Hot Roof Vs. Cold Roof: Which One Is Better?
The terms “hot roof” and “cold roof” come up frequently when discussing roofing, but what do they really mean? What’s the difference between them? And which one is the better choice for your home?
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A hot roof is unvented and makes the attic space livable, but leaves the home more susceptible to ice dams. Cold roofs are the traditional roof assembly; they’re vented and provide better temperature regulation between the roof and living space. Generally, cold roofs are better for cooler climates, and hot roofs are ideal for pitched roofs.
What Is A Hot Roof?
A hot roof is a type of roof assembly that is unvented. Insulation is installed underneath the roof decking, leaving no space for ventilation. Without ventilation, the space is warmer, which is where the terminology “hot roof” came from.
Hot roofs are most often seen in new construction and structures with pitched roofs.
Pros of Hot Roofs
Below are the main benefits of having a hot roof.
Usable Attic Space
Depending on the house’s structure, the hot roof design allows the attic space to be usable and livable. This is because it brings the attic into the home’s thermal envelope. The attic space then maintains the same moisture and air control level as the rest of the house.
Contained Conditioned Air
With an unvented hot roof, conditioned air cannot escape the home. This means homeowners won’t be “heating (or cooling) the outdoors” and can save money on heating and air conditioning bills.
Energy Efficiency
Hot roof insulation ensures the insulation of the entire roof structure. In comparison to a cold roof, a hot roof is more energy-efficient.
Easy Installation
As long as the existing roof deck is in good condition, a hot roof is easy to install on top of it.
Cost-Effectiveness
The way a hot roof is insulated provides more thermal protection than a cold roof. With additional thermal protection comes more cost-effectiveness.
Cons of Hot Roofs
While there are many benefits of hot roofs, there are also several drawbacks to consider.
Necessary to Air-Seal Attic
Hot roofs with no ventilation mean more attention has to be paid to adequately air-sealing the attic.
High Installation Cost
Although hot roofs are cost-effective, they do have a relatively high installation cost. Hot roofs usually use spray foam insulation, which is more expensive than loose-fill or batt insulation. They also require the installation of an air barrier and vapor retarder to protect the attic from changing weather.
Chance of Moisture, Mold, and Ice Damming
The main characteristic of a hot roof is that it has no ventilation. However, this means that there’s a higher chance for the accumulation of moisture, which can lead to mold. It also means that hot roofs are more susceptible to ice damming than cold roofs.
Ice damming occurs when an ice ridge forms at the roof’s edge. This ridge prevents melting ice from draining off of the roof. As a result, water and ice build up, push under the roof’s shingles and make their way into the home.
This can cause significant weight loads on the roof that are too much for the structure to handle. Ice dams can also lead to damage to insulation, ceilings, walls, and other areas of the home.
Increased Building Height and Higher Roof Profile
Another drawback of a hot roof is that the building’s overall height will be increased due to the higher roof profile.
Decreased Ceiling Height
Because of the insulation required for a hot roof, the ceiling height of the attic will be decreased. Doors and windows may be impeded due to the insulation as well. They may not be able to open properly because of the way a hot roof is installed.
What Is A Cold Roof?
A cold roof, also known as a vented roof, has been the traditional roof assembly for decades. The attic is not part of the home’s conditioned space with cold roofs. Instead, insulation separates the air between the conditioned space and the attic space.
Cold roofs must have a ventilation baffle, a ridge vent or gable vent, and soffit vents. Insulation is laid between the rafters. Air can freely flow under the roof’s sheathing.
The assembly of cold roofs is considered to be simple and low-impact.
Pros of Cold Roofs
Here are some of the main advantages of having a cold roof.
Cooler In Summer
Cold roofs keep homes cooler in the summer, resulting in lower cooling costs.
No Ice Dams
Since the roof remains cool in the winter, a properly installed cold roof prevents ice damming. Ice dams can lead to major damage to your home, so their prevention is extremely important.
Better Temperature Regulation
In warm climates, the ventilation of a cold roof regulates temperature differentiation between the house and the roof. For example, if the sun beats down on the roof, that heat can’t easily transfer into the home’s living space.
Easy Installation During Construction
If a cold roof is installed during construction, the insulation can quickly and easily be applied.
No Change to Building Profile
The insulation used for a cold roof is low-impact and doesn’t affect the height or profile of the building.
Cons of Cold Roofs
Just like hot roofs, cold roofs also have a few drawbacks to keep in mind.
Difficult to Install After Construction
Less Thermal Efficiency
In comparison to hot roofs, cold roofs are less thermally efficient.
Necessary To Seal Attic
Similar to hot roofs, cold roofs must be air-sealed. This way, the conditioned air will not mix with the outside air. If the attic isn’t properly sealed, the HVAC system will have to work harder. This can increase heating and cooling bills and require the system to be replaced sooner.
Hot Roof vs. Cold Roof: Evaluation Criteria
Here we will directly compare hot and cold roofs using a few different evaluation criteria.
Climate
In general, hot roofs are not very suitable for cooler climates. This is because hot roofs are more susceptible to ice dams, which can cause major damage to homes. In cold climates, a cold roof is usually the better choice.
This isn’t to say that hot roofs will automatically lead to ice damming, mold, and issues with moisture. A properly air-sealed attic shouldn’t have these issues. The problem is that these problems tend to be less noticeable in a structure with a hot roof.
In warmer climates, both hot roofs and cold roofs can work well. However, cold roofs in hot climates usually have the best savings when it comes to cooling bills.
Homeowner Needs
If a homeowner wants their attic to be usable or even a living space, then a hot roof is best. This is because, with a hot roof, the attic is generally the same temperature as the rest of the house. It will have the same air control and moisture level as the other living areas.
Building Plans
Depending on the building plans for a home or other structure, one roof type may be better than the other. Generally, warm roofs are easier to install. They add height to flat roofs and are more ideal for pitched roofs, but they also have great thermal performance.
Structures with rooftop balconies, flat roof extensions, or doors leading onto the roof aren’t eligible for hot roofs. For houses like these, a cold roof is the only option.
Cold roofs are easy to install when done during the initial construction phase. But if homeowners want to make their roof into a cold roof after construction, it’s definitely challenging. Installing a cold roof after construction involves removing the current roof, adding insulation, and then replacing it.
Related Questions
What is the difference between a hot and cold roof?
The main difference between a hot roof and a cold roof is the location of the insulation. A hot roof’s insulation is located on top of the existing roof’s surface. Conversely, a cold roof’s insulation is located between the rafters.
How hot do roofs get?
It depends on the temperature outdoors and the type of roofing material. In some cases, roof temperature can be as high as 170 degrees Fahrenheit.
Why does a cold roof need ventilation?
A cold roof needs ventilation so that heat can escape from under the shingles.
Hot Roof vs. Cold Roof: The Final Verdict
Overall, hot roofs and cold roofs both have their pros and cons. Each is more suited to certain climates and situations.
Hot roofs are energy-efficient, easy to install, and contain conditioned air. They make attics into livable spaces. But they come with a high installation cost and an increased chance of ice damming and water damage.
Cold roofs are better for temperature regulation and are less susceptible to ice dams. They don’t change the building’s height or profile. However, they’re difficult to install after construction and are less thermally efficient.
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With a lifelong passion for writing plus strong enthusiasm for home improvement and DIY projects, joining the team at Upgraded Home was an easy choice. Jessica Allen likes to share helpful information with current and aspiring homeowners. Aside from writing, Jessica loves doing yoga, playing the piano, and dabbling in graphic design.
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