February 1, 2010
Working in the snowiest parts of the United States creates many problems for roofs of all types, but special attention is needed to make sure a metal roof functions properly.
If the home is built with a simple A-frame design with entrances through the gable ends, then there is no question that metal is the easiest and most effective system in these adverse climates.
Getting architects to design a simple roof is as unrealistic as hoping your new copper top will stay bright and shiny for the next 30 years. Roofing professionals are required to do all they can to make a complex roof function with 3 feet of snow and ice on it.
Anatomy of a problemThe biggest problem most roofers encounter is known as an ice dam. These wintertime nightmares form at the eaves as a result of the unequal temperature between the cold eave and the warm roof over the living space. The heat loss from the attic - or vaulted ceiling - causes the snow to melt, and since the eaves are not heated, the water freezes, causing a buildup known as an ice dam.
The problem with an ice dam is that once it grows taller than the corresponding rise of the roof, it will hold pooled water behind it.
Many young roofers have been told to “think like a raindrop.” Great advice in the warm months, but with an ice dam on the eave it’s not a raindrop you see behind the ice but a fresh glacier “lake.” Since all pitched roofs are designed to shed this pooled water, it looks for the path of least resistance. Unfortunately that is straight through all those “covered” - but now immersed - fasteners securing the roofing material.
When all is said and done you must equalize the temperature difference on the roof in order to stop ice buildup. This can be done with a cold-roof design or by heating the eaves in some fashion. Since nothing is perfect, you must be realistic about the strength and weaknesses of each of these systems.
‘Cold' roofsA cold roof is basically one roof built over another roof with open airspace between the two surfaces. The airspace above the standard deck is open at the bottom of the eave and runs unobstructed all the way to the top of the ridge. The size of this airspace is dependent on many factors, including pitch, eave-to-ridge length, intake and exhaust length - and, of course, how cut up the roof is. If there is not enough intake or exhaust to keep the air flowing through the cavity, then a cold roof will never function. This resolution does not require a straight A-frame design, but it may not work and might require some amount of heat on the eave to resolve possible problems.
‘Hot' evesThere are many ways to solve ice dams using heat. The most simple is heat cable. This tried-and-true solution involves running heat cable on a zigzag pattern up and down the eve of the roof.
There is one thing that must be kept in mind with any heat system: If you start to melt the snow and ice, you need to keep contact between the heat systems from the top of the heat source all the way to the end of the downspout. Many installations do not function because the installers put the bottom of the zigzag right at the eve of the roof. Since the heat stopped 4 to 5 inches above the next cable (lying in the bottom of the gutter), the gutters freeze over and result in nothing more than an increase in the amount of water collecting in the ice dam. Heat cable (or any other heated eave system) must go over the drip edge and touch the cable in the bottom of the gutter - zip ties are great for making this happen - then return onto the roof and head up for the next loop on the zigzag pattern in order to function in the coldest of conditions.
The next rule of heated eves is that the system must go at least one foot above the warm wall. If a system only goes up onto the roof 6, 12 or even 18 inches, but the eaves are 3 feet long, you will have freezing between the top edge of the system and the heated area of the roof. This will still result in pooled water and worst of all, a leak. So any heated eave must run continually from one foot above the warm wall to the end of the down spout with no cold space between or you will still have ice (which does not flow) instead of water.
OptionsMany companies have developed ways of covering the heat cable with metal. This results in a larger area of melt by using the metal to transfer the heat over the pan. So long as the systems are able to produce top-to-bottom continuous heat, they are a much more effective solution than exposed heat cable. More importantly, to many homeowners they are more attractive and some heat cable manufactures give an extended warranty if the cable is not exposed to the weather.
What is even more popular than covered heat cable is the use of PEX hose with boilers as the heat source instead of cable in a covered system, much like a heated driveway or a radiant floor in a home. Radiant systems are able to produce much more controllable, reliable and cost-effective heat then any system using cable as the heat source.
Next time you are looking at a set of plans or a home to reroof in snow country take the time to try and figure out where the homeowners will have problems with snow and ice. Customers will appreciate your professionalism. Not all customers will want to solve the problems now but they will all be grateful that you are looking out for their best interests. If they don’t hire you or even if they do, but they don’t take your advice, you will still be the first person they think of when they have that dreaded leak, on the outside wall, at 4 p.m. in the middle of March when the temperature plummets after a sunny late winter day. The next thing they do will be to pick up the phone and call you.
Dennis Duce is a sales staffer at Nielco Roofing and Sheet Metal in Salt Lake City. For reprints of this article, contact Jill DeVries at (248) 244-1726 or e-mail firstname.lastname@example.org.