Removing Ice on Roofs

by Nate on June 17, 2011

each corner of the roof. (Do not put the electrical cables inside the drain — the drain pipe may contain inflammable gases). Run a loop around obstructions, such as skylights and ventilation hoods. If you can work safely near the edge of the roof, run a cable around the inside perimeter (Figure 2).

Figure 2 : ‘X’ Formation on Flat Roof

The cable will melt its way to the roof surface and keep drainage paths open. It will not penetrate the ice until it is warmer than -10°C and, of course, will not work if there is no electricity.

De-icers for cutting into ice

Pour a 6-mm thick by 75-mm wide (1/4 in.-deep by 3-in. wide) path of de-icer from the drain to each corner of the roof and circle obstacles such as ventilators and skylights. Use the same drainage pattern as you would for electrical cables. See Chemical De-icers for details on products. You may need to use a de-icer more than once to melt through to the roof and to keep drainage paths open.

Ice removal is not a good do-it-yourself project. But homeowners can shovel heavy snow off the top of the ice, which might keep the weight load under control.

Ice thickness and weight of ice can be reduced with de-icers such as urea or even wood ashes. Both are slow and work only in relatively mild weather. To ensure water run-off, create drainage paths as described above. Ashes must be directly on the ice, with no snow over or under the ashes, so they can trap the sun’s heat.

Chemical De-icers

Many de-icers don’t show their ingredients on the packaging. Others list ingredients without showing the relative importance of each.This is no help in deciding which de-icer is safe for a roof or better at cutting drainage paths or reducing ice weight.

In general, the least expensive, most effective de-icers are highly corrosive and should not be used on a roof. Urea, the least corrosive, is also the least effective. In between are several products that are a bit more expensive, still effective and reasonably low in corrosive action.

In general, larger rock-like products tend to cut through ice quickly. Finer, powder-like products tend to perforate the ice. This creates a honeycomb effect that makes the ice lighter. Liquid products are the most effective for detaching blocks of ice from the surface.


Salts containing oxidizing agents (these accelerate corrosion and rust and can deteriorate other roofing materials) such as:

NaCl (Sodium Chloride)
CaCl2 (Calcium Chloride)

Safer materials

CMA (calcium magnesium acetate)

The following are normally used as fertilizers:

KCl (Potassium chloride)
(NH4)2 SO4 (Ammonium Sulfate)

Life Safety

Ice is slippery and in emergency conditions medical help may not even be able to get to you. Not only can you slip, but ladders can slip. Removing ice from the edge of a sloped roof can release large fields of ice higher up that can slide down on top of you. During the 1998 ice storm, more than one person died from icicles falling from above when they were simply standing in the driveway below.

Double and triple your safety precautions, or stay away from the roof. Rope off areas and access doors where overhead ice is heavy or slides made occur (Figure 3). Never work alone. Always have someone on the ground to ensure that what you throw off the roof is landing safely.

Figure 3 : Rope off areas where overhead ice is heavy or slides may occcur.

On a sloped roof, always tie the ladder down and have a safety rope over the top of the roof secured on the other side.The safety rope should be attached to a full safety harness, like mountain climbers use — it is not there just in case you slip — it is there because you will slip and more than once.

Special ice cleats are available in shoe repair and hardware stores for attaching to shoes and boots, making them much like golf shoes. These are good for not slipping, but are not good for shingles. Walking on icecovered sloped roofs is best left to professionals with professional equipment.

Detaching ice blocks from surface

Liquid de-icers (e.g. Clear Away) were efficient at melting the bond between blocks of ice and roof membranes.

Methyl alcohol worked as well.

Techniques with moderate success

Cutting drainage paths with hot water

This is actually rather effective if you can get hot water very close to the ice (50 to 100 cm — about 2 ft.) and prevent the hose and nozzle from freezing (Figure 4).

Figure 4 : Hot water being sprayed from dormer window.

The drain must first be freed of ice, so that the water can drain away. However, this means you will be undercutting the mass of ice above you, and this ice may come down.

The only safe way to do this job is to cut thin slices off the

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