What You Need To Know

While a good old fashioned Canadian snowstorm may be great for snowball fights, avid skiers and create some wonderful winter landscapes, no one really enjoys having to shovel all that snow. Even worse, while you are outside clearing the driveway snow, you notice those large drifts accumulating on the roof and overhanging the eaves.

This brings us to a question I hear every winter. Do I need to shovel off my roof?

Generally speaking, experts in structural engineering say no! In Southern Ontario roof structures are engineered based on a 50-year average, to carry an average snow load of 60 pounds per square foot. I say average snow load because sloped roofing is engineered to carry the load to the outside foundation walls. Although there is some direct load across the field of the roof, most of the weight is transferred down, so steeper pitched roofs will carry more load than a shallow pitched roof. The same goes for commercial flat roofs, they are designed by structural engineers to carry snow and water loads. With the exception of older buildings, typically pre 1970 in most areas when snow loads first became factored into building requirements, our southern Ontario residential sloped roofs and commercial flat roofs are designed and engineered to carry our Canadian winter snow loads. So in answer to the question, to shovel or not to shove your roof, in most cases the answer is no!

For the most part, it’s an extremely dangerous proposition to ascend your roof, and even more so in winter. If for any reason you have an issue with leaks or ice damming at eaves, please call in a professional. Secondly, removing the snow from your roof is generally not necessary and can be extremely expensive if you call in a roofing contractor to do so. Most contractors promoting snow removal in Southern Ontario are just out to steal your money, so leave the snow where it belongs, on the roof!  However, If you have an older building or residence that you are concerned about, you may want to call in a structural engineering firm to assess the roof structures’ integrity and load capabilities.

Exceptions to the Rule

Commercial Flat Roofs – Snow may drift over mechanical and HVAC equipment. These areas need to be cleared. Also, clear all drains.

Residential Roofing – Roof ice dams forming at the eaves areas of the roof need to be addressed as the dam will contain the snow meltwater which in turn will back up under shingles and valley areas causing roof leakage. Ice and Water Shield leak barrier installed with most new shingle roofs today, may or may not offer some protection. It will depend on how large or how far the dam extends up the slope of the roof. Underlay protection will provide no benefit in the prevention of leaks caused by ice damming.  

Roof Ice Damming

Causes – Ice damming occurs when snow warmed by inside attic temperatures causes the snow to melt at the bottom or roof side and runs under the snow pack, freezing at the unheated soffit overhang or eave areas. Roof Ice dams will never get smaller and only continue to build upon themselves in the cold winter months. Ice damming is preventable but the prevention needs to be effected in warmer weather months. Once an ice dam occurs it is to little to late to effect any prevention, you can only treat the problem. Roof Ice dams occur for one or more reasons that need to be addressed and corrected.

A. Insufficient roof ventilation.

B. Unevenly distributed roof ventilation

C. Poor attic insulation

D. Improperly installed attic insulation. Installed without soffit baffles and blocks or fills the soffit areas of the attic.

E. Inadequate soffit ventilation

Roof ice dam removal

First of all, do not attempt this yourself as it is extremely dangerous. You can contact Tops Roofing Company for all roofing repair and roof ice dams prevention and treatments or another trained roofing contractor or roof professional.

Chopping away at an ice dam with hammers, mallets, picks, and axes is a very bad idea, as you will ultimately damage the underlying roofing materials causing even greater problems and roof leaks. Roof Ice dams do not need to be cleared in their entirety, but rather only channels need to be created to allow contained water to drain. These channels can be mostly created by clearing any snow away and then using a nylon or pantyhose leg filled with calcium chloride, positioned upon the ice dam to melt and create a channel.

  • Do not use ice melt types of road salts as they are extremely corrosive and will damage painted surfaces, shingles gardens, shrubs, and plants. Extremely large or well-formed roof ice dams may need professional removal or channel creation by experienced roofing professionals.

Roof ice dam prevention

The key to preventing roof ice dams is to maintain your attic temperature close to or at, the outside air temperature.

  1. Insulation – have your attic insulation inspected and R-value assed and then topped up to a minimum of R 50. Ensure attic hatches are properly sealed. Install soffit baffles on top of the insulation to allow air exchange in attic spaces.
  2. Roof Ventilation – Ensure proper distribution and sufficient roof venting based on attic flat inside square footage. Ensure all bathroom exhaust vents and roof dryer vent pipes are correctly fastened, sealed, and insulated.
  3. Soffit Ventilation – As air draws in from the soffits and is exchanged through the roof vents, sufficient soffit ventilation is required. At Tops Roofing Company we recommend the continuous type of soffit venting or in older homes with wood soffit, a minimum of one vent every 6 linear feet.

De Icing Heat Cables

De-icing or roof heat cables can often be used in areas with no attic access or problematic areas of the roof that seem to be prone to the collection of drifting snow and resulting ice formation or dams. Heat cables are a preventative measure and will have no effect on already formed ice or roof ice dams, They can also be used solely for eavestroughs and drain pipes or in conjunction with a roof application. They must be installed in warm weather months, plugged in in November, and left until spring.