Do you know the difference between a warm, a cold and an inverted flat roof?

Do you know the difference between a warm, a cold and an inverted flat roof?

There are different types of flat roofs. The roof construction determines whether the roof is referred to as a warm, a cold or an inverted roof. The main difference is the location where the insulation is installed with respect to the roof construction and the roof covering. This has a significant impact on the lifespan of the roof. In this article, you can read about the difference and the pros and cons of each construction method.

Most new builds have a warm flat roof

Today, most new builds in Belgium have a warm flat roof. In this roof construction, the insulation is installed above the load-bearing structure, on the vapour barrier, and then the roof covering is placed on top of it.

Optimal protection of insulation and roof construction

A warm roof provides significant advantages for the lifespan of the roof. This is because both the insulation material and the entire roof construction are optimally protected from external influences. This makes the roof less sensitive to expansion and contraction, reducing the risk of tearing or bursting of the roof covering.

In a warm roof, the insulation material is protected on both sides:

  • The roof covering protects the insulation from rain, wind, and other weather conditions.
  • A vapour barrier protects the insulation from moisture from the inside of the building.

A warm roof construction guarantees that the roof will last a long time and also that its insulation value will remain optimal.

A cold roof has a number of major drawbacks

In a cold roof, the insulation is installed below or between the load-bearing beams, on top of which the roof covering is installed. This method of installing a flat roof has several drawbacks. That is why warm or inverted roofs are generally the preferred options.

A cold roof has two major disadvantages:

  1. The timberwork sits right up against the roof covering and is therefore insufficiently protected against temperature variations. This makes the entire roof construction much more liable to expansion and contraction, which may cause the roof covering to tear or burst.
  2. While it is possible to install a vapour barrier below the insulation, it remains particularly difficult to ensure adequate ventilation with this construction method. This makes cold roofs sensitive to condensation, which may cause the wooden roof construction to rot.

An inverted roof is sometimes a cost-effective option

An inverted roof is a warm roof that is installed upside down. Here, the insulation is placed over the roof covering. This roof construction is sometimes used for roof terraces and for flat roofs with heavy foot traffic. For refurbishments, this method may offer advantages over a warm roof.

Ballast layer required

In an inverted roof, the insulation is installed over the roof covering. Logically, this can only be achieved using insulation specifically designed for this purpose. This material must, for example, be highly pressure-resistant. This method always requires a ballast layer to be placed on top of the insulation. This layer may consist of gravel, tiles, stones, etc. and serves to protect the insulation from erosion as well as to keep everything in place.

Roof refurbishment without major rework

Inverted roof construction is particularly advantageous if you want to refurbish your roof or install extra insulation. An inverted roof can be a cost-effective solution, particularly when the existing roof covering is still in good condition. In fact, with an inverted roof, you do not need to replace the roof covering and you can simply install the insulation over the existing roof. It allows you to refurbish your roof without any extensive work.

Disadvantages of an inverted flat roof

An inverted roof also has a number of disadvantages. For example, the insulation layer should not project beyond the roof edge and the roof should be able to support the extra weight of the ballast layer.

Moreover, an inverted roof will lose more heat and you will therefore have to use more insulation to obtain the same performance. To avoid moisture issues, the roof must also have a greater pitch.

In most cases, a warm roof is the ideal method for installing a durable flat roof. This method adequately protects the entire construction from outside and inside moisture. An inverted roof may provide a solution in some cases, especially when refurbishing a flat roof or installing extra insulation.

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