Part H · the register

Heat Cable at a Kirkwood Eave Is a Stopgap, Not a Repair

A heat cable can keep one eave open through a freeze, but it does not fix the roof or the attic above it. Here is what to check before you buy.

When snow sits on a Kirkwood roof through a cold week, the stretch that matters most is often the lowest two or three feet at the eave. Heat from the house leaks up into the attic, warms the underside of the deck, and melts the snow on the slope above. That meltwater runs down to the overhang, which sits outside the warm air, and freezes at the edge. The ice builds into a dam, and water backs up under the shingles where nothing stops it. This is ice damming. It shows up on the same Kirkwood houses winter after winter, usually on the shaded faces that hold snow longest. A heat cable is one answer homeowners reach for when a stain appears on the ceiling in January. It is worth understanding what the cable does and what it leaves alone before you order one.

What a heat cable does

A heat cable is a resistance wire, sold by length, that carries current to warm the surface around it. Installers usually run it in a zigzag along the eave, up the valley or gutter line if needed, and down through the gutter into the downspout so meltwater has a route to leave. A thermostat or sensor controls when it switches on. It keeps one channel open through a freeze, so water drains off the edge instead of pooling under the shingles for that season. That is useful, and for some houses it is the right short-term decision.

It does not change why the snow melted. Warm air that reaches the attic is still there, the insulation may still be leaking heat, and the soffit vents may still be blocked by old insulation pushed against the eave. The cable treats the symptom at the edge. The heat loss, the air moving into the attic through the top plates, the attic hatch, and the recessed lights continues whether or not the cable is switched on.

Check the attic before you buy cable

Go into the attic on a cold, clear morning and look at the underside of the deck near the eave. Frost on the nail tips or a dark, damp line along the sheathing means warm moist air is reaching the roof deck. Look at the soffit vents too. If insulation blocks them, air cannot move from the soffit up toward the ridge, and the deck stays warm in patches. Then check where the warm air enters: around the attic hatch, plumbing penetrations, the bathroom fan duct, and the chimney chase. Each of those is a path a cable at the eave will never reach.

Ask the roofer, or an energy auditor, to tell you which of those paths is open. Keys Roofing can look at the eave, the overhang width, the gutter type, and the vent layout, and write down what it sees with photographs and measurements. That written record is yours to keep. It will tell you whether a cable is only a stopgap for this house, or whether the attic needs work first, and in which order the two jobs should happen.

Where the cable will and will not reach

A heat cable covers only the eave you can reach with it. On a low pitch, a long plain eave, or a valley that carries snow down into one corner, a single run may not be enough. Ask where the installer plans to end each run and where the cable leaves the gutter. A common failure is a cable that stops at the eave and leaves the downspout unheated, so the water freezes inside the spout instead of at the edge, and the gutter overflows onto the same wall it was meant to protect.

Ask also how the cable is attached. Clips should be fastened to the gutter or to the fascia in a way that does not put fasteners through the shingles or into the wrong part of the trim. If the next roof replacement is a few years away, note where each clip sits so the crew that tears off the old shingles can work around it instead of prying up a run of cable with the roofing.

The power side

A heat cable draws current outdoors, in wet weather, on a roof edge. The circuit should be protected by a ground fault circuit interrupter, and any receptacle or connection should be rated for outdoor use. Ask who runs the new circuit and whether the city expects a permit for the electrical work. In Kirkwood, questions about permits for electrical work go to the city's building staff, and a permit desk can answer them before the work begins. Do not let the cable plug into an indoor outlet through an extension cord. That is the setup that creates the fire risk a homeowner was trying to avoid in the first place.

Timing for a Kirkwood winter

Install before the first hard freeze, not after the first ceiling stain. Freeze and thaw cycles in the St. Louis area can arrive early and then swing back and forth for weeks, so a dam can form during one warm afternoon followed by a night well below freezing. A cable still in the box on a Tuesday in January does not help the ceiling below. Late October and November are the practical window for planning. An electrician can look at the outlet route, the roofer can check the eave, and the cable can be tested before the first real snow arrives.

What to ask before you agree

• Where does the cable start and end, and does it run down into the downspout?
• Which circuit feeds it, and is that circuit protected by a ground fault circuit interrupter?
• Who fastens the clips, and where do the fasteners go?
• What will be checked in the attic before the cable is bought?
• Will the cable plan be written down, with a photograph of the eave before and after the work?

A roofer can answer most of those questions, but the attic work and the outlet work may belong to other trades. Get each answer in writing and keep the list in one place, so that every trade on the job knows which part of the eave and which part of the house it is responsible for.