Melting Snow Is An Annual Problem, But What Can Be Done About It?

Your roof doesn’t leak all summer long from the rain, but here it is in the winter and you have a leak.  Why is that?

A water leak from melting snow is caused by interior heat. Snow or ice on the roof is melted from underneath by heat from the interior. The water from this melting action is trapped and "dammed" by ice and snow above.

Water is also dammed on the roof gutters and downspouts. The water then takes the path of the least resistance and may travel up the roof and under the roof system, or sideways and through flashings, which were not designed for ponded water.

Question: Why doesn't it leak every snowfall?
Answer: In most cases the exterior temperature is warmed up by the sun and  is warmer than the roof deck; therefore, the water runs off from the top down and no "ice dam" is created.

Question: What can be done to correct today's leaks?
Answer:  If the interior heat cannot be eliminated, the short-term remedy is to create "water runoffs" through the ice and snow here is water discharge off the roof. Creating the runoff is extremely dangerous to the snow removal person and may unavoidably damage the roof system. Scraping, chopping and breaking of ice may cause shingles to break or become gouged. This unavoidable damage is a trade off and less severe than interior damage caused by "melt-off" penetrating the interior and damaging ceilings, walls, insulation, and creating potential electrical hazards.

Question: What can be done to avoid leaks in the future?
Answer:  The source of the problem is interior heat which warms the roof deck causing the melting of ice and snow from underneath. To stop the melting, one must lower the roof deck temperature below the exterior temperature.

This can be achieved by lowering interior temperatures by adjusting the thermostat setting, and/or increasing ceiling insulation so interior heat does not warm the deck, and/or increasing under deck ventilation to exhaust interior heat before it warms the deck.
Any one or a combination of these methods may be nessesary in order to keep the deck cool so melting does not occur. The deck must remain colder than the exterior, which may not be possible during extremely cold periods.

For these situations, special flashing systems, and "ice dam" protection membranes are installed to waterproof the roof and sidewalls. In some cases electric "heat tape" can be installed prior to snowfall to assure there is a water mitigation pathway.

• Leaks at skylights: Snow and ice can build up on a roof to a height that covers the "weep holes" of skylights. Internal condensation, which would normally escape through the "weep holes", is trapped and causes leaks.
  
  The temporary remedy is to remove the snow and ice around the skylight. The long-term solution is to raise the skylight above anticipated snow levels. Skylight leaks may also be caused when snow builds up above the height of the roof flashing. Again, the short and long-term remedy remains the same.
  
  Skylights may also leak during rain while ice and snow are still on the roof.  The source of this leak is the water running on top of the ice at a higher level than the roof surface and being forced in above the flashings or through skylight lenses.  Again, the short and long-term remedy remains the same.
  
  
• Leaks in cathedral ceilings:  With a cathedral ceiling it is easier for interior heat to warm the roof deck compared to roof decks with attic space and ventilation below. In addition, the common use of "recessed lighting" in cathedral ceilings creates both a heat source and heat pathway to the deck.
  
  The short- term remedy is to turn off recessed lighting and severely lower interior temperatures so the roof deck re-freezes. The long-term solution is to construct a "cold roof deck" and/or install waterproofing "ice dam" protection membrane over the entire roof. The long-term effect of "ice dam" protection on an entire roof, which may impede normal ventilation, is not yet determined.
  
  
  
• Leaks at ridge vents:  Heavy accumulation of ice and snow may cover over and cause leaks at ridge vents. These leaks usually self-correct since the ice melts off first from the ridge vent.
  
  The short-term remedy is to create a water migration pathway. The long term solution is to raise the level of the ridge vent or if the existing vent is metal, install a newer vent system which is less prone to water infiltration.
  
   
• Leaks at flat roof scupper drains: Many flat roofs discharge water to an external metal scupper drain.
  
  This metal drain can freeze and trap water on the roof system. The drain may stay frozen much longer than the roof since it is not exposed to internal heat.
  
  Trapped water may accumulate to levels higher than the roof terminations or flashings, resulting in leakage.
  
  The short-term remedy is often to remove the downspouts and possibly break open the drain so there is discharge. Freezing of the drain often damages the surrounding roof, so a new drain and roof repairs are common in this situation. The long-term solution is to eliminate the scupper drain or replace it with a much larger drain system and/or installation of "heat tape" to a water migration pathway is used.
  
  
  
• Leaks associated with frozen gutters and downspouts: It is virtually impossible to remove ice from a frozen metal gutter or downspouts without damage. In many cases, the gutter system has to be removed from the roof to allow water to discharge and correct the leaking condition.
  
  The gutter has often been damaged by ice expansion and/or the removal process and cannot be reinstalled. In that situation, new gutters will be required. Be forewarned that removal of the gutters does not always completely correct "ice dams" that are caused by interior heat.
  
  Removing the gutters also may create a wet basement. The owner will be required to determine if the gutters should be removed and accepts associated liability.
  
  
  
• I never had a leak until my new roof was installed! This is a frustrating phenomenon for the new roof owner and roofing contractor. The source may be roof defect; however, in most cases, the source of the leak is heat warming the roof deck above the exterior temperature.
  
  The identical conditions, which are causing today's ice dam leak, may have never occurred before, or were unnoticed. When the snow is removed from the roof, the roof system can be inspected and tested to determine if there is a material or labor defect or ice damage. In most cases, the ongoing interior associated damage mandates emergency short-term procedures be taken.
  
  
  
• How do you know if heat is causing the problem? The simple way for a layperson to understand heat caused "ice dams" problems is to look at a non-heated detached building next to a heated building.
  
  It will be obviously apparent that the snow is melting in a different pattern on the heated building vs. the non-heated building. Non-heated buildings (garage) do not suffer from "ice dams." Furthermore, lowering the internal heat in a building often stops the leakage, again confirming the source to be interior heat.
  
  
  
• Caution- creating water mitigation pathways through snow often stops leaks but has not corrected the source of the leak. Roofs that have suffered "ice dam" leaks may not leak during rain.
  
  To avoid "ice dam" leaks in the future, one must create a system that assures the roof deck will remain cold during all weather conditions and/or install a back-up waterproofing system.
  
  Once an "ice dam" leak has occurred on a roof assembly and an "internal water migration pathway" has been established through the roof system, less severe conditions will cause leaks in the future.