Is spray foam the solution, though? Does spray foam insulation prevent ice dams?
Before a homeowner decides to move forward on an insulation project, it’s important to discuss what their expectations are for ice dams and insulation. This way their spray foam contractor can discuss how foam can help, but also any factors that can still lead to the formation of ice dams.
In this article, I’ll discuss how ice dams form, explore if spray foam will totally prevent ice dams, and discuss any factors that can impact the foam’s effectiveness.
What is an Ice Dam and How Do They Form?
An ice dam is a layer of water that freezes on the roof of a home, usually underneath a layer of snow and adjacent to icicles that form on the overhang.
These ice dams cause damage that leads to openings in the roof and water leaks that run into the attic. Those pesky water spots on the ceiling of a home are from the water leakage in the roof.
Ice dams form when the warm air from the main living area leaks into the attic and heats up the roof. The snow and ice on the roof melts, running down the roof under the remaining snow. Once it hits the freezing cold soffit overhang area, the water refreezes and traps ice under the shingles and creates long icicles that can hang dangerously down to the ground.
Will Spray Foam Insulation in the Attic Prevent Ice Dams?
Since heat loss through the roof is the root cause of ice dams, spray foam insulation can definitely help prevent ice dams because it helps to regulate heat loss.
More specifically, spray foam insulation on the roof deck of an attic, creating an unvented attic, can definitely help with that issue.
Keep in mind, you want to establish your building envelope on the outside layer of the house. In this case, we're talking about the roof so you want your building envelope directly on the underside of the roof area. This will help to keep the snow from melting on the roof in the first place.
The same can be true for cathedral ceilings, but they present their own issues which will be discussed below.
Factors that Impact the Prevention of Ice Dams
While spray foam can help, ice dams can still form on your roof under certain conditions.
Radiant waves from the sun alone can cause ice dams. The sun is hot, so it only makes sense that it will cause the snow to melt in spots.
The outside temperature also plays a role. If the weather drastically takes a turn to the warmer, which we typically see happen at some point during the winter each year, then the snow will melt. This will happen even after the installation of spray foam.
If the homeowner has a cathedral ceiling, then thermal bridging will likely cause the formation of ice dams. Thermal bridging is when there is a break in the building envelope. Basically, there is any direct physical connection from the inside to the outside of the house, like the wood studs.
Spray Foam Insulation and Ice Dams
Ice dams can cause serious damage to the roof of a home, so a homeowner needs to have the correct expectations when they want to prevent them.
At the end of the day, Mother Nature and the laws of thermal bridging may be a never-ending battle in the prevention of ice dams. Applying spray foam insulation on the roof deck will establish the building envelope, creating an air seal to help prevent heat loss through the roof helping to prevent ice dams or greatly reducing them.
It is always best to have an experienced spray foam contractor review your home to determine the best plan of action for your specific situation.
Eric brings his knowledge and training in building science, training in spray and injection foams from the manufacturers, more than 8 years installing foam insulation, as well as selling and managing in the foam insulation industry. He is also BPI and Dale Carnegie certified and has taken several building science courses including air sealing and building envelope.
Eric’s responsibilities include overseeing and giving support to all of the branches of the RetroFoam of Michigan company, office, estimates, and installs. He is also the Professor of Foam on our educational YouTube series Foam University.
Even when Eric is off he is usually still “working” or thinking about work, but when he can get away he enjoys camping, hiking, hunting, and woodwork.