When placing de-icing cables on a roof which has leaf guards on the rain gutters the layout of the cables need to be modified from traditional installations because the small holes in the leaf guards freeze over very quickly.
Best practice for standard cable installation is to have the cables loop down over the edge of the roof down to the bottom of the rain gutter, where they will meet the same cable coming back along the bottom of the rain gutter to the downspout. When you have leaf guards you cannot get down into the rain gutter with the loops and you need the wire to cover more of the leaf guard to open more paths for water to go down. Essentially you need to come off of the roof onto the middle of the leaf guard, along the leaf guard a few inches, then back up on the roof – and then as usual back along the bottom of the gutter and down the downspout, out the end and loop the end of the wire back up into the downspout just to protect it.
BUYING THE RIGHT LENGTH WIRE
Study the layout instructions before choosing the length of wire to buy. De-icing wire cannot be cut to length or crossed over themselves. Yes you have to make a guess, make a rough layout, then finalize the attachments so as to use the full length of wire efficiently.
HOW TO PLUG THE DE-ICING CABLE INTO ELECTRICITY
Manufacturers recommend not using extension cords for two reasons: too long an extension cord can restrict the amount of electricity that will reach the de-icing line; and the joint between the extension cord and the de-icing cable must not get wet from dripping water. If you cannot install an outdoor electrical outlet box protected under the soffits, then attach the connection point between the two wires under the soffits with both wires looping down from the joint to cause any water to drip away from the joint, not into the joint. The electrical box should be installed near the downspout, not on the other end of the roof.
Even with an outdoor electrical box installed, the de-icing connection wire should loop down lower than the box and rise up to the box to be plugged in. Do not allow an electrical wire to be the drip path for water to get into the box.
PREPAIR THE LEAF GUARD
You will need to loosen the leaf guard grill enough to be able to run the wire inside the bottom of the gutter for the full length of the gutter and down and out the downspout before doing your rough layout of the wire.
LAYING OUT THE DE-ICING WIRE
Do a rough layout of the deicing wire starting from the electrical connection near the downspout using a minimum of attachments because you will probably need to adjust their position later.
1- Loop up onto the roof as indicated in the manufacturers instructions. The distance to go up on the roof should be a few inches beyond the house wall so the layout will be different for houses with larger soffit overhangs. (Follow this link to see details on how Ice Dams are created.) You may want wires closer together or higher up the roof in areas where excessive ice has formed in previous years.
2- Loop down off of the roof and down over the leaf guard, running straight along the middle of the guard several inches before returning to the roof for the next loop. This will thaw out more water passages into the rain gutter than if you just touch the leaf guard and return to the roof. (Installations without leaf guards drop to the bottom of the rain gutter and right back up, leaf guards need to receive more heat.)
This should remain loose for the moment to allow for getting inside the gutter with the wire in the next step.
3- At the other edge of the roof cut a hole in the edge of the leaf guard to allow the cable to drop inside the rain gutter and then run the cable relatively flat on the bottom of the gutter all the way across the roof to the downspout.
4- Feed the wire down the downspout and out the end about 4”, then loop the end back into the downspout just to protect it, leaving the loop just on the edge of the exit point. Some people use a tie-wrap to keep the cable from coming out, but do not bend the cable tightly. You may need to adjust the roof loops to have the end of the de-icing cable ending at the right point.
The de-icing cable should never cross over itself as it will overheat, so you cannot just stuff a lot of extra wire back into the downspout or the along the rain gutter and you cannot cut a de-icing cable.
Where you stop the cable, ice will form, so don’t stop inside the downspout.
5- Follow the wire back up from the end to place it neatly in the bottom of the rain gutter. If you are using an automatic control system with a sensor wire, install it now on the roof and inside the gutter as per manufacturer's instructions before re-installing the leaf guards. (see automatic controls below)
6- Re-install the leaf guard.
7- Now re-adjust all the roof loops roughly before fixing them into position, attached to the roof and to the leaf guard.
If conditions start to create ice in on the roof, the deicing cable will not remove the ice, but will create a free flowing drainage path for the water dammed up by the ice to flow down and over the edge of the roof, through the leaf guard, along the floor of the rain gutter and out onto the ground below.
If you want to use automatic controls rather than plugging and unplugging the system when you think about it, use ones designed for de-icing cables – usually sold right next to where you bought the cables, or at least controls like timers that are properly rated for the amperage of your cable. This is outdoor electricity and must have GFI circuit protection.
Automatic controls range from simple on/off timers, to ones with various sensors. My preferred, made by the cable companies themselves, is one that senses both temperature and water. This means it does not go on when it is raining and there is no chance of freezing, and when it is freezing cold, it will not go on if there is no water collecting. If there is no water under the snow pack, you will get no ice, but if the attic heat or solar heat is melting the snow creating water that can now flow towards the edge of the roof where it will freeze, the cables will turn on to keep it flowing right out onto the ground. Ice dams may form, but the cables will drain them and avoid water backup into the attic. That really keeps the system always operational without using electricity when it is not needed.
If you haven’t clicked yet, click on this link to learn more about Ice Dams.