Cathedral Roof: Heating, Insulation, and Ventilation

The cathedral roof (or cathedral ceiling) was first introduced in the 1960s and 1970s. This type of roof is aesthetic and adds a unique flair to any home. The cathedral ceiling accentuates the interior appearance of a home by exposing the slope of the roof. Constantly modernized and revamped, the cathedral roof is most commonly a feature in chalets and country houses.

If your home has this type of roof, or if you are planning on building one just like it, surely you will want to know the specific characteristics of this type of design. These so-called "sloped" roofs are prone to snow build-up. Moreover, the issue related to insulation and ventilation is fundamental to ensure your comfort and the durability of your home.

As you read this article, you will learn everything you need to know about heating, insulation, and ventilation systems for a cathedral roof.

Heating a Cathedral Ceiling

However gracious the cathedral ceiling might be – accentuating your interior space – buyer beware because it can also become a money pit of wasted heat if you fail to choose the right heating system.

Most homes rely on convection heaters, a device that heats up all the air in the room. However, the cathedral roof has particular characteristics that directly affect the distribution of heat. Due to the height of the roof, the heat produced by the heating system generally tends to be absorbed near the ceiling.

This is purely the laws of physics at play. Hot air being lighter than cool air, the former will naturally rise (principle of the hot-air balloon). As a matter of fact, if we consider the concept as it should be, heat does not rise, but rather it is the medium that does.

Therefore, it is pretty difficult to use a standard heater when you have a cathedral roof. Since the warm air will rise, you will not benefit as much from the heat.

Not only will your comfort level be negatively impacted, but if your roof is poorly insulated, the heat may also dissipate through it. Rest assured, as this kind of roof is very common, there are heating systems adapted to cathedral ceilings.

Photo: Pixabay

Radiant Convectors

Radiant heating systems allow you to heat your home in an optimal way. If properly installed, this system provides an even amount of heat throughout your home. Radiant convectors provide an exceptional level of comfort at relatively low ambient temperatures, making these systems energy-efficient.

Radiant heating systems rely on the emission of infrared waves from the ground. The radiation is transmitted through the air with virtually no loss and subsequently heats the walls and floor while warming the circulating air. Those in the radiant zone will also be able to feel the warmth of the room.

There are several types of radiant heating systems, but the most prevalent is heated floors, mainly because of the level of comfort these provide. Floor heating systems are available in a variety of forms, including electric, resistance, and hydronic systems. Note that hydronic systems are compatible with different types of heating systems, such as geothermal systems.

Photo credit: Wikipedia Commons

A radiant heating system can be great for new buildings, but with existing structures, some work will need to be done to make the installation possible. To avoid this type of inconvenience, there is another alternative: install one or more ceiling fans to redirect the heat toward the floor.

If you choose this approach, we suggest that you opt for a unit that can be reversed, so that you can benefit from it both in the summertime and wintertime. You can use an electric radiator or a fan coil unit which, combined with a heat pump, will ensure thermal comfort at all times.

Insulating a Cathedral Roof

Roofs built in the 1960s are often poorly insulated and leaky. This results in increased heating costs, ice build-up on the eaves, and reduces the overall durability of the roof. Natural Resources Canada considers the insulation work on a cathedral roof to be quite difficult and strongly urges using the services of a qualified contractor.

Nevertheless, you can carry out the necessary maintenance to ensure the insulation in your roof is functioning properly. Here are some telltale signs:

• High energy consumption (heating during winter and air conditioning during summer);

• Overheating is caused by a lack of ventilation during the summer;

• Mould growth and water infiltration;

• Ice build-up on the roof;

• Condensation and rot in the attic;

• Lack of temperature control and comfort in the rooms.

Photo: Pixabay

As previously mentioned, insulation problems are mainly associated with older buildings; during the 1960s, the height of rafters was 8 to 10 inches (20 to 25 cm), but for proper insulation and ventilation, you need about 15 inches (38 cm). Two forms of insulation are possible:

Insulating from the Inside

Technically speaking, internal insulation is possible, but it is difficult to ensure perfect airtightness when proceeding with this method. An option would be to apply blown-in cellulose insulation between the interior finish and the structural part of the house. On the other hand, should the space not allow for it, EcoHome has other suggestions to insulate the roof of your home from the inside:

• Strip any existing plaster and add rigid insulation right over the structure and any insulation already in place;

• Add furring strips under the structural frame before adding the rigid insulation;

• Add an additional structure (2 x 4) under the frame, then add loose-fill insulation such as cellulose.

Insulating from the Exterior

When installing roof insulation, ensure that there is sufficient room for proper ventilation. Once again, EcoHome strongly suggests applying a layer of sprayed polyurethane (2 to 3 inches) to cut all thermal bridges and make the whole thing airtight. Then, simply round out the insulation with materials that offer the best thermal performance. 

Airing Out a Cathedral Roof

The National Building Code of Canada requires all roofs, regardless of their shape, to have proper ventilation as lack of airflow causes moisture build-up and rot in attics. Since cathedral roofs represent a relatively big market, several manufacturers provide products that are perfectly adapted to this type of roofing.

Optimum, which is a company that specializes in structural ventilation systems, developed a static ventilation system specifically for cathedral roofs. This device prevents hot and humid air from entering the attic space before said air condenses. Since the air constantly circulates between soffits toward the roof ventilation system, it ensures constant efficiency.

Photo credit: Ventilation Optimum