave about half an inch of the surface area exposed to give you plenty of room to bend the flange around the cable without cutting into the asphalt on top. With the clip under the shingle, press down on the area to ensure the adhesive spreads all around the clip and the opening. The process is roughly the same for attaching the clips on both sides of the roof valleys, or you can opt for a smaller, grip-type hook that latches onto the edge of the shingle.
Lay the Cable
Beginning at the point farthest from the downspout, thread your constant wattage or self-regulating cable through the gutter in the direction of the spout. It's critical to insert the line under the gutter spikes to ensure maximum efficiency in melting the gutter ice. Another good idea is to have a buddy with you to pull gently on the cable as you lead it into the gutter. That way, you minimize tension in the cable and the risk of damaging it on any sharp edges of the gutter. Once your wire reaches the opposite end of the roof, pull it down to the end of the spout. Draw any excess cable back along the gutter to where you started. It's time for your zig-zags. There's usually space between the point where the roof zig-zag pattern starts and the end of the gutter. To ensure that the small area does not freeze, thread the cable to the end and loop it back in the gutter to the chalk mark on the roof where your first zig-zag begins. Since that small part of your roof gutter will have two parts of the heat trace wire side-by-side, use a cable separator to keep them from overlapping and shorting out or overheating. These little gadgets will come in handy for doing your valleys as well, where you will have two lines of cable coming back to the roof edge at the same point. Next, install your cable along the roof clips until it reaches the downspout. At that point, you should have just enough line to reach your outlet. If you calculated for valleys, attach the cable to the clips up to the valley. Now take the other end of your heat trace cable (the end with the plug), leave enough to reach the outlet, and begin attaching it to your roof clips from that side. This seems a little counter-intuitive, but when you come to the valley from that end, you'll see why it's critical to do it this way. If you have too much cable or not enough, your system's buffer zone will be in the valley. You're done! Remember, if you run into any issues, your pros at HeatCable.com are only a click or a phone call away at (801) 896-8960. Check out more of our How-To videos like this one if you'd like a visual of anything we covered in this two-part series.