Flat roof ice dam leak stoppage, prevention & protection:

This article illustrates the successful installation on a nearly-flat EPDM roof to stop a winter leakk into the building. The photographs and text explain the steps of observing a building leak, tracing the leak to outdoors to melting snow and ice on a roof, and the installation of a roof/gutter de-icing kit to stop the leak.

Special attention and some creative steps were needed to secure the de-icing cable on a nearly-flat surface without causing damage to the roof, and extra details were needed to be sure that water could find its way completely off of the roof surface.

Stop an Ice Dam Leak Using Heat Tapes & De-Icing Cables on Flat, Low-Slope or EPDM Roofs

These photos and comments describe the diagnosis and cure of roof ice dam leakage occurring on a low-slope EPDM-covered roof in a New York Home. Most likely the first notice you will see of a snow or ice related roof leak will be water dripping from a ceiling or a puddle on the floor. That's what we found at the home shown at left. Water was dripping out of a door frame at a passage between an older section of a home and a new addition.

[Click to enlarge any image]

The immediate steps to respond to this leak involved the following:

1. Control the water: Put down a drop cloth to keep water on the floor from passing further under walls and trim where it will increase the risk of mold contamination. (Above left).
2. Find the leak source: Inspect outside to see where the leak is probably originating and to decide what emergency steps can be taken there. Outside I saw an ice build up at the point of drainage of a low slope roof (above right). I suspected that an ice build-up was pushing melting snow on the roof surface up high enough that it was entering the wall-roof abutment over the top of flashing at that location. An alternative explanation that could not be explored until the roof surface was exposed was that there could be an actual perforation of the EPDM roof surface in the area of the leak or up-slope from it.

We all suspected that although the roofs of the addition walls and roof of this home were super-insulated - mostly - there were some voids or air leaks in the older lower flat roof that might be warming the under-side of the snow and allowing water to leak in to the building.

Accessing the lower roof by ladder we saw deep snow piled over the area that was leaking indoors. Using a push broom it was possible to sweep enough snow off of the roof drainage area to find melted ice and snow at the roof surface (above right).

This was the melt that was backing up enough to find its way over vertical sidewall flashing installed at the intersection of the second floor wall (the yellow wall in these photos) and the lower flat EPDM roof.

At below left you can see where it was easy to sweep off snow and where ice remained adhered to the flat roof surface.

All of the accumulated ice (and slush) were in the lowest portion of this roof in an area that had been constructed to drain off at the roof edge. This suggests that backup at the gutter and roof edge may have been sending water into the roof at its edge.

Using a heat tape to melt drainage passages through this area ought to stop the leakage.

In the photo at above right I'm pointing to ice and stains showing that water from this flat roof ice dam leak was passing behind the fascia board. It's possible that water was entering the roof structure right at the roof edge - in an area currently hidden by the ice dam that formed in the (debris-clogged) gutter, or we may have two leaks.

3. Stop the leak: no one was interested in tearing off siding nor clearing all of the snow off of the entire roof to pinpoint the exact point of water entry during the middle of cold winter and in deep snow.
   
   I decided to clear off as much loose snow as possible and to install a roof de-icing cable on the roof surface and into the gutters.
   
   By melting a passage off of the roof past that ice dam at the roof edge any snow melt on the roof could drain safely off of the roof without backing up to leak into the home.

A question is how do you place and secure de icing cables on a flat roof. More, how do you place and secure de-icing heat tapes on a flat roof when the roof has snow and ice on its surface? I swept off as much snow and ice as possible. That step alone stopped water from entering the building below, but without further measures the leaks might have resumed at the next snow fall had we not installed a de-icing cable.

The de icing cable was also run in the gutter atop the ice there so that we had multiple efforts to melt a drainage channel through the ice, stopping leaks both from water backing up the roof and leaks from water running between the gutter and the fascia.

As the day warmed and we were lucky to have some sun, the black EPDM absorbed enough heat to melt more of the remaining snow and ice cover but I'd have placed the heat tape as shown regardless of whether or not I could get down to the roof surface.

Watch out: read the roof heating cable instructions provided the manufacturer. Among the important advice you'll find there is the admonition that the heating cable should be plugged into a GFCI-protected electrical receptacle. Happily on this building a suitable outlet was close-by outdoors, and low on the building wall. That makes turning the heat tape on or off easy: just plug it in or un-plug it.

We routed the heating cable power line upwards behind a downspout to where the heating line was needed at the roof edge. This sloppy installation can be neatened up when the weather warms. Right now everyone just wanted to "get it working".

Watch out: even when a roof leak has been successfully stopped you may need to investigate building cavities that have been wet, removing wet insulation and removing mold contamination.

4. Prevent future ice dam leaks: The heat tape was placed in a series of parallel loops on the roof surface, concentrating the loops in the lowest point from which the roof should drain.
   
   The intent was both to assure drainage through the present ice dam and to keep drainage passages open along the roof edge should there be more snowfall.

Watch out: buy the correct kind of heating tape or cable. Shown at left is a roof heating cable intended for outdoor use. While the braided metal heat tape or cable at below right in the photo below is really appealing and can be made to any length needed, this is not the right stuff. The braided metal cable heat tape and its connectors are intended for use only indoors in a dry location and are designed to prevent pipes from freezing.

Watch out: most outdoor de-icing cables or heat tapes intended for use on a roof should not be criss-crossed over themselves.

The manufacturer provides several devices such as soft aluminum hooks that can be used to keep the parallel cables from touching one another.

I used a mix of bricks, aluminum hooks, and even a couple of weights hung over the outermost loops of de-icer cable all intended to encourage the cable to melt its way down through the ice dam and to assure positive drainage off of the roof.

At above left you can see my aluminum hooks (provided by the manufacturer) keeping the heat tape loops from touching and you can see that the de-icer cable is indeed melting its way through the ice dam at the roof edge.

At above in my second photo you can see a close-up of how effectively the heating cable has melted drainage passages through the roof ice.

Watch out: do not use any heat tape securing method that risks punching a hole in the EPDM. And do not use weights (like my bricks in the photo above) if they may slide off of the roof and whack someone.

5. Monitor the heat tape system for proper operation: we checked the status of the roof over the next few weeks, taking note of how the de icing cables were performing when there was more snowfall and more freezing weather.

As you'll see above, during future snowfalls and freezing weather the de-icing cables had no trouble maintaining a drainage passage off of this nearly-flat rubber roof.

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Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

On 2019-03-11 - by (mod) -

When there's no snow or ice on your roof you could of course turn off the heating types.

However for many people who are not always at the building to turn tapes on and off as weather conditions change or who may forget to do so, it's pretty common to simply leave the heating tapes on until you're at the end of freezing weather or snow season. Actual wattage or electrical use of these devices is usually not very high.

On 2019-03-10 by Agnes Fangmeier

Is it necessary to leave heat tapes on at night when snow is no longer thawing - weather below 32 degrees? Or what is the proper way to use heat tapes?

On 2018-12-18 by Don

Will the actual heated de-icer cables, not the clips, damage a flat roof membrane?

Will de-icer cables cause damage to flat roof membrane if in direct contact?

On 2018-10-22 - by (mod) -

Tony

On a nearly flat roof where I needed some heating cables I simply place them in position on the roof and put little half bricks to wait them in place. Obviously on a membrane you don't want to punch holes or damaged the membrane with clips. I don't think that at he is or Hot Melt glue is a good idea because the cables themselves make it warm enough to soften that bonding agent but contact cement might be another option

On 2018-10-22 by Tony Henderson

How do I attach the cable to my low sloping roof,and I have no gutters or shingles on my low sloping roof

Question:

(Jan 9, 2015) Dee said:
Who do I call to xheck the wires on my roof

Reply:

A roofer who has experience with hooking up ice dam prevnting heating tapes or cables, an electrician, a handyman, a building contractor:

Watch out: accessing a roof edge from a ladder is always risky, especially in winter.

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• ROOF ICE DAM DIAGNOSIS

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