A drain for a flat roof: the specifics of the construction of internal and outdoor options

Effective drainage systems are necessary for flat roofs in order to avoid water accumulation, which can cause leaks and structural damage. Maintaining the integrity and lifespan of the roof requires an understanding of the specifics of drain construction.

For flat roofs, there are two main kinds of drains: internal and external. Inside the roof structure, internal drains are usually located close to the center or lowest point of the roof. They are made up of a drain basin that is connected to several pipes that carry water from the roof to the drainage system of the building.

In contrast, external drains are found around the edge of the roof. These drains gather rainwater and direct it away from the surface of the roof using scuppers or gutters. They are essential in keeping water from collecting on the roof and are frequently seen from the ground.

Every kind of drain has benefits and things to keep in mind. Because they can hide drainage systems from view and lessen the chance of damage or vandalism, internal drains are preferred. To guarantee adequate water flow and avoid debris clogging, they need to be carefully maintained.

Even though they are more noticeable, external drains are simpler to access for upkeep and inspection. In addition, they effectively remove water and can be combined with downspouts to divert water away from the foundation of the building.

Internal Drain Outdoor Drain
Installed inside the building on the flat roof. Installed on the outer edge of the roof.
Collects rainwater from the roof surface and channels it through pipes inside the building. Collects rainwater from the roof and directs it away from the building via downspouts or pipes.
Requires access for maintenance and cleaning. Designed to handle large volumes of water efficiently.
Helps prevent water pooling and potential roof damage. Often features grates or filters to prevent debris from entering the drainage system.

Distributions of flat roofs

The entire organization of the removal of rain and meltwater with a surface sensitive to their action is the goal of building a flat roof’s drainage system. She needs to function efficiently throughout the year to prevent the accumulation of ice, dust, and deciduous traffic jams.

The drain needs to take in and swiftly remove moisture from the sewer, rainwater collection, or ground, regardless of thermometer readings and precipitation amounts.

Classification of precipitation systems

You need to be precisely aware of the kind of system to use when arranging suburban property so that water can move freely and without hindrance:

  • External unorganized. Spontaneous drainage of atmospheric water. Used to arrange small household buildings with a height of not more than two floors.
  • External organized. Involving water collection using gutters or grooves, coupled with funnels, followed by transfer to the drainage pipeline. The system is laid on cornice overhangs and the outside of the load -bearing walls. It is used in the arrangement of residential and non -residential buildings, mainly low -rise, but the scheme is permissible for organizing drain from roofs with a height of up to five floors.
  • Interior. Water intake is carried out specifically for flat roofs with drainage funnels mounted in the roofing system. The water is drained by risers located inside the building.

In southern regions, where water in pipes freezes either very rarely or not at all during the cold season, outdoor emergency systems function flawlessly. In regions within the domestic temperate climate zone, external gutters are generally advised for roofs with rocky surfaces.

Due to the snow’s constant heating from the conventional warmth coming from inside, roofs without attics will have tangled snow for the entire winter. Meltwater will create ice congestion in cold pipelines.

It is possible to modify the snowmobile procedure if a flat roof has an attic. The temperature on the roof can be considerably lowered by opening hearing windows, which will cause the snow to melt considerably more slowly or not at all.

There is a risk of coating rupture in the northern areas during severe cooling. A stopper that keeps the current from building up on the water’s roof within the pipes. The volume of the crystallizing liquid increases dramatically, causing damage to the roof that absorbs it. Therefore, only non-residential buildings—that is, unheated buildings—have exterior drains in the northern and moderate domestic latitudes.

For example, cold warehouse structures have a side and a drainage riser installed on a remote railway plate. Such a structure’s impressive area aids in regulating the system’s and the environment’s temperature to prevent the formation of ice traffic jams.

Internal gutters are a feature of residential buildings with flat roofs located in the northern and moderate strip. Although the structure costs more, it functions consistently throughout the year. Because internal warmth keeps the risers inside the buildings warm all the time, ice buildup in pipelines is avoided. External gutters are the leading type in the southern latitudes.

Design components of drains

The external and internal gutter devices share a lot of similarities. Every system built for flat roofs consists of components that are similar in function and design, such as:

  • Water intake funnels and gutters, intended for receiving drains and transferring them to the drainage line.
  • Risers, providing at the reception points the maximum speed of the water current due to the gravity forces.
  • Distribution pipelines, required for the removal of atmospheric precipitation.

The drainage system’s primary landmarks are the highway’s minimum lengths connecting the water intake points and system unloading points. A riser with a gutter or funnel at the top and a short release at the base is part of the most affordable and compact external version.

Situated at a negligible angle, the release is 20 to 45 cm above the storm sewer or just above the blindfold that is shielded from blurry vision. Unfavorable conditions, such as the lack of a drainage system, poor soils, or an old foundation in an unfavorable water-neighborhood, frequently prevent such a plan from draining properly.

A ground or subterranean pipeline that leads to the most practical location for unloading is removed from the riser if the smallest line is laid, making it impossible to find alternative methods of draining water.

Since the system must undoubtedly move water outside the building, the pipeline diagram is used inextricably when building flat roofs with internal gutters.

The specifics of the formation of the slope

Slopes are formed in 1-2% to encourage independent water current in the required direction on flat roofs:

  • To organize the external type of drain, the entire plane must be tilted to the site of the water collection gutter installation. Most often it is the back wall of the building.
  • To organize water current according to the internal scheme, the slope is created to the place of installation of a water intake funnel. It is formed according to the convertible principle so that there is a decrease around each water intake in a radius of 50 cm.

Internal drainage systems’ water intakes can be placed not only in the middle of the roof but also close to the exterior wall, at least 60 centimeters away. As a result, there are numerous options in the tilt device’s convertible diagram.

Regardless, the inclined plane needs to face the water intake. Additionally, if multiple funnels are mounted on the roof, a sort of "watershed"—a tiny version of a mountain ridge—should be formed between them, with the slopes directing the water flow toward the closest funnel.

The issue of slope formation can be resolved using a number of tried-and-true techniques, including:

  • The tilting device during the construction process by installing the ceiling at the required angle.
  • Filling expanded clay in the form of a wedge-shaped layer followed by pouring cement-sand screed.
  • Organization of slope by laying the wedge -shaped mineral ward stoves.

Special tools are used to form the angle of metal structures and determine the slope of large-sized planes. They are rarely utilized in private construction.

Rules for the construction of internal drainage

Any constructed object should, of course, have its drainage system planned and calculated beforehand. The pipeline must be laid in the shortest possible route in advance, and the most practical location for its connection to a storm sewer must be considered.

Many types of flat roofing structures affect internal drain organizations. They are placed on roofs in the unexploded category and with and without attics. In light of the house’s planning requirements, an independent designer must consider that:

  • It is customary to have drafting risers in the area of ​​stairwells near the walls, columns, partitions. Preferably near residential premises for spontaneous heating in the cold periods of the year. Welding risers in the walls is strictly prohibited. Can be installed in strobes, mines, boxes. It is recommended to have them in the closet or similar utility compartments.
  • When organizing a drainage system of unheated construction, it is necessary to provide methods for artificial heating of funnels and risers. To increase the temperature of the external elements of the flat roof, an electric heating cable is installed or risers are mounted next to steam heating.
  • It is best to equip a flat roof with an attic with a pipeline passing within the attic space. It is performed in the form of a suspension network. To ensure the drain, horizontal sections of the pipes of the suspension system are set to include. For each linear meter, the pipes should have 5 mm lowering towards the water supply.
  • When laying the suspended pipelines, the drain section in the attic area needs to be insulated.
  • If the device of the suspension system is impossible, an underground laying of the pipeline is carried out. There are no regulations for the corner of the inclination of underground branches. The main thing is that the connection to the storm sewer is ensured. True, the underground scheme is much more expensive, significantly more inconveniently in terms of control and production of repair work. In addition, its implementation may prevent a too powerful foundation.
  • When designing, bends should be avoided if possible.
  • The riser at a distance of about a meter from the surface of the earth should be equipped with an audit for cleaning.

Actually, a drain with a flat roof ought to be set up similarly to a typical spillway system, complete with revisions, observation wells, etc. Pipes that can resist clogging are used in the construction of the suspended drainage pipeline, including those made of ceramic, plastic, cast iron, and asbestos cement.

Pipes made of the same materials are used to lay underground components; however, the hydrostatic regime is not necessary. Only production facilities exhibiting distinct vibration manifestations utilize steel long pipeline.

As per the technological specifications, a single water column can accommodate atmospheric drains with a roof area of up to 1200 m²; however, there must be a minimum of 60 m separating adjacent water receivers. I agree; the scale suggested for low-rise building is not very typical. To put it briefly, every tiny private home should have at least one funnel on its roof.

The quantity of water intake devices must be increased if:

  • Roof area exceeds the limits indicated by GOST.
  • The house is divided into sections. Then each compartment should be equipped with its own funnel.
  • Within one roof structure, there are elements separated by parapets, temperature or deformation seams. Each sector of such a roof should have two water intakes.

Water collection funnels are made for systems and combined buildings with attic space, as well as for flat roofs that are utilized and those that are not. Concrete floors coated in bitumen and their wooden counterparts covered in corrugated board are arranged according to certain models. Water receivers made of cast iron, ceramics, galvanized steel, and polymers are produced for all options utilized in the construction.

There are several sizes available for water intake devices. The funnel itself has wide sides, and the standard design consists of a removable cap with holes to allow water to flow through.

More sophisticated members of the roofing funnel class come with a removable glass, an umbrella to prevent clogs in the drain, and a clamping ring to secure the soft coating’s edges. Every model ought to give themselves the chance to clean and maintain.

All water intakes must meet the same standards, regardless of the funnel’s model or the building’s intended use:

  • The bowls of the water collectors are tightly attached to the coatings or the bearing flooring. For fixation, clamps are used in the amount of at least two pieces.
  • After installation, the funnel is obliged to ensure the tightness of the roof in the installation site.
  • The funnel pipes are connected to the risers using compensators, allowing to maintain the tightness of the joints when shrinking building structures.
  • The funnels are connected to the suspended systems.
  • The water intake bowl is installed below the level of the finish roof to exclude the likelihood of stagnation. The caps of water intakes on unexploited roofs in the plan have a rounded shape, usually they rise above the coating. The caps of funnels for operated roofs are installed on a coating, in plan they are most often square, so that it is easier to lay tiles around the device.

The use of thermal insulation is permitted in order to improve sealing and dependability in the region where the roof structure crosses. Single-level funnels are a feature of circular roofing systems.

Two-level water receivers are fitted with inversion systems and mechanically fastened roofs to collect water over waterproofing and vapor protection.

It is common practice to outfit water receivers on roofing structures coated with polymer membranes with a polymer clamp flange that is welded or adhered to the roof.

When installing a water intake device, this method provides the highest level of waterproofing possible. Water receiver gluing flange plexiglass needs to be reinforced with extra waterproofing layers. Replace the one that’s glued to the mastic with a glass chick.

The construction of the external drain

The southern regions are where external varieties of roof drains are constructed. It is advised to use their device in residential and office buildings in locations where there is only a small amount of precipitation—300 mm or less annually.

The following are examples of external rain and meltwater disposal systems:

  • Inorganized gutters recommended for device in arid areas. According to this scheme, the water is diverted by gravity by cornice overhangs.
  • An organized drain recommended for the equipment of non -residential buildings in northern and temperate latitudes, residential buildings in the southern regions with minor precipitation loss. The principle of operation lies in the systematized rainfall in the outer drainage funnel with the adjacent guide sides or to the gutter, followed by drainage of drains into storm sewers or to the ground.

Rags suggests a clever fix for the outdoor type system. The plan is to install a sandy filter after the water intake in the water supply network to clean the rainwater.

Containers are erected to remove the wastewater and collect the treated water. Consequently, the mechanism for linking the system to the sewage system has been eliminated. You can profitably address two issues at once with an intriguing plan: getting drinking-quality water and preventing water from standing on the flat roof.

A more pronounced cornice overhang is necessary for an unorganized drainage system. Galvanized roofing steel needs to pass over them before two layers of roller roof coating are applied on top. Overlapping layers are added one after the other.

The amplification’s width of 60 cm is the same as the recommended width for the flat roof’s lurns with disorganized drainage. Even so, the technical literature has more relaxed standards—at least 30 cm.

Enhancing by analogy the overhang of a mastic flat roof. Only mastic layers are applied, alternating with reinforcing layers of fiberglass or geotextile, in place of glued layers of bitumen or bitumen-polymer material. The primary layer of reinforcement is required to obstruct the cornice’s metal upholstery edge.

The conventional scheme is followed when attaching the external drain to the flat roof’s cornice. Many pre-made sets with thorough instructions for system assembly are available for purchase. Initially, brackets are fastened to the front board, where a gutter is easily installed, constructed from metal or plastic components.

A groove water funnel with a pipe installed in a convenient location for additional water transportation is where the riser is brought. Mounting brackets hold the pipe in place on the wall. The system is finished by installing a drain knee and covering its edges with plugs.

Selecting the appropriate drain for a flat roof is essential to preserving its structural soundness and efficiency. Depending on the particular requirements of your building, both internal and external drain options offer noteworthy benefits.

Installed directly into the roof structure, usually at its lowest point, internal drains allow water to pass through pipes and into the building’s drainage system. In addition to effectively removing water, this configuration maintains the roof’s aesthetic appeal by hiding any pipes from view from the outside.

Conversely, external drains are installed on the roof’s exterior, typically in close proximity to the corners or edges. They use gravity to move water into gutters or downspouts and away from the surface of the roof. This design is a popular choice for many flat roof applications because it is easier to install and maintain.

A number of considerations, including the location of the building, the design of the roof, and the local climate, should be taken into account when choosing between internal and external drains. Whatever the type of drain, effective water drainage and avoiding possible roof damage require regular inspections and proper maintenance.

Choosing the appropriate drain system is essential to protecting your flat roof from water buildup and extending its lifespan, regardless of whether you choose the covert operation of an external drain or the uncomplicated effectiveness of an internal one.

We examine the distinctive qualities of internal and external drain choices as we investigate flat roof drainage systems. Comprehending these structures is essential to guaranteeing efficient water management and long-lasting flat roofing. The main distinctions between external drains, which are installed on the roof surface, and internal drains, which are integrated into the roof structure, will be discussed in this article. We want to arm contractors and homeowners with the knowledge they need to choose the best drainage solution for their unique situation by looking at installation, functionality, and maintenance requirements.

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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.

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