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

Roof ventilation: recommendations for the calculation and design

Roofing materials reliably protect the structure from snow and rain, ensuring dryness and comfort in the interior. But the trick is that moisture attacks not only from the outside, but also from the inside. In the second case, it is possible to neutralize its negative impact only with the help of roof ventilation.

Content

• 1 Why do you need roof ventilation

• 2 Elements of roof ventilation

  2.1 Design features of aerators

• 3 Calculation of roof ventilation

• 4 Roof ventilation device

  • 4.1 Mansard roof ventilation

    • 4.1.1 Roof with waterproofing made of polymer vapor-tight foil
    • 4.1.2 Roofs with superdiffusion membrane as waterproofing
    • 4.1.3 Table: Height of the ventilation gap for different roof pitches (in cm)
    • 4.1.4 Video: ventilated ridge arrangement in the mansard roof
  • 4.2 Hip roof ventilation

• 5 Installation of the aerator on different roof coverings

  • 5.1 Installation of the aerator on metal tiles
  • 5.2 Installing the aerator on a soft tile roof
  • 5.3 Features of mounting the aerator on corrugated board

  • 5.4 Aerators for roofing from ondulin

    5.4.1 Video: installation of ventilation on ondulin

  • 5.5 Installation of ventilation elements on a folded roof

• 6 Installation of the ventilation outlet on the roof

  6.1 Video: installation of a ventilation outlet on the roof

• 7 Installation of the ridge aerator

  7.1 Video: Installation of the ridge aerator

Why do you need roof ventilation

There are two reasons to take care of the roof ventilation device:

1. Residential premises always contain a significant amount of water vapor, which is formed as a result of breathing and perspiration of residents and pets, cooking, hygiene and other processes associated with the use of water (washing, cleaning, dishwashing, etc.).
2. The roof covering is, by definition, impermeable to steam, so it cannot provide steam.

Without taking special measures, water vapor rising with warm air would condense on the inner surface of the cold roofing, with the subsequent occurrence of many negative processes:

• wooden structures, as a result of getting wet, would rot;
• a heat insulator, if mineral wool or other hygroscopic material is used in this capacity, it would be saturated with moisture, losing its thermal insulation properties;
• the roofing material itself would be damaged - either due to rust, if we are talking about a metal coating, or due to mold, if the roof is covered with ceramic tiles;

• in winter, water would form ice, destroying various elements of the roof and pipes, mines, etc.

  

  In the absence of ventilation in the attic space, the elements of the rafter system are overgrown with ice

To prevent all of these phenomena, roof ventilation is arranged, which implies the presence of a blown gap and ventilation of the attic space

The blown gap is called ventilation. The movement of outside air in this gap will carry all vapor penetrating to the coating outside. Along the way, it performs two more functions:

1. In the summer heat, it does not allow the heat from the heated roofing to penetrate into the attic space (especially important for attics).

2. In winter, it evenly distributes heat along the slope and thereby prevents the situation when, due to melting snow, water forms on one part of the roof, and on the other it freezes and turns into heavy ice and icicles.

   

   Air circulation in the under-roof space is provided by ventilation gaps on eaves, under the ridge and in dormer windows

The ventilation gap is arranged as follows:

• a waterproofing film is spread over the rafters;
• on top, along each rafter leg, a board with a thickness of about 30 mm is stuffed - a counter-lattice (it will fix the waterproofing film);
• a crate is packed on the counter-lattice across the rafters, and the roof covering is laid on it.

Thus, the required gap is obtained between the waterproofing film and the roof covering. Its height will be equal to the sum of the heights of the counter-lattice and the lathing, which is about 50 mm.

Various devices are used to ensure the movement of outdoor air in the ventilation gap, as well as to remove moist air from the attic.

Roof ventilation elements

The main elements of a roof ventilation system include:

1. Openings under the roof overhang, which are usually covered with so-called soffit gratings (protection from birds, insects and rodents), as well as along the ridge. These structural elements provide blowing of the under-roof gap due to wind and convection (when heated under the roof, the air rushes upward).

   

   The openings under the roof overhang are protected from rodents and birds by soffit gratings: they can be replaced with a filing with small gaps between the boards

2. Dormer windows. They are installed in gables and serve for ventilation of the attic space.

   

   The dormer is one of the important elements of roof ventilation.

3. Ventilation outlets. Just like aerators, they are pipe sections, but intended not for ventilation of the under-roof gap, but for connecting the exhaust ducts of general house ventilation to them or for ventilating the attic.

   

   You can connect an exhaust house system to the ventilation outlet or use it to ventilate the under-roof space

4. Aerators, also referred to as deflectors and weather vane. They cut into the roof covering at the ridge itself and serve to remove air from the under-roof space, that is, they perform the same function as the hole under the ridge. They are used in conditions where the thickness of the snow cover on the roof can exceed 2–3 cm (at low slopes), as a result of which the ventilation gap under the ridge would be drowned.

   

   The roofing aerator serves to remove air from the under-roof space when there is snow on the roof

Design features of aerators

There are two types of aerators available:

• point;
• linear or continuous (installed over the entire length of the ramp or ridge).

In addition, they also differ in the place of installation - they are ridge and pitched.

The aerator can be designed as:

• mushroom;
• shingles.

The aerator has a replaceable element - penetration, the design of which is selected taking into account the type of roofing

Aerators can be completed with a device for passing through the roof, adapted for a specific type of coverage

The product can be equipped with a fan - it is necessary to create forced draft in roofs with a low slope (convection manifests itself weakly in them due to the small height difference) or with complex outlines, where natural draft is not enough to overcome the aerodynamic resistance of kinks.

To prevent the ingress of precipitation and insects, the opening of the aerator is protected by a filter. The diameters of the aerators range from 63 to 110 mm.

Calculation of roof ventilation

The task of calculating ventilation is to determine the necessary parameters at which the volume of incoming air will be sufficient for effective steam removal.

1. For the outside air to enter the under-roof space, either a full-length slot 20–25 mm wide or a series of holes must be arranged in the soffit that hems the eaves overhang. The diameter of the holes depends on the slope of the roof:

   • up to 15 ^o - 25 mm;
   • over 15 ^o - 10 mm.
2. The total area of the inlets is determined at the rate of 200 mm ² per meter of length.
3. The ventilation gap under the roof covering must have a height of at least 50 mm.
4. The area of the outlet openings (under the ridge or in the aerators) should be 10-15% larger than the area of the inlets.
5. The total area of ventilation openings in the attic should be approximately 0.02–0.03% of the attic floor area.

6. Pitched aerators should be installed no further than 60 cm from the ridge. The optimal distance is 15 cm.

   

   Pitched aerators must be placed no further than 60 cm from the ridge

The height of the ventilation ducts above the roof is determined taking into account their proximity to the ridge or parapet:

• 1.5 m or closer - 0.5 m higher than the specified elements;
• between 1.5 and 3 m - flush with them;

• further 3 m - below the indicated elements, at the level of a conditional line drawn through them with an inclination of 10 ^o to the horizon.

  

  The height of the ventilation pipes depends on their distance to the ridge or parapet

Roof ventilation device

The roof ventilation system is arranged according to the type of roof.

Mansard roof ventilation

The roof of the attic is insulated. The layout of the ventilation gap in such a roof depends on what material is used as waterproofing.

Roof with waterproofing made of a polymer vapor-tight film

If the insulation is covered with a regular film that does not allow water or steam to pass through, ventilation gaps are arranged on both sides of it: from above - to the roofing and from below - between the film and the insulation. Due to the presence of a gap between the waterproofing and the insulation, it is excluded that the latter will get wet if moisture condenses on the film.

The lower and upper ventilation gaps must communicate in the area of the ridge, therefore, the waterproofing film is not brought to it by 5 cm

In order not to accidentally lay the heat insulator plates close to the waterproofing barrier, it is recommended to hammer the limiting nails into the rafters.

When using a simple waterproofing film, ventilation gaps must be provided on both sides.

Roof with superdiffusion membrane as waterproofing

Superdiffusion membrane is a polymer film in which microscopic conical holes are made. The membrane only allows steam to pass in one direction, so it is important to install it on the correct side. There is no need to make a gap under it - the insulation is placed close to the membrane.

The height of the ventilation gap in the attic roof depends on the angle of inclination of the ramp and its length.

Table: Height of the ventilation gap for different roof pitches (in cm)

Roof slope length, m	Roof slope
	10 °	15 °	20 °	25 °	30 °
five	five	five	five	five	five
ten	8	6	five	five	five
fifteen	ten	8	6	five	five
20	ten	ten	8	6	five
25	ten	ten	ten	8	6

Video: the device of a ventilated ridge in the attic roof

Hip roof ventilation

The hip roof differs from the usual gable roof in the absence of pediments, instead of which there are two triangular end slopes. The line of intersection of the end and longitudinal slopes is called a ridge. Roof ventilation is carried out according to the same principles as for a gable roof, while taking into account the following:

1. Ensure that air travels along the ridge to the ridge outlets.
2. If the roofing provides for the installation of a solid crate (plywood or board flooring), the counter-lattice in the ridge area is interrupted. Through the gap, air from the under-roof gap of the end slope will flow to the ridge. This solution leads to an increase in the span between the rafters. To compensate for it, additional slats are installed between the backbone and the counter-lattice.
3. You can also apply this technique: a gap is created in the crate, which plays the role of a backbone bar. In this case, the air flow will be able to move through the ridge into the ventilation gap of the adjacent slope and from there to the ridge or into the aerator.
4. To ensure the movement of air along the ridge, a cutout is made in the rafter leg with a length of about 20 cm and a depth equal to the thickness of the sheathing. At the same time, the strength remains sufficient, since such rafters are double, that is, their cross-sectional area is twice as large as conventional rafters.
5. Alternatively, you can attach an additional counter-lattice to the slant rafters parallel to the ridge, while ensuring sufficient clearance. It is necessary to wrap a waterproofing film on this block so that there is no overlap over the ridge, and then fix it. This technique ensures the movement of air in the lower ventilation gap.

6. To ensure the movement of air in the lower ventilation gap of the end slopes of the hip roof, in the places where the strips of the waterproofing film overlap, plastic gratings with sides are installed. Through them, air will flow into the upper gap and further into the outlets, and the water that appears on the film will flow around these gratings due to the sides they have.

   

   The main task of ventilation of a hip roof is to ensure air circulation along the ridge girder, for which a gap is usually made in the crate or counter-batten

Installation of the aerator on different roof coverings

Installation requirements for ventilation elements depend on the type of roofing material.

Installation of the aerator on metal tiles

Installation of an aerator or ventilation outlet on a roof covered with metal tiles is as follows:

1. On the roof, the installation sites of the aerators are marked. They should be no more than 60 cm from the ridge. The frequency of installation depends on the brand of the aerator and is indicated in its passport.

2. In the marked place, a template is applied to the coating (it is included in the kit), which must be circled with chalk or a marker.

   

   In order to outline the contours of the cut-out hole, use the template that is included in the aerator kit

3. The delineated section of the roof covering is cut out. Alternatively, you can first drill a series of small diameter holes along the contour, and then cut the gaps between them. This can be done with scissors for metal or a jigsaw.

   

   A through hole is cut along the drawn contour

4. The area of the coating adjacent to the resulting hole is cleaned of dirt and dust, and then treated with a degreasing compound.
5. A hole with a diameter 20% smaller than the diameter of the element pipe is cut in the casing (part from the aerator kit). Thus, the casing will be fitted on the pipe with an interference fit, so the connection will be tight.
6. The pipe is inserted into the casing, after which the complete assembly of the aerator is carried out.
7. The edges of the hole in the cover, on which the casing skirt will be installed, are lubricated with an outdoor sealant.

8. The fungus is installed in place, while the casing is screwed to the roof with self-tapping screws.

   

   The aerator cover is fixed to the crate from the outside and from the inside

9. The pipe is brought to a vertical position on the level and fixed. As a result, the deflector fixed on it should be at a height of at least 50 cm relative to the roof.

   

   The head of the aerator should rise 50 cm above the ridge

10. It remains to check the correctness of fastening all elements from the inside, that is, from the side of the attic. Found defects or distortions need to be corrected.

Installation of the aerator is not recommended in rainy weather

Installing an aerator on a soft tile roof

Basically, the process of installing a fungus aerator on a roof made of soft tiles looks the same as on metal tiles. The differences lie in some details. Here's what to do:

1. The outline of the hole is drawn using the template supplied.
2. A cut is made up to the waterproofing barrier.
3. The collected fungus is installed in the hole, the edges of which were previously coated with sealant. The casing is screwed on with self-tapping screws.

4. The casing is coated with bitumen and then pasted over with soft tiles.

   

   The aerator casing is attached to the lathing, and then a soft roof is laid on it

Features of mounting the aerator on corrugated board

To install the aerator on a roof covered with corrugated board, a wooden box is usually used. The installation process looks like this:

1. After applying the markings at the installation site of the aerator, a cross section is made in the corrugated board.
2. The resulting triangular petals are folded down and nailed to the rafters and other wooden elements.
3. According to the dimensions of the opening from the boards, a box is hammered together. Then it is wound up in the opening and screwed with screws to the elements of the rafter system.
4. A fungus aerator pipe is installed and fixed in the box, after which all the cracks are filled with sealant.

Ondulin roof aerators

Ondulin manufacturers produce all the elements necessary for both ventilation of the under-roof space and for organizing the exit to the roof of various ventilation ducts. Here is a list of them:

1. Aerators.

2. Insulated hood ventilation outlets. Exhaust ventilation ducts from the kitchen (the hood above the stove can also be connected here) and the bathroom are connected to such outputs. The pipe has a diameter of 125 mm and is equipped with a special coating inside, which prevents the formation of deposits of grease and dirt. Above the exit is equipped with a deflector that protects the inner cavity from precipitation and improves traction.

   

   Pipes for the outlet of ventilation of bathrooms and kitchen hoods are painted in the main colors of ondulin

3. Sewer ventilation outlets without insulation. Fan pipes of sewer risers are connected to such outlets. Without communication with the atmosphere in the sewer, during the salvo water discharge, a decrease in pressure will be observed, which can lead to the disruption of the siphons, followed by the penetration of unpleasant odors into the room. The diameter of the sewer outlet is 110 mm.

4. Insulated ventilation outlets. Such outlets differ from the previous version by the presence of a shell made of polyurethane or another polymer (thickness is 25 mm), which helps to reduce heat loss and thereby minimize the volume of condensation on the inner surface.

   

   The ventilation outlet for sewage can have a protective shell made of polymer material to reduce the amount of condensate formed

Corrugated pipes are usually used to connect ventilation outlets with corresponding ducts. The length of the outlet is 86 cm, and after installation, the length of the outer part, that is, the height of the outlet above the roof, is 48 cm.

Installation of ventilation outlets and aerators is performed as follows:

1. The place where the mounted element will be located, according to the usual scheme, is lined with ondulin sheets, with the exception of the side that faces the ridge.
2. Next, a special base sheet is laid at the exit point, in which there is an opening, fastening and a sealing casing for a ventilation outlet or aerator.

3. An element is being installed, which must be fixed for each wave.

   

   The pass-through element is installed on a laid sheet of ondulin with an overlap of 17 cm and is attached with special nails in each wave

4. Next, a regular sheet of ondulin is laid on the side of the ridge so that its lower edge lies on the base sheet with an overlap of 10 cm.

There are situations when it is not possible to use a base sheet with a ready-made opening and a sealing element. Then the opening in the coating is cut out independently, and the gap between its edges and the withdrawn pipe is sealed using the Enkryl waterproofing system, which is precisely designed to seal problem joints. It is applied as follows:

1. The area around the opening is treated with a degreasing agent.
2. Further, the first layer of Enkryl sealant is applied to it and to the pipe brought out into the opening with a brush.
3. The pipe or aerator is wrapped with a reinforcing cloth, for example, viscose Polyflexvlies Roll. Here it is necessary to pause - the sealant should saturate the fabric well.
4. The fabric wrapping is covered with a second layer of Enkryl, which is also applied with a brush.

This method of sealing the passage through the roof is designed for 10 years. After this period, the waterproofing will need to be renewed.

To seal joints and cracks, instead of fabric and paste-like sealant, you can use Onduflesh-Super adhesive tape.

Video: installation of ventilation on ondulin

youtube.com/watch?v=khl02P01Sag

Installation of ventilation elements on a folded roof

For installation of elements of roof ventilation on a folded roof (covering is made of metal sheets), it is best to use a universal seal for roofing passages. It consists of a square aluminum flange on a silicone lining and attached to it a stepped pyramid made of the same silicone or special rubber resistant to ultraviolet and other weathering. The size of the seal must be selected so that the inner diameter of the pyramid is approximately 20% less than the outer diameter of the aerator or ventilation outlet.

Installation is carried out as follows:

1. An opening is cut in the roof covering according to the inner dimension of the flange.
2. The pipe (ventilation outlet or aerator) is threaded into a universal seal. With a diameter difference of 20%, the pipe enters rather tightly, so it makes sense to lubricate it with shampoo or soapy water.
3. The edges of the opening cut in the seam roof are coated with a sealant for outdoor use.
4. The ventilation element with the seal put on it is installed in the opening, while the flange is tightly pressed against its edges.

5. The flange of the seal is screwed to the roof covering with self-tapping screws with a pitch of 35 mm.

   

   The sequence of work on installing an aerator on a folded roof repeats a similar process for metal tiles or corrugated board

Installation of a ventilation outlet on the roof

In the place where there is a ventilation outlet to the roof, a so-called passage assembly is installed, the main task of which is to seal the gap between the pipe and the roof covering. Nodes can be very different both structurally and in appearance. Basically, the following types are distinguished:

1. Equipped with and without a valve: the presence of a valve allows you to regulate the movement of air in the ventilation system. Passage nodes equipped with this element are installed mainly on the roofs of administrative and industrial buildings. Units without a valve do not provide for adjustment, but they are cheaper.
2. With or without insulation: the first in their design have a layer of mineral wool (this insulation is non-combustible) and are used in regions with cold climates. The presence of thermal insulation prevents moisture condensation on the internal surfaces of the unit.
3. With manual (mechanical) and automatic control: in the first case, the user moves the shutter to one position or another by pulling the cable attached to it. In the second, the damper is driven by a servo driven by an electronic controller. Such a system with the help of appropriate sensors can analyze the temperature and humidity in the room and, taking these indicators into account, regulate the throughput of the ventilation ducts.

The section of the knot can be rectangular, round and oval. When choosing this element, the following microclimate parameters are taken into account:

• relative humidity;
• the content of dust and chemical contaminants in the air (gas content);
• temperature differences in the room.

The ventilation outlet is installed in the same way as the aerator, with the only difference that it must be carried out not only through the roof covering, but also through the waterproofing and vapor barrier films. To do this, proceed as follows:

1. A cruciform incision is made in the films.
2. The ventilation outlet pipe is inserted into the formed opening.

3. The triangular petals in the places where the films are cut are pressed against the pipe and fixed with adhesive tape. In this case, the petals of the waterproofing film should be bent up, and the vapor barrier - down.

   

   Some ventilation elements have a special element - a hydro-barrier, which is attached from the inside and fixes the cut edges of the insulating films to the crate

Video: installation of a ventilation outlet on the roof

Installation of a ridge aerator

Ridge aerators can be of different designs, but in most cases, the installation is done as follows:

1. The old covering is dismantled from the ridge area (if the roof is new, you should skip this point of the instructions).
2. If a continuous crate is laid under the covering, a line is drawn on it parallel to the ridge, at a distance of 13 mm from it (on both slopes).

3. A cut is made along the drawn lines with a circular saw, with an indent of 300 mm from the outer walls.

   

   The ventilation cut is made on both sides along the entire length of the roof, not reaching 30 cm to the gables

4. Two ridge shingles are attached at the edges of the roof.
5. Roof aerators are bent to the desired angle, depending on the angle of inclination of the roof.
6. Aerators are installed overlapping in place. During installation, it must be borne in mind that the covering and the covered ends are structurally different. There is no need to seal the overlap. The baffles of the aerators must lie on the floor. If this rule is not followed, water can flow under the roof.

7. Aerators are attached with nails that need to be driven into specially made holes. The sides in the process of hammering in nails must be alternated.

   

   The ridge aerator is attached with nails through special holes

8. The last aerator is cut to length with a 13 mm margin. Its edges are superimposed on the previous part.

9. The roof covering is laid, which must be fixed with nails or self-tapping screws. It is necessary to drive or screw the fasteners into the specially marked area on the ridge aerator. It is marked as follows: "roofing fixation zone".

   

   The ridge aerator is covered with roofing material, which is attached through specially marked holes

10. The places where the ends of the chain of aerators are adjacent to the roof are sealed with a special mastic, which is usually supplied with the aerator. To do this, you need to prepare an assembly gun.

Video: installation of a ridge aerator

In no case should you neglect the roof ventilation device. There are no elements in the roof structure, except perhaps for films that would be immune to the negative effects of moisture, and in the absence of high-quality ventilation, it will certainly appear. By following the recommendations outlined in this article, you will ensure a long service life of the roof and a comfortable microclimate not only in the attic, but also in the rest of the house.