Metal Roof Ventilation, Its Elements And Purpose, As Well As How To Correctly Calculate And Organize

2024 Author: Bailey Albertson | [email protected]. Last modified: 2023-12-17 12:53

Metal roof ventilation

Metal tiles are one of the most common roofing materials. Its popularity is due to its reasonable price, ease of installation, low weight and variety of shapes. However, just like corrugated boarding and seam roofing, metal tiles are afraid of condensation settling on the inside of the roof. The appearance of moisture leads to premature destruction of the anti-corrosion coating and the formation of rust on the metal surface. To prevent the development of these processes, special technologies have been developed that exclude the formation of condensation and extend the service life of the metal roof to 45-50 years.

Content

• 1 Elements of ventilation of a roof made of metal

• 2 Calculation of ventilation of metal roofing

  2.1 Table: height of the ventilation duct depending on the slope of the roof

• 3 Ventilation device for metal roofing

• 4 Installation of ventilation of a metal roof

  • 4.1 Installation of aerators

    • 4.1.1 Video: installing an aerator in a metal roof
    • 4.1.2 Video: Dormers on a hip roof

  • 4.2 Installing a ventilated ridge

    4.2.1 Video: installing a ridge on a metal tile

  • 4.3 Installation of the ventilation grill on the cornice

    4.3.1 Video: installing spotlights

  • 4.4 Ventilation of a cold metal roof

  • 4.5 Ventilation of a warm metal roof

    4.5.1 Video: Five Elements of Proper Roof Ventilation

  • 4.6 Recommendations for roofers for ventilation installation

Roof ventilation elements made of metal tiles

Ventilation is an integral part of a modern roof. This is a simple and inexpensive system, which is essentially a pipe that removes water vapor, which saves the roofing from destruction under the influence of temperature drops and excessive moisture. But it protects not only the roof. Wooden structural elements also suffer from getting wet: rafters, battens, cornices, etc., as well as insulation.

Excess moisture leads to the destruction of the structure of wooden structures

The high-risk zone is the exit of ventilation and sewer shafts to the attic and to the roof surface

All of these problems are solved by arranging thoughtful ventilation, which is of two types.

1. Natural ventilation (or draft) occurs inside a closed system (pipes, mines, etc.) at a differential pressure or air temperature. Examples of devices operating on the principle of natural ventilation surround us from all sides. These are chimneys, ventilation shafts and the like.

   

   Thanks to natural circulation, uniform heating and renewal of indoor air occurs

2. Forced ventilation is an artificially created movement of air masses in the desired direction. Formed by fans, compressors and air duct systems. A good example of forced ventilation is air conditioning systems in residential and industrial premises.

   

   Forced ventilation includes a duct system and power units for pumping air

The overwhelming majority of roof ventilation devices operate on the basis of natural air movement. They do not require electricity or maintenance, and steam is removed automatically in accordance with the laws of physics.

The general name for the mechanisms that serve to ventilate the under-roof space and remove wet vapors are roof aerators. The word comes from the English "aerate" - to rotate the air. It entered construction terminology in the middle of the last century, when devices were installed on flat roofs of high-rise buildings to extract exhaust air and prevent the roof from swelling during sudden temperature changes.

Aerators are installed at the joints of floor slabs and on elevations of the roof

Today, for each type of roof, separate models of aerators are produced, which take into account the size and configuration of the roofing material. The device is a molded plastic (polypropylene) product that is resistant to acids, weather conditions and ultraviolet radiation. It is able to function at temperatures from -50 to +90 ^o C and withstand short-term exposure to fire.

The size and shape of the aerator is selected depending on the roof area and the type of roofing

There are also metal deflectors - 316 AISI stainless steel. The relatively high price does not allow widespread use of these products in private housing construction. Therefore, metal aerators are usually used only in industrial facilities.

Metal aerators are quite expensive, so individual developers hardly use them.

Calculation of ventilation of metal roofing

In order to choose the right ventilation equipment for a roof made of metal tiles, it is necessary to build on the following parameters:

• roof area;
• roof shape;
• the angle of inclination of the slopes;
• aerator performance.

It is believed that metal roofing is most vulnerable to moisture and needs maximum protection from fumes rising from the building. Therefore, such a roof is equipped with the maximum number of devices, including forced ventilation systems. Every builder knows that there are no restrictions on ventilation. Ideally, the air temperature both outside and inside the roof should be the same, and this is achieved only by active ventilation.

There are no government standards for installing pitched roof aerators, so there is often disagreement over the frequency of their location. Some believe that it is necessary to mount deflectors at the rate of one device per 40 m ^{2 of the} roof, others argue that this is not enough and it is necessary to double their density. Someone prefers to put the devices dotted with a step of 0.5–0.6 m, there are even experts who advise cutting the valve into almost every sheet. Perhaps their opinion is dictated by the desire to protect the roof, but it can also be assumed that this is just an attempt to increase the cost of the goods and services provided.

The main regulatory document governing the construction of the roof is SP 17.13330.2011. Appendix B provides several examples for calculating the number of ventilation devices (aerators). Complex mathematical calculations, taking into account many factors (climatic conditions and material properties), given in the document, are for informational and advisory purposes. All calculations are for flat roofs. Regarding a pitched metal roof, it is noted that the ratio of the area of the ventilation ducts to the area of the horizontal projection of the roof should be 1/300, and a table is given of the recommended height of the ventilation duct depending on the angle of inclination of the roof.

Table: height of the ventilation duct depending on the slope of the roof

Roof slope, degrees (%)	Height of the ventilation duct for removing vaporous moisture, mm	Height of the ventilation duct for removing vaporous and building moisture, mm	The size of the ventilation duct inlet	The size of the outlets of the ventilation duct
<5 (9)	100	250	1/100	1/200
5-25 (9 -47)	60	150	1/200	1/400
25–45 (47–100)	40	100	1/300	1/600
> 45 (100)	40	50	1/400	1/800

The frequency of the location of the air outlet pipes is determined in each case individually at the discretion of the roofer

There are also several notes in the above document.

1. The height of the ventilation duct is taken for a slope length of no more than 10 m; with a longer slope length, the duct height is increased by 10% per meter, or it is additionally provided for the installation of exhaust devices (aeration pipes).
2. The minimum size of the channel inlet openings (in the cornice section) is 200 cm ² / m.
3. The minimum size of the channel outlets (on the ridge) is 100 cm ² / m.

In practice, this means that when calculating the roof ventilation system, you need to build on the size of the horizontal projection area. With a small error, the projection area can be considered the floor area of the attic space.

For example, there is a pitched roof metallocherepichnoy located at 45 ^on. The size of the attic space is 8 × 6 m. All necessary coefficients are taken from the third row of the table.

1. The total area of the inlet ventilation ducts located on the eaves must be at least 6 8/300 = 0.16 m ².
2. The area of the outgoing channels located on the ridge of the roof should be at least 48/600 = 0.08 m ².
3. The height of the ventilation duct located directly between the tiles and the waterproofing foil must be 40 mm. Structurally, this means that the counter-lattice must be mounted from a bar with a thickness of 40-50 mm.

The size of the counter-lathing beam determines the height of the ventilation duct between the roofing and waterproofing

In fact, much depends on the objective conditions, climatic zone and landscape, prevalence of winds or rains, maximum and minimum temperatures in the average annual weather calendar. The right decision would be to listen to the opinion of independent experts, whose assessments are tied to practical experience in a particular region. It is also useful to study the recommendations of the manufacturers, which in the accompanying documents give the technical characteristics of the product.

And finally, there is another method that has been worked out in practice. This is the observation and assessment of the condition of the inner surface of the roof during operation. The picture becomes especially clear in the off-season, when cold air fronts appear. If during this period abundant condensation forms on the metal, additional measures are definitely needed to remove moisture and ventilation. Fortunately, aerators are installed at any time of the year, regardless of the air temperature. Of course, this method is applicable only to a cold roof, since it will not be possible to observe the condition of the inner surface of the metal coating through the mounted roofing carpet.

Carrying out a regular inspection of the roof from the inside will help determine the installation of additional ventilation devices

Metal roof ventilation device

The roof ventilation system consists of the following structural elements:

• cornice vents;
• ventilated ridge;
• roofing aerators;
• groove.

Let's consider each of the devices in more detail.

1. Cornice duct. Another name is a ventilation entrance, since air is drawn in through the slots and holes in the strip under the eaves, which then enters the under-roof space. Distinguish:

   • point vents. Holes with a diameter of 10 to 25 mm at the bottom of the cornice. The smaller the slope of the roof, the more airflows are made. As a rule, the holes are located under the gutters to avoid icing, and are lined with soffits on the outside to protect them from clogging with leaves or debris;

     

     Fine mesh screens prevent air vents from clogging

   • slotted vents. Holes in the form of vertical or horizontal slits up to 2.5 cm in size. Provide round-the-clock access of fresh air to the under-roof space. In order to prevent leaves and small debris from clogging the cracks, an additional ventilation mesh is mounted on top of the air vent, consisting of a fine-mesh braid.

     

     When installing the cornices in the lower part, they leave gaps for air intake

2. Ventilated ridge (or ridge vents). Another common name is a ventilation outlet. Since the ridge is the upper point of the pitched roof, it is here that the air comes out. It is produced in two ready-made versions: with slit-shaped air vents (up to 50 mm) or with point holes along the entire length of the ridge.

   

   One of the options for the device of a ventilated ridge for a metal roof is the organization of a slot-like air in the entire length of the slope; the same material is used to cover it as for the main part of the roof

3. Roofing aerators. They are additional components of the general roof ventilation system. With the help of aerators, the movement of air masses is enhanced, giving it the desired direction. The structure is a small pipe (up to 50 cm), inside of which there is a passage that ensures the tightness of the connection with the roof, and a deflector - a cap to protect against water and dirt. Installation is carried out both during the initial assembly of the roof and on an already in use roof. The versatility of aerators lies in the fact that they are used for all types of roofs and coverings, from metal to soft bituminous roofing. Each company engaged in the production of roofing material produces aerators for its own products. The assortment includes up to 50 items of various shapes and sizes.

   

   The shape and color of the aerator is matched to the specific type of roofing material

4. Gutters are a ventilation element that serves a complex roof. If a depression (valley) is formed at the junction of the slopes, then before laying the metal tile, it is necessary to install a groove, which will create a ventilation channel for air movement. Gutters are of two types: internal and external.

   

   The rules for installing valleys involve the creation of ventilation ducts along the entire length of the device.

We looked at passive methods for removing moisture. Most often, they do an excellent job with the task. But if such ventilation is not enough, forced air circulation systems are used. Their main difference lies in the presence of an electric fan, which is located inside the pipe and accelerates the passage of air.

Air speed control can be carried out automatically or manually from a special operator panel

In addition, there is a group of so-called turbine-type aerators. Many experts consider them to be the most effective roof ventilation devices. The upper part of the device, interacting with the external environment, is equipped with a deflector with a turbine, which rotates under the influence of the wind. In this case, the natural thrust increases many times (5-7 times depending on the strength of the wind). A prerequisite for the use of such equipment is an adequate increase in the size of the eaves and soffits.

The turbine built into the pipe increases the efficiency of the aerator several times

When choosing a set for ventilation of a roof made of metal tiles, you need to pay attention to the following points:

• you should purchase an aerator with a base profile that matches the relief of the tiles;
• the package must include the following elements - a list of technical characteristics of the device, an installation and operation manual, a mounting template, gaskets, a pass-through element, a set of fasteners;
• the color of the aerator should be matched to the color of the metal tile;
• the larger the size of the serviced area, the larger the diameter of the aerator (small sections can be equipped with pipes with a small diameter);
• the material of the product must correspond to the conditions in which the device is used (the quality of plastic or metal must be documented).

Installation of roof ventilation from metal tiles

The main ventilation elements are mounted at the stage of roofing assembly. These include cornice vents and a ventilated ridge. The gutters are installed simultaneously with the installation of the valley. Air gaps are left around the entire perimeter of the eaves and ridge.

Aerators are mounted after the completion of the metal tile laying. You can install them yourself using a simple tool.

Installation of aerators

Installation of the aerator is carried out in several stages.

1. The shape of the hole is drawn on the roof using the template included in the kit.

   

   The hole cutout template is included with the aerator

2. The metal is cut with an electric drill and jigsaw. The hole must reach the depth of the heat-insulating layer.

   

   The pipe (passage) of the aerator must be lowered to the thermal insulation mats

3. If during installation a damp insulation is found, it must be replaced.
4. The lower part of the pipe is treated with bitumen mastic and pressed against the base of the roof.

5. The skirt of the branch pipe and the protective cover are fixed with self-tapping screws.

   

   Self-tapping screws included in the kit are used to fix the aerator.

6. Before fixing, the sole of the aerator is treated with a silicone sealant to prevent leakage.

Video: installing an aerator in a metal roof

Video: dormer windows on a hip roof

Installing a ventilated ridge

The ridge for metal roofing has several varieties. But regardless of this, the installation is carried out according to a single algorithm.

1. Before installation, a polyethylene or polyurethane seal is inserted into the ridge.

   

   The seal protects the inside of the ridge from moisture and dirt and is shaped like a tile

2. The first element with an end cap is installed. Fastening is carried out with special screws with rubber washers.

   

   To avoid leaks, the self-tapping screws must be tightened strictly perpendicularly, not overtightening, but also without loosening the attachment point unnecessarily

3. The next section is laid on the previous one with an overlap of 10 cm. It is fixed in the same way.

   

   Regardless of the type and shape, the ridge strips are stacked sequentially with an overlap of 10 cm

4. After passing the entire length of the ridge girder, the last section is locked with a protective plug from the outer end.

When installing a ridge on a metal tile, it is necessary to use safety equipment, use reliable ladders and stable trestles. It is recommended to tie the screwdriver to the belt with a small cord of 1–1.5 m.

Video: installing a skate on a metal tile

Installation of a ventilation grill on the cornice

Many builders use natural gaps between the boards when arranging ventilation. But over time, the boards can swell, and the gaps can decrease in size. Therefore, it is more reasonable to install ready-made metal or plastic ventilation grilles on the eaves.

The installation procedure is very simple.

1. Use a pencil or marker to mark the installation site.

   

   To ensure the evenness of the marking, use a construction cord

2. A hole is cut or a guide profile is mounted (depending on the grille design).

3. The grill is attached.

   

   The grille consists of perforated holes with a predetermined flow rate

When using ready-made soffits instead of ventilation grilles, installation takes place using guide profiles.

Video: installing spotlights

Cold roof ventilation made of metal

The arrangement of ventilation in a cold attic is within the power of everyone who has theoretical knowledge and simple practical skills. Since the under-roof space is adjacent to a large volume of air in the attic and the circulation is not obstructed, moisture does not condense. Air circulation is freely carried out through eaves, skylights, ridge and roof ridges.

Humid air currents accompanying human life rise to the roof

When equipped with ventilation of a gable roof, the air flow is carried out through a wooden filing in the eaves or holes in the pediments. If the gables are stone (brick or block), it is advisable to arrange openings for the flow of fresh air in the form of opening window-type windows.

Ventilation grilles are installed in gables or eaves

There are no gables in the design of the four-pitched hip roof, so the role of the air intake is played by cornice overhangs, in which holes of the required size (from 5 to 10 mm) are left. The air is discharged through a ventilated ridge girder. If the cornices are sheathed with plastic soffits, then the air enters the attic through the perforated holes.

The main condition for installing an uninsulated roof is compliance with ventilation standards: the size of the incoming (outgoing) air vents and the height of the ventilation gap between the crate and the metal covering

Hip roof ventilation is a classic pattern of air movement from eaves and dormers to the ridge and aerators

One of the problem areas of the pitched roof is the gutter. Ventilation in the valleys is difficult, especially in winter when snow accumulates there. To solve this issue, point aerators with a height of more than 0.5 m are installed along the gutters. But the most effective is the use of forced ventilation - inertial turbines or electric fans.

Ventilation of a warm metal roof

An insulated roof differs from a cold one in that a carpet of heat-insulating material is located between the roof and the attic, protected on both sides by waterproofing and vapor barrier films. In principle, if the roofing cake is assembled efficiently, then the metal is reliably protected from heating and fumes from below.

In the insulated roof, air is taken in through the eaves, and the exit through a ventilated ridge

When installing metal tiles, it is necessary to use a two-level lathing, which forms a technological gap for free movement of air inside the roof. The minimum gap size is 40-50 mm.

If mineral wool or basalt wool is used as insulation, it should be remembered that in the first few days after unpacking, the mats or rolls increase in volume by 15-25%. Therefore, it is best to install the vapor barrier after this period, after waiting for the heat insulator to take its natural form.

The vapor barrier is sealed over the mineral wool mats

The classic ventilation scheme in insulated roofs remains the same. Air is drawn in through the eaves and expelled out of the ventilated ridge. Insulation only contributes to the work of natural ventilation, but the requirements for the tightness of thermal insulation are very high. All layers are overlapped with gluing the joints with construction tape. In complex roofs, diffusion membranes are used, which allow vapors to pass in only one direction and are mounted directly on the heat-insulating carpet.

The waterproofing membrane is attached to the rafters with a stapler, and then finally fixed with counter-lattice bars

There are no technological features in the installation of ventilation for roofs with different shapes. In shed, gable, hip and hip roofs, the ventilation principles are the same. Only the complexity of installation and the number of installed devices are changing.

Video: five elements of proper roof ventilation

Roofers recommendations for ventilation installation

Any business has its own subtleties. Experienced craftsmen advise paying attention to the following points when installing ventilation.

1. Dust penetrating the ventilation gaps has a certain level of hygroscopicity. Large accumulations can cause moisture to the heat insulator.
2. The area of the ventilation ducts should not be less than 450–500 cm ² at any point. The gap height is not less than 45-50 mm.
3. The air must be protected from foliage, grass, birds and insects. To do this, use additional mesh filters and grates.
4. With a roof length of more than 10 running meters, it is recommended to use aerators and deflectors.

When building a new or restoring an old roof, you should not neglect the ventilation device. High-quality removal of water vapor from the surface of the metal roofing makes the roof practically invulnerable. Conversely, unreasonable savings translate into shorter roof life and premature metal corrosion.