Flat roof elements: the structure of the roof pie and its features

Modern and sleek flat roofs are a sleek replacement for conventional pitched roofs and are frequently seen in urban and contemporary architectural designs. It is crucial for both homeowners and builders to comprehend the flat roof structure, also known as the roof pie. Flat roofs are constructed and function differently than pitched roofs, which have a steep slope. Instead, flat roofs have a very slight incline, or none at all.

The fundamental elements of a flat roof are made up of multiple layers, each of which is essential to the building’s longevity and protection from the elements. A flat roof usually consists of a waterproof membrane, insulation, vapor barrier, and structural deck. Together, these layers produce a strong barrier against rain, snow, and UV rays, as well as thermal insulation and moisture buildup prevention.

The ability of flat roofs to accommodate extra components like HVAC units, solar panels, and roof gardens is one of their distinguishing features. Because of their level surface, flat roofs are more practical for urban residential and commercial buildings because they can make better use of available space, something that pitched roofs cannot.

Regular inspections are necessary to maintain a flat roof in order to look for wear, water ponding, or membrane damage. In order to avoid water pooling, which eventually can cause leaks and structural problems, proper drainage is essential. Comprehending these facets of flat roof development facilitates knowledgeable decision-making regarding installation, upkeep, and improvements for buildings for both professionals and homeowners.

What roof is called flat?

Let’s begin with the fundamentals. The flat roof actually only creates the illusion of complete horizontality from a visual standpoint. A slight slope of 1 to 5 degrees (1.7-8.7%) still exists. Its primary function is to permit atmospheric precipitation to freely flow to the points of water collection; visually, it is completely unnecessary during operation.

In contrast to their pitched counterparts, flat roofs are horizontal overlaps supported by the building’s walls rather than having rafter frames. Its unique quality lies in the reinforced heat and waterproofing layers that are required because of a roof’s environmental message.

The following benefits make a flat roof an appealing option for developers:

  1. Reduced price. Compared to the pitched roof, a flat analogue has a smaller area, respectively, the costs of materials are below.
  2. Simplified installation and further maintenance. The arrangement of a flat structure is easier than the pitched, since moving on a horizontal plane is easier than on an inclined. For the same reason, various measures for servicing the roof itself and the devices (chimneys, fans, antennas, etc.P.).
  3. The possibility of obtaining additional useful area (with the operated roof). The surface of the flat roof can be easily used as a terrace, a walking platform, and even … a garden with a real lawn.

A sturdy base, such as reinforced concrete slabs, plywood, corrugated board or a continuous surface of boards, OSP, or CSP (if the flat roof is supported by wooden beams), is essential to its structural integrity. The actual roof coating is composed of multiple layers. The type and function of the roof determines their quantity, placement within the design, and composition during production.

Many kinds of flat roofs

  • Unpromised roof. The simplest, not carrying any additional functions, except for the protection of the room from the influence of the environment. It is not used to arrange recreational or economic places. Everything that is required of it is a sufficient protective function, the ability to withstand snow and wind loads, as well as the weight of workers conducting service measures. That is, during the construction of such a roof, the calculation is carried out on the fact that 1-2 people can be on it at the same time, not constantly, but only for the time of maintenance and repair of the coating.
  • Operated roof. Equipped to perform some additional functions, except for directly roofing. For example, on operated roofs, sports grounds, terraces, parking lots are arranged, lawns are planted and flower beds are broken.
  • Inversion roof. Characterized by non -traditional placement of layers – thermal insulation mats (EPS) are laid almost in the very top of the pie. Waterproofing is mounted under a layer of insulation. This solution helps extend the service life of the waterproofing coating, and, accordingly, the roof itself. Inversion roofs can be both operated (most often) or unpromitable.

In this piece for "All about the Roof," we explore the many moving parts of flat roofs, with a particular emphasis on the special framework called the roof pie. This fundamental structure consists of layers that are necessary for structural integrity, waterproofing, and insulation. We examine the critical roles that every layer—from protective membranes to insulating materials—plays in boosting weather resistance and durability. Knowing these components helps professionals and homeowners alike make educated decisions about maintenance and upgrades while also illuminating the intricacy of flat roof construction."

The structure of the pie of the flat roof

Every kind of flat roof has unique structural characteristics that permit the application of particular materials and arrange layers in a particular order.

Unexploited classical roof

Waterproofing coatings such as polymer membranes, roofing masters, bitumen melted materials, and roofing material make up the final layer of these kinds of roofs. Such a roof is not intended for extended human occupancy or operation, and as a result, the waterproofing layer’s protection is not offered.

Moreover, thermal insulation is not required. Insulated and unsubstantiated unexploited roofs are classified based on the existence of this layer.

The heat-insulating layer of the insulated roof is contained within its structure and is shielded from the outside by waterproofing and a vapor barrier at the base. Many residential, civil, and industrial buildings are constructed with this type of roof because insulation is readily available.

The insulated, underutilized roof’s layers are arranged in the following order (though this order may change slightly):

  • base;
  • sloping layer (if necessary);
  • vapor barrier;
  • insulation;
  • waterproofing (roofing).

Most often, reinforced concrete slabs or a metal profile serve as the foundation for an insulated unutilized roof; plywood for wooden beams and the bases of boards, OSP, and CSP are used less frequently. A sloping layer that determines the direction of water flow from the roof is added to the base if needed. Usually, loose materials and screed—concrete or expanded clay concrete—are used to form the slope.

This is how a vapor barrier layer is mounted on the base to shield the insulation from wet steam rising up from the side of the room. You can use roofing material, pergamine, and films made of polyethylene and polypropylene as a vapor barrier. Subsequently, a waterproofing carpet composed of bituminous materials or polymer membranes sits atop one or two layers of insulation materials (mineral wool, foam, or EPPS).

Similar layers are used to form the unscarried non-sequencable roof; however, the vapor barrier and thermal insulation are not required in this version.

Used roofing layers:

  • base;
  • sloping layer (if necessary);
  • Roofing.

Operated classic roof

A more intricate layout. varies from the preceding choice in that it has an upper durable layer that helps to set up an operating platform. Usually, paving slabs, a terrace board, gravel, or gravelly are used for this purpose.

It is possible to arrange the operable roof above the residential building or over the garage’s premises. As a result, this design is dishonest and insulated.

The insulated roof’s common structure is as follows:

  • base;
  • sloping layer (if necessary);
  • vapor barrier;
  • insulation;
  • waterproofing;
  • dividing and filtering layer (geotextiles);
  • paving slabs for preparation.

In the video, one of the options for the insulated operated roof device is displayed, along with a thorough analysis of every component:

Thermal insulation is not present in the unscarried operated roof. Consequently, a vapor barrier film is not utilized in this instance to safeguard the insulation. If not, the structure is the same but higher than the option that was thought of.

Inversion roof

This is a unique instance of an insulated roof that has been misused and is not in use. A waterproofing barrier is always placed on top of the insulation in a traditional roofing structure.

The layers are reversed in the inversion roof. The heat insulator is moved beneath the waterproofing membrane. If the insulation is shielded from the elements by a waterproofing carpet in a traditional roof, this is not the case in an inversion; rather, it is the opposite. Waterproofing is shielded by a layer of thermal insulation.

By using such a solution, you can avoid a major problem with traditional roofing structures: the waterproofing carpet quickly deteriorates due to temperature fluctuations, UV rays, and atmospheric effects. Because inversion roofs do not have this structural flaw, the waterproofing carpet has a significantly longer lifespan.

The layers of an inversion-style flat roof are arranged as follows:

  • base;
  • sloping layer (if necessary);
  • waterproofing;
  • insulation;
  • drainage layer;
  • geotextiles;
  • Protective finish layer – gravel or gravel ballast, tiles, terrace board, etc.

The following principle is used to operate the inversional roof device. First, an insulating layer is placed over a waterproofing barrier on the base. Geotextiles and drainage come next. The top layer, which is often formed of embankments, serves as protection.

The vapor barrier is not incorporated into the inversion roof’s structure. As a result, steam escaping from the interior may damage the insulation. Additionally, nothing from atmospheric precipitation can cover the insulation from above (waterproofing, which in this version is hidden in the lower layer of the pie, performs the protection function in traditional roofs). As a result, specific specifications are placed on the insulation, the first of which being low absorption of steam and water. These properties are found in extruded polystyrene foam (EPS) mats, which are most frequently utilized in the construction of inversion roofs.

In an URSA training video, the stages of the inversion roof device are demonstrated:

Arrangement of a drain system

As was previously mentioned, the flat roof is not perfectly horizontal; rather, it has a slight slope (up to 5 °) that is utilized to support the drainage system’s device.

There are various ways the slope is formed.

  • If the base of the roof is the railway plate, then the slop is performed using filling materials (expanded clay, crushed stone, perlite), concrete and expanded clay concrete screed, insulation plates.
  • If the roof is arranged on wooden beams, then the slope is provided either by the initial laying of the beams at a slight angle, or with additional installation of the lag of different thicknesses with a slope in the required direction.
  • When used as a base of profiled metal, its styling is initially carried out under the necessary slope.

The equipment of drains, which may be internal or external, requires the slope.

The slope is eliminated to water intake funnels or fittings that are situated on the roof’s surface once the internal drain is installed. Their quantity and placement are determined by the roof’s area, operational parameters, and local precipitation levels. Typically, 200–300 m 2 roofs have one funnel installed.

Every funnel has a filter installed inside of it to keep small animals, branches, and leaves out of the drain. Some funeral models come with self-regulating thermal cables to keep the water from freezing. Even in the winter, during thaws, they aid in the unimpeded removal of atmospheric moisture.

Large industrial buildings typically use the internal drain. External water systems are more common in private construction. The spilled holes, or overflowing windows, are placed at the corners of the parapet along with the storm in this instance, where the slope is led from the center of the roof to the edges. Heating cables should be added to such a system in order to prevent overflowing windows and icing storm windows during the winter.

Flat roof structure The flat roof typically consists of several layers:
1. Roof Deck The base layer, often made of plywood or concrete, provides structural support.
2. Vapor Barrier This layer prevents moisture from penetrating into the roof construction.
3. Insulation Helps regulate temperature and energy efficiency.
4. Membrane Waterproof layer that shields against weather elements.

Recognizing the essential elements of a flat roof’s structure is necessary to comprehend it. Usually, the roof "pie," or assembly, is made up of multiple layers that are intended to offer strength and resilience to weather. The structure usually starts from the bottom with a deck, which provides a stable base and is typically constructed of plywood or oriented strand board (OSB).

Insulation, which helps control the building’s temperature and energy efficiency, is an essential layer above the deck. Depending on the building code and climate, this layer may be made of spray foam insulation or stiff foam boards.

Next, in order to stop water intrusion into flat roofs, the waterproofing layer is crucial. Materials like built-up roofing (BUR), which consists of asphalt layers and reinforcing fabrics, or contemporary membranes like EPDM or TPO, which are renowned for their flexibility and durability, can be used for this layer.

Installing a protective layer or surface is often a vital step in safeguarding the waterproofing layer. This layer prolongs the roof’s life by protecting it from weathering, UV rays, and mechanical damage.

In urban environments and contemporary architecture, flat roofs are particularly advantageous because they create usable space and enable effective solar and HVAC installations. To ensure longevity and performance, however, careful consideration must be given to the materials and installation of each layer during construction.

Video on the topic

Diagnosis of flat roof. Opening a roof pie.

Flat roof: a roof pie. 5000 m2 roofs.

Pie of flat roofs

Flat roof for a frame house. Features and errors!

What do you think, which element is the most important for a reliable and durable roof?
Share to friends
Alexandra Fedorova

Journalist, author of articles on construction and repair. I will help you understand the complex issues related to the choice and installation of the roof.

Rate author
Add a comment