Home technology expert Ross Trethewey helps a homeowner solve their attic insulation problem. After getting some conflicting suggestions, the homeowner turns to Ross’s plan of turning it into an unvented attic space with spray foam insulation. Ross walks the homeowner through testing the home, installing the insulation, and testing the insulation quality.
What are Ice Dams?
An ice dam occurs when the heat from the home rises and melts snow on the roof, the snow melt (water) runs down the roof toward the unheated eve, and refreezes, creating a dam. The dam then causes more snow melt to back up, allowing it to seep under the shingles and into the home. This can cause damage to roof decking, insulation, drywall, and other materials, and the answer is insulation.
Two Types of Attic Insulation
Attic insulation falls into two categories, vented and unvented. The difference is airflow and the location of the attic insulation.
- A vented attic has vents on either end of the attic (known as gable vents), and the insulation is in the floor. This cuts down on the amount of space that the HVAC system has to heat or cool while allowing the attic space to breathe along with the outdoor conditions. However, these attics aren’t great candidates for storage or air handler placement. Also, they’re prone to leaking, allowing warm air to rise from within the home around lights, vents, and other penetrations into the attic space.
- An unvented attic is the opposite. In these spaces, the roof is insulated, essentially putting an insulation hat on the home and conditioning all of the space underneath. These attics don’t breathe well and do use some of the home’s heating and cooling energy, but they’re great for storage and air handlers. And, if there are penetrations leaking air into the attic, the home is able to retain that air in the conditioned envelope to improve efficiency and keep ice dams from forming.
In either of these cases, the idea is to insulate the entire roof to prevent premature snow melt that will freeze when it reaches the home’s eave.
Testing for Leaks
One of the ways to choose the proper attic insulation is to test for leaks. Experts can come into the home, set up a blower door (a fan that fits within a door), and put the home into negative pressure by ejecting the air within the home. At that point, the expert will take readings at different locations to test the air pressure change. Maybe more importantly, they will also test the different penetrations with canned smoke to see how much air is leaking into the attic.
Another aspect of choosing the right type of insulation revolves around the actual HVAC mechanicals. If there is an air conditioning unit or furnace in the attic space, an unvented attic is the way to go.
Spray Foam Insulation to Prevent Ice Dams
When it comes to preventing ice dams, spray foam insulation installed in an unvented attic is a great choice. Closed-cell spray foam is moisture resistant. This isn’t typically a DIY project, as it’s important that the installer have the proper license, permit, and experience to work with this type of insulation.
The contractor will remove the existing insulation, spray foam down into the eves and the underside of the entire roof to the appropriate thickness while safely handling VOCs (volatile organic compounds). This relatively complex procedure takes experience and specialized techniques and equipment.
This insulation type will allow the home to retain heat and moisture rather than allowing it to condense on the backside of the roof sheathing. It will also keep the exterior of the roof at a consistent temperature, preventing water from melting, running down the roof, and freezing again.
Ross helps a homeowner suffering from ice dams by first discussing attic insulation options for vented and unvented roof systems. They then decide which system is best for the homeowner. Afterward, installers install spray foam insulation to the attic roof rafters.
Ross performs a blower door test—he depressurizes the home by pulling the house under negative
pressure, sending all the interior air through the fan, outside.
Ross performs zonal pressure diagnostics with a manometer—he measures differences in pressure
between rooms to determine where the air is leaking.
Ross checks the air leakage from the attic to the main floor by looking at vents and light fixtures
with a thermal imaging camera.
The installers apply a new industry-standard spray foam that requires only a single application
and will expand to a 5” thickness.
Expert assistance for insulation was provided by Green Stamp Co. Additional assistance was provided by Holcim.