Snow Bracket Engineering: Is It Really Worth ItJune 13th, 2013
If you’re like most roofing contractors that work in the mountain regions of the United States and Canada, designing snow retention can be quite the chore. Often, a call to a snow retention manufacturer leaves a roofing contractor wondering how they will explain to the customer the number of snow brackets needed throughout the roof. It is often tempting for the roofing contractor to install just 1 or 2 or rows along the eave. Here are a few reasons a roofing contractor may install insufficient snow retention:
- “That’s the way the architect drew it on the plans”
- “The owner can’t afford so many snow retention devices”
- “I’ve seen the snow here, I think it’ll work”
- “The snow retention manufacturer is just trying to make extra money, I don’t really need this many”
- “I’ve never done this before, I have no idea what I need, I’ll just put on some of these that I found at my local roofing supply store”
None of these excuses are worth the liability and risk of damage that can occur. Designing snow retention is a refined science. If the right steps are not taken to design a system properly it is very likely to fail. Here is a list of some of the factors that must be considered when designing snow retention on any particular project
- Ground Snow Load
- Roof Slope/Pitch
- Roofing Substrate
- Roof Type
Studies have been performed across the United States and Canada to determine how much snow particular areas receive in pounds per square foot (psf), not inches or feet. A certain depth of snow often weighs more in a particular area than another. This is due to the different characteristics of snow; one foot of snow in the Sierra Nevada’s might be significantly heavier than one foot of snow in the Rocky Mountains. Local building departments are familiar with this information and often have a code required snow load. Obtaining the proper snow load information is the first step to designing a successful snow retention system.
These loads are then analyzed to determine how much weight is applied to the roof. After some engineering calculations your snow retention manufacturer should be able to calculate how much force the snow is placing on the snow retention devices and therefore be able to determine how many devices are needed on the roof. When too few snow retention devices are installed it becomes a matter of when and not if the snow brackets are going to fail, the math doesn’t lie, the snow retention will fail. The first severe winter will take them out.
It is critical that these calculations are performed; if not designing snow retention becomes no more than a guessing game. Often manufacturers receive calls from upset owners wanting to know why snow retention devices failed. Many times, these customers are not compensated by the manufacture because the snow retention devices were not engineered and installed properly.
Here is one example we ran across recently. For some unknown reason the roofing contractor decided that only 1 row of snow brackets was needed on this particular project. During the first winter the snow brackets failed leaving the owner shaking his head and poised for more roofing expenses. When snow retention devices fail, it becomes a matter of not just replacing the snow retention devices but also replacing other damaged items such as: gutters exhaust vents, roofing panels, etc. In this case the owner was lucky and the sliding snow did no additional damage.
Unfortunately, the owner not only had to pay to replace the damaged snow brackets but he also had to pay for additional snow brackets so he would have enough to bring it up to manufacturer recommendations. As you can see from the before and after photos the new design required 4 rows of snow brackets based on the design criteria for this area. The good news is the owner now has a system that is warranted, but more importantly one that will work! A quality snow retention manufacturer will warranty the product when installed correctly.
Here are some keys to follow when designing a snow retention system.
- Be prepared with an electronic or faxable roof plan showing the locations where you would like the snow retained. If you don’t have one, draw one.
- Make sure you have obtained the key design factors (snow load, roof slope/pitch, roof type, roof substrate).
- Make sure that you are working with a manufacture that will design the system based on the criteria mentioned above, and will provide you a drawn out plan.
- Become familiar with the various products available and their strengths and weaknesses, a good manufacture will take time to explain these to you.
When the time is taken to design and install a snow retention system correctly the system pays for itself. A properly designed snow retention system will prevent damage to the roof as well as people and property below the roof. And with many snow retention manufacturers the design is free!
By: Jacob Anderson