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Warm Roof vs. Cold Roof

When you think of roofs, chances are you believe the only way they could be warm or cold is in the summer or winter. The truth is, flat roofs come in two different configurations depending on how the architect designed it.

The difference between the two types of roofs is rather simple when you look at it, however, the initial cost of construction and the overall cost savings between the two are quite significant.

Cold roof construction is the traditional method of building roofs both flat and sloped. It has been used by builders for years. It is easy to construct and far less expensive than construction of a warm roof.

What does it involve?

Cold roof construction, is what is found on most older flat roof buildings and almost all houses both old and new. In a cold roof installation, the insulation is placed below the roof rafters. This means that anything above the ceiling of the uppermost area of the building, is cooler than the living space. Warm, moisture-laden air is allowed to flow through the insulation and when it comes in contact with the colder sub-structure of the roof, condensation can form on the structure of the roof. Proper ventilation is required to remove any air that infiltrates the space above the insulation thus preventing condensation from forming.

This method of construction works well for most situations if the proper ventilation is installed from the start. However, it is not the most energy-efficient method and thick layers of insulation are required to prevent heat loss through the non-insulated areas. It is, however, the cheapest and easiest form of roof construction and widely popular.

The second type of roof construction is the warm roof.

Warm roof construction involves laying rigid insulation on top of the roof rafters. This allows the area below the insulation to be as warm as the living areas. This method is now widely used in the flat roof industry, but it is very difficult and expensive to adapt this type of insulation to a sloped residential style roof. Hence why it is not widely used.

A warm roof has many benefits over a cold roof installation. It is more thermally efficient and despite its higher cost of construction, lessens overall heating costs, thus saving money over the long-run. A flat roof installation, due to the warm air being held below the solid surface of the roof, does not need to be ventilated. There is no air-space between the roof and the warm air, thus there is no condensation.

When designing a warm roof, the architect must take the added weight of the insulation into consideration. This is especially true in residential construction of a sloped roof. A sloped roof done with standard construction is not capable of handling the additional weight of insulation so stronger roof trusses must be used.

If you are thinking of building a new building or home, talk to your architect about warm roof options and how much money you will save in energy costs over time. In most cases, the cost savings outweigh the initial expense. If you are thinking of re-roofing your home or building, the option of a cold or warm roof is already done for you. The roof must be designed to withstand the additional weight of the warm roof or the entire roof must be reconstructed. In most situations you have to live with whatever roof your building or house came with.