Heat Trace Cables: Avoid Dangerous Ice Buildup on Commercial Roofs
on Mon, 08/03/2015
These ice problems often occur when heat is lost through the roof of a building, causing the bottom layer of ice or snow to melt into water. If this water is not given a clear and direct path to a drain or collector box, it will continue to pool up until the weakest point in the roof either begins to leak water down into the building, or completely gives way, causing either severe structural damage or a complete roof collapse.
There are three main roof drainage systems used by commercial facilities: internal drainage, scupper drainage and traditional pitch and gutter drainage. Each has its own unique challenges and solutions for avoiding damaging ice buildup using heat trace cables.
The key function of heat trace cables in each situation is to enable the free and clear flow of water, which prevents the possibility of bottlenecks and slowdowns that lead to freezing and ice buildup. This is achieved by strategically placing heat trace cables in “freeze potential areas” throughout the roof where a clear flow of water is needed to properly drain the roof.
Internal Drainage RoofsThese roofs have one or multiple, centrally located drains that route water through piping systems within the building. Since the drains are integrated into the structure of the building and are exposed to heat from the top floor, they are less susceptible to ice buildup than exterior-located drains. However, these drains often fill with debris that will slow down the flow of water.
Given the weather conditions and the location of the drain, this blockage can cause melted snow or ice to remain on the roof and re-freeze around the drain. At this point the drain is blocked and the roof will continue to fill with water until another drainage path is found or until the roof begins to leak or collapse.
To prevent ice from building up around these drains, heat trace cables should be run through all valleys and drains on internal drainage roofs. A minimum of one cable needs to trace down into the drain until it reaches the heated portion of the building or until it is safe from possible freezing. As an additional precaution, heat trace cables can be placed in a star formation pointing outward around the edge of each drain to give the water every opportunity to quickly move through the drain.
Scupper Drained RoofsDrain collector boxes mounted to the exterior edge of a roof outside of a small parapet wall are commonly referred to as scuppers. Scupper drained roofs are pitched from the middle outwards to enable the roof to shed all water into the scuppers and then down the sides of the building through gutters.
These systems rely on the entire drain being located outside of the building, which naturally increases the potential of freezing and blockage from ice and snow. In some cases these exterior drains can become coated with hundreds or even thousands of pounds of ice, which in turn causes the roof to fill up with water until it leaks or collapses.
This potentially catastrophic situation can be prevented by not only routing heat trace cables from the center of the roof towards the exterior drains, but by configuring the cables in a star formation around each drain starting at the scupper on the opposite side of the parapet wall. This pattern pushes heat out into the area surrounding the drain and to make sure that enough surface area is available to create open pathways for water flow. If just one individual cable was used rather than the star formation, areas directly surrounding the scupper could become blocked with ice and cause the pathways to eventually be shut off.
Pitch and Gutter RoofsAs opposed to the previously mentioned roof drainage systems, pitch and gutter roofs simply rely on the slanted angle of the entire roof to carry all water to a gutter running the entire length of the lowest edge. This presents a unique challenge for heat trace cable application as there is no clear path that the water naturally gravitates towards.
Again, if the gutter becomes clogged with ice buildup, water will back up onto the roof and cause leakage or structural damage.
A heat trace solution for a pitched roof would first involve routing heat trace cables in all gutters and downspouts attached to the roof. From these, cables would need to be installed on the roof in a way that would keep any vulnerable pathways of water heated until they have fully vacated away from the building.
This could include edges, corners, and narrow pathways which water must flow through in order to reach the gutter. As previously mentioned, there is no specific route that water must take on a pitched roof, so it is up to the heat trace installer to anticipate freeze potential areas and take proper precautions to prevent ice buildup.
Considering the potential for water leakage and/or structural damage to commercial roofs due to ice buildup, heat trace cables are a practical investment for business owners with facilities exposed to severe winter weather. An initial investment in a heat trace system during the spring or summer months could prevent the cost of replacing a completely destroyed drainage system or a collapsed roof in the winter.
Article featured in Building Services Management Magazine.
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