All roofs for houses can be divided according to configuration into: flat, pitched. Flat, have a flat roof with an inclination angle of 3-5 degrees. These days they are used extremely rarely, since water stagnation often occurs in them. This type of roof installation is suitable exclusively for outbuildings, as well as for small baths.
In turn, pitched roofs are used much more often. They, in turn, are divided into:
- (pincer);
- semi-hip gable;
- semi-hip hipped;
- multi-pincer (multifaceted).
The most popular among the above are single- and double-pitched roofs, which are often also called “cold” and “warm” due to the design of the rafter system and the roofing pie.
Cold roof construction technology
It can only be used in cases where the room has the necessary thermal insulation, including from the ceiling adjacent to the attic, or if a small room is being built.
The main difference between a “cold” roof is that it is installed directly against the wall of the house. That is, the main load will not go to the rafters, but to the room. The beams will directly support the roof, so their thickness can be adjusted from 5 centimeters or more.
The rafters are supported on the Mauerlat. Purlins, struts, racks and beams, in most cases, are not equipped, since even ordinary crossbars are quite enough to reliably hold the shape of the roof and prevent it from being beveled later during operation (due to wind and rain). The ridge purlin rests directly on the rafter legs.
A roofing pie for a “cold” roof consists of one level of sheathing, an external roof (which can be tiles, slate), vapor and waterproofing. There is no insulation layer provided, since the attic of a cold roof is not intended for use as a living space.
However, thanks to a properly designed ventilation system, the temperature inside the roof attic is 5-10 degrees higher than the environment. Thermal insulation is attached to the floor of the attic, which protects the interior space of the living part of the house from cold air. Ventilation pipes are also installed here and a vapor barrier membrane is laid, which protects the house from condensation.
The construction of a cold roof is simple, so it is suitable for the construction of summer kitchens, closed gazebos, and the construction of modular block containers (which are initially insulated).
For more information on installing a cold roof under metal tiles, watch the video.
Arrangement of a warm roof rafter system
The rafter system for warm roofs is somewhat more complicated, since it involves using the attic as a living space. The best option for this type of roof is an attic system, which allows you to get a fairly large amount of free space. The structure of the roofing pie in this case looks like this:
- roof;
- sheathing and counter-lattice;
- steam and waterproofing;
- thermal insulation (mineral wool or polystyrene foam board);
- decorative layer (interior finishing).
The main difference between the design of the rafter system is that it is supported by supporting
beams, as well as mauerlat. Additionally, the roof is divided into purlins and struts (for gable systems). The angle of inclination of such roofs, as a rule, is divided into two parts: at first it is about 120 degrees, then (after the last support beam) - about 35.
A fairly well-known technology for arranging roofs is the system with layered rafters. But today it is rarely used, since it requires a large amount of wood materials, although it does not make it possible to equip a full-fledged living space in the attic.
The undeniable advantages of this technology include: high-quality load distribution, adjustable roof height (the angle can easily be changed during construction). But still, roof structures with hanging rafters are much more often used.
Also in the rafter systems of warm roofs there is a so-called “wind beam”, which is responsible for the stability of the roof. The side rafter legs, as a rule, are lengthened due to wooden “fillies”, to which it is convenient to subsequently install drainage systems.
Installation of the central beam is carried out in cases where the running length of the roof is more than 7 meters. If the length is shorter, the decision should be made depending on the load on the ridge span. If it turns out to be too high, this will lead to the penetration of additional moisture and condensation into the interior of the attic, which, of course, must be avoided.
Sheathing and reinforcement strips
Counter-lattice is an additional layer of thin rafters that are used in warm roofs for installing internal thermal insulation. This type of lathing can also be attached directly to retaining strips if they are provided for in the overall design.
Installation of reinforcement strips begins with the installation of the upper retaining beam. A mauerlat is laid along the perimeter of the roof, which is tightened with ties (the beams are laid directly on the roof and secured with solid staples or studs). The fastening of the retaining strips to the main beams is carried out through metal corners (tightened with 4-6 self-tapping screws).
Roof insulation and waterproofing
Mineral wool reinforcing mesh or simple polyethylene film is used as waterproofing for warm roofs. In some cases, it is recommended to install it in two layers: above the thermal insulation and below the thermal insulation. It should be borne in mind that this option is only possible in cases where a basalt mat that is resistant to moisture is used as insulation.
It is important to note one more point: waterproofing will reliably protect the roof from condensation only if it is laid between the sheathing and the counter-lattice. At the same time, it is most convenient and reliable to install the heat-insulating layer directly on the internal beams (laying the mats vertically between them). But it is also possible in two layers, while the inner layer must be installed horizontally (depending on how the counter-lattice was installed).
In most cases, installation of sound insulation is not necessary, but if you decide to use it, then it is recommended to lay a layer behind the insulation before interior finishing (plasterboard).
Roof ventilation system
The roof ventilation system can be configured in two ways. The first one is suitable if you do not intend to use the attic for living. It is most rational to arrange traditional natural ventilation through side slopes. But keep in mind that if a warm chimney passes through the attic, cold air will accumulate in the lower part of the room. If internal ventilation is simply exhausted through the attic, cold air, as well as condensation, will form directly under the roof.
In warm roof systems, as a rule, artificial ventilation of the room is provided. Its performance is calculated based on the volume of the attic divided by 3 or 4. This system is necessary in any case, since an anti-condensation membrane is additionally installed in such roofs. And it significantly worsens the air exchange between the external and internal environment.
Instructions for laying metal tiles
It begins with the installation of the eaves strip, lower valley, and adjacent panels. Then the sheets of metal tiles themselves are laid along the rafters, which are attached to the wood base using self-tapping screws (roofing fasteners are used) and ends with the installation of the ridge element, upper valley and end strip.
For more information about editing and its main mistakes, watch the video.
The cost of installing metal tiles depends on the complexity of the work (the height of the roof, the angles of inclination) and whether it is insulated or not. On average in Moscow, the price for installation will cost 400-450 rubles per sq.m., if insulation is necessary, then the cost increases by 70 rubles per sq.m. for each layer (50 mm.). Often, in addition to installation, it is necessary to dismantle the old roof, and this adds to the cost of about 100 rubles. per sq.m.
Completion of roofing work
Work on arranging the roof and roofing ends with removing the roof from unnecessary elements: sticks, tools, sawdust, shavings, etc. It is necessary to paint the metal tiles in the areas where trimming and cutting them with paint in the color of the roof - to prevent metal corrosion.
If the interior decoration of the attic is intended, it is most convenient to use plasterboard or plywood board. In order for the inner decorative layer to be absolutely smooth and even, it should be mounted on aluminum profiles (they are also attached to the counter-lattice using corners and belts). After this, you can begin installing gutters around the perimeter of the roof.
At the moment, in the process of constructing a country residential building, different options for high-quality modern structures for the roofing part of a building or structure can be used. A relatively simple one among them is the cold roof. Such a device is optimally suited in cases where the common attic space is not used as a residential space for some reason.
The design scheme of such a plan is characterized by simplicity; there are elements such as high-quality waterproofing, load-bearing elements and roofing. There are some installation features of this design. They consist in the fact that it is imperative to provide a high-quality ventilation gap designed to remove accumulated condensate.
This is necessary so that the load-bearing structural elements, as well as the roofing itself, are effectively protected from the adverse effects of moisture.
The installation of such a roof itself is not characterized by any difficulties. The most important thing that needs to be done is to properly fasten all the profiled metal sheets present.
This must be done so that precipitation cannot penetrate through the numerous joints under its surface. Before starting the construction process, it is worth carrying out such important steps as:
- Make all necessary calculations;
- It is imperative to calculate the parameters of the angle of inclination of the roof structure;
- It is important to determine the pitch of the sheathing;
- You also need to decide on the method of fastening sheets of roofing material.
Compliance with these rules will allow the construction process to be completed quickly and efficiently.
The one described differs from the warm roof in its relative simplicity. The only thing that must be taken into account is the special type of roofing material and its flooring.
When using modern metal tiles, it is recommended to provide an effective ventilation gap that will properly remove condensation from the room located under the roof. This is necessary so that the steel element is not subject to corrosive destructive processes.
The device of this design is the installation of a rafter system; a membrane or high-quality film is mounted on it. Then the counter-lattice, sheathing, and also the covering, that is, metal tiles, are secured.
The main features of this design include the complete absence of a heat-insulating layer; there are also special ventilation holes, they are located strictly under the ridge and on all slopes without exception.
These devices are used for efficient removal of water. The process of professional design and subsequent installation will not present any difficulties for the master; the most important thing is to correctly carry out all the calculations.
The process of high-quality and professional installation itself consists of such features as:
- If you are planning a device, you will need to competently select a high-quality protective membrane for effective protection from excess moisture. For an attic room, only special high-quality waterproofing can be suitable, which can take the form of an ordinary membrane, which is usually made from PVC.
- If you do not need to use the room in the future, you can use special micro-perforated waterproofing. It is needed specifically for this design, like a cold roof. Such material does not make it possible to lay different thermal insulation in the immediate vicinity; any further insulation will require spending money on the purchase of new material.
Important! If such conditions are not met, the roof will not be protected from moisture after some time. In this case, the insulation will always be wet, and the roofing material will be severely damaged by destructive corrosion.
For the installation process of a high-quality waterproofing membrane, it is necessary to remember that it can be installed with a certain sag of approximately 20 mm. This factor makes it possible to arrange the drainage of drops, which effectively protects rafters and other structural elements of the roof from excess moisture.
In order for water to be eliminated as efficiently as possible and not to stagnate, thereby creating a relatively unfavorable environment, it is imperative to provide a high-quality ventilation hole. It is carried out between the film and the roofing ridge.
Such a gap makes it possible to circulate under the roof without problems, and all traces of moisture and condensation will also be effectively removed.
Important! During the work, it is very important to ensure that the protective membrane does not have ruptures or any other defects, and it is fastened using a special construction stapler. It is mandatory to overlap, that is, all edges of the film must be secured using tape.
Of all the main features inherent in a cold roof, it is worth noting that it is possible to build it, if necessary, for any region of the country. Many people assume that this type of coating may not be suitable for some regions, but in reality this is far from the case.
For a standard living space, having a cold, unheated attic is a traditional solution in all respects.
It is worth noting that the use of a roof of this type will not affect the temperature of the upper floors. The attic space itself may not be used at all, and heat loss is solved by installing a layer of high-quality insulation between the upper floor and a special under-roof space.
In the process of constructing a cold roof, it is worth remembering such a stage of the work as proper insulation of all existing technological exits and openings. These are such structural elements as:
- Chimneys;
- Special mines;
- Entrances leading to the roof surface.
All of them require special thermal insulation. High-quality work will allow you to quickly avoid such unpleasant moments as the appearance of large amounts of condensation, icing, heat loss and the penetration of precipitation.
A device of such a design as a cold roof is one of the most common options due to its simplicity. The roofing pie contains the following layers:
- On the side of the rooms there is a layer of high-quality waterproofing, which has one-sided permeability;
- Roof truss system;
- Film from moisture, necessarily sagging a little;
- Counter-lattice, the construction of which is carried out strictly parallel to the previously installed rafters. Wooden boards of this system firmly press the waterproofing, that is, they provide another high-quality fastening;
- The sheathing of this cold roof design is made from high-quality timber made of wood. Its cross-section should be 50 by 50 mm. It is installed in a certain step, approximately 40 cm, but it is directly based on the category of metal tiles used;
- The topmost layer is the metal tile itself.
- A film is secured to the rafters using a special stapler or small galvanized nails, which provides waterproofing.
- Then it is pressed with fastening devices.
- The step directly depends on the category of metal tiles used.
- The size of such boards should be on average 25 by 95 mm.
- Sometimes professional builders use a continuous-structure coating made from sheets of high-quality plywood.
The film, which provides effective protective waterproofing, must be laid with sagging, but other defects are strictly unacceptable. The degree of sagging of the roof covering should be approximately 15-25 mm. This will provide an opportunity to guarantee the highest quality ventilation, as condensate will be removed.
The moisture will first go into the strip on the eaves, and then into the gutter. Neglecting this process will result in moisture completely destroying the roof.
When building a cold roof made of metal tiles, you must remember that a sheet of this material does not provide protection from noise. That’s why no one lives in the attic; it’s cool and noisy there.
To install a cold roof, you need to take relatively simple tools, as well as consumables that can be purchased relatively inexpensively. Special staples are used as the necessary fastening devices; these can be self-tapping screws or galvanized nails.
Important! In the process of calculating sheets of roofing material, you need to remember that you will definitely need additional elements such as valleys, ridge tiles, cornices, and so on.
The design of a standard cold roof differs from an insulated structure precisely in the absence of an insulation layer. Such a roof is erected if the attic will not be used as a living space.
The roof of a building is exposed to particularly intense influence of various natural factors, therefore, not only the comfort inside the house, but also the duration of operation of the entire structure depends on the reliability and quality of its design. Particular attention must be paid to the choice of material and the sequence of installation of roofing layers under metal tiles. The article provides information about the materials necessary for arranging a reliable roof - the main operational characteristics, the need for use, installation features, etc. After reading the article, you will be able to control the quality of the builders’ work, and if necessary, you will not allow them to “save” on purchasing cheap building and insulating materials or “simplifying” installation technology.
Source spb-artstroy.ruThe sequence and purpose of the layers of the roofing pie with thermal insulation
A roof pie made of metal tiles with insulation consists of several layers, each of which has its own purpose:
External covering. Metal tiles or its budget version - metal profiles (profiled sheets, corrugated sheets). It is recommended to use metal profiles to cover outbuildings and technical structures in roof structures without insulation;
Lathing. A wooden frame to which the outer covering is attached;
Waterproofing. Protects the rafter system and thermal insulation from moisture;
Counter-lattice. Wooden slats that create a ventilation gap between the outer covering and the insulating materials. Thanks to the counter-lattice, moist air and condensate do not come into contact with the thermal insulation;
Sound and vibration insulation. Damping elements are part of the roof frame of a large area. It is allowed to use such brands as Isoplast bi-not, Sylomer, etc. Roofing structures of small and medium sizes can do without them, provided that the load-bearing base (flooring) is carefully installed, fiber thermal insulation is used and the metal tile fastening technology is strictly followed;
Rafter system. The set of load-bearing elements of the roof, which is the basis for fastening all layers of the roofing pie;
Thermal insulation. Reduces heat loss from the building. It is recommended to use fibrous thermal insulation materials that have a high degree of sound insulation: mineral wool, basalt wool, glass wool;
Vapor barrier. Protects the roofing pie from moist air coming from the interior of the structure;
Internal counter-lattice. Wooden slats of small cross-section, creating a ventilation gap between the vapor barrier membrane and internal finishing materials;
Sheathing. Rough: plywood, OSB, plasterboard, intended for fastening decorative and finishing materials. Decorative: plastic or wooden lining, false beams, decorative panels.
Sequence of cold roof layers
The technology for arranging a cold roof is much simpler than an insulated one:
To the rafters using a construction stapler fastened waterproofing membrane;
Along the rafters strips are installed counter-lattice;
Lathing elements are fixed perpendicular to the rafters;
Fixed roofing material – metal tiles.
Cold roofing is used for technical structures, garages, warehouses and other outbuildings.
Main characteristics and features of the use of roofing elements
Rafter frame
For a metal roof, a standard rafter system for lightweight roofing materials is used. The section of the beam is 50x150 mm, the pitch of the rafter legs is 600-950 mm. As a rule, a pitch of 600 mm is adopted for ease of installation of thermal insulation materials. This distance allows you to place entire insulation slabs between the rafters without gaps and without the need to cut them, which will significantly speed up the installation process.
In the northern regions of Russia, it is recommended to use timber with a cross section of 50x200 mm for rafters. This is due to the need to withstand increased snow and wind loads, and also allows for thicker insulation to be placed between the frame elements.
Waterproofing
The choice of waterproofing material included in the roofing composition for metal tiles depends on the purpose of the structure. The use of ordinary polyethylene film, glassine or roofing felt is allowed for the insulation of non-insulated roofing structures used in unheated technical buildings.
Two-layer polymer– consists of two layers of polyethylene film with a reinforcing mesh between them;
Superdiffusion membrane– characterized by one-sided vapor permeability. Its location during installation is with the permeable side towards the insulation, so that moist air is removed from the thermal insulation into the ventilation gap.
Waterproofing with fleecy covering– is also a diffuse moisture-wicking material. In addition, it prevents the formation of condensation. Installed with the fleecy, vapor-permeable side facing the insulation.
Any of the waterproofing membranes is laid on the roof plane parallel to the ridge, starting from the bottom. The overlap between the panels is 10-15 cm and is additionally glued with construction tape. Fastening to the rafters is carried out with a construction stapler.
Counter-lattice
It is located between the sheathing elements and rafters, forming a gap between the waterproofing layer and the roofing material. It is made of wood in the form of bars 30x50 mm. If the roof has a complex structure, a large area or a significant length of the slope, then bars of a larger cross-section - 50x50 mm - are used for the counter-lattice. It is located along the rafters and attached to them with nails or self-tapping screws 50-75 mm long.
Lathing
It is a load-bearing base for metal tile sheets. It is made of boards with a section of 50x200 mm or timber 40x60 mm, located perpendicular to the rafters. In practice, these elements are often used together, if it is necessary to especially firmly fasten the outer sheets of metal tiles, in case of increased wind loads in the region and/or high windage of the roof structure. In this case, the main area of the roof is covered with timber, and the lower part of the slope is covered with a continuous plank flooring. The pitch of the sheathing elements depends on the wave of the metal tile and is 800-1000 mm. Fastening is carried out using nails or wood screws (self-tapping screws) 60-75 mm long.
Important! All wooden elements of the roof structure must be treated with antiseptic (against fungus, mold, rot) and fire retardant (increases flame resistance) impregnations. Manufacturers of construction chemicals also offer universal products for treating wood, which significantly increase the service life.
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Thermal insulation
The traditional thermal insulation material for roofing under metal tiles with insulation is mineral (basalt) wool. It is sold in rolls and slabs. The size of the slabs from most manufacturers is 1000x600x50 (100) mm. They are installed in the space between the rafters at random.
The use of slabs is preferable, since their installation does not require additional fasteners to hold the material between the rafters. Thermal insulation is laid as tightly as possible, but care must be taken to ensure that the material does not deform or shrink.
For insulation of technical buildings, it is more advisable to use polystyrene foam, since it better withstands moderate mechanical stress and does not require additional protection from inside the structure.
It is advisable to fill the gaps between polystyrene foam boards and between the insulation and rafters with polyurethane foam. This will not only eliminate the leakage of warm air from the room, but will also give the entire structure additional strength.
Vapor barrier
It is one of the most important layers of the roof pie under metal tiles. Its main purpose is to protect thermal insulation materials from the influence of warm, humid air coming from inside the premises. The use of vapor barrier is mandatory when using fibrous thermal insulation materials, since by absorbing moisture, mineral wool significantly reduces its effectiveness.
The most common vapor barrier material with an affordable price is glassine. However, it has low strength and durability. The polypropylene "woven" membrane is more durable and effective. It is produced under many brands and is positioned by the manufacturer as a universal insulating agent - hydro-wind-vapour barrier. In addition, this material prevents the formation of condensation.
Sound and vibration insulation
One of the specific properties of metal tiles is a high level of noise from external influences. Therefore, special attention is paid to sound insulation:
All design elements are fixed screws. The parts to be connected must be securely tightened together to prevent the formation of cracks and backlash;
Calculated position of sheathing elements in such a way that the edges of the sheet of roofing material are located on the supporting rail;
Installation of all elements of the lathing and counter-lattice is carried out without deviations from the working plane, as evenly as possible, without bumps or depressions. This will avoid distortions when installing metal tiles.
The noise level is significantly reduced by the use of fibrous thermal insulation materials. Some manufacturers produce specialized brands of thermal insulation with a high sound absorption coefficient, from 0.5 to 0.8.
It is advisable to carry out special measures for vibration isolation if the house is located near a railway, a highway with heavy traffic, or if the roof slopes have a large area. To do this, special damper pads are used to separate the layers of the roof under the metal tiles between the counter-lattice bars and the rafter beams.
Video description
In the video you can see the rules for installing a roofing pie:
Roof covering
High-quality metal tiles have a thickness of 0.4-0.6 mm and several layers of protection. It is almost impossible to visually check the presence of internal protective layers, so when purchasing roofing material, ask the seller for a certificate. To protect against corrosion, metal tiles are painted on the inside, and on the outside they have a polymer coating, which resists external influences much better than paints and varnishes. The durability and cost of the roof depend on the type of external protective layer. The most common types of polymer coatings are:
Polyester. The thickness of the protective layer is 25-30 microns. It has an affordable price and relatively high performance characteristics. The warranty period for metal tiles with polyester coating is 8-10 years;
Polyurethane. It is characterized by resistance to mechanical damage, temperature changes and various chemicals. When the sheet is bent, such a coating does not lose its integrity;
Polyvinyl chloride. Demonstrates high resistance to mechanical, chemical and thermal influences. Has high plasticity. Metal tiles with this coating are recommended for installation on textured surfaces. It is advisable to use in regions with extremely hot climates;
Plastisol. Consists of polyvinyl chloride with the addition of a plasticizer. It is applied in a layer of up to 200 microns, which allows you to apply a relief pattern to the surface of the metal tile. They have low resistance to high temperatures, which does not allow its use in regions with hot climates.
Interior decoration
A ventilation gap is also formed between the vapor barrier membrane and the sheets of plasterboard or OSB. For this, wooden slats with a cross section of 20x30 mm are used, attached to the rafters perpendicularly.
Video description
From the video you can learn how to properly make a roofing pie for metal tiles:
Conclusion
Despite the high cost of materials and significant labor costs when installing a roofing pie under a metal roof, it is highly not recommended to “simplify” the technology by skipping layers or using cheap insulating membranes from unknown manufacturers. The consequences can be very dire, including complete replacement of the roof.
The cold type attic is simpler than the insulated type, but there are subtleties here too. We analyze the arrangement of a roof with a cold attic, as well as advice from experienced builders.
The cold type of attics is most common in individual construction. It is rightly believed that building such a roof is easier than doing full insulation of the space under the roof. However, even when arranging a roof with a cold attic, there are non-obvious points. Let's figure out what mistakes inexperienced builders most often make and how to make a cold roof according to all the rules.
Thermal protection of a cold attic
According to physical laws, heated air rises and cold air sinks. In application, this means that heat from the house will tend to escape through the roof through any crack in the insulation. Therefore, it is necessary to create a reliable insulating layer in the path of the ascending warm flow. Its recommended thickness is 30-35 cm.
At the same time, the ascending air flow removes not only moisture, but also water vapor from living spaces. If you do not block the way for moisture, the wet insulation will cease to perform its functions and will turn into an ideal place for the development of bacteria and mold fungi. To block the path of water vapor, a layer of membrane material is laid under the insulation, permeable to gases, but retaining water.
Another problem when creating thermal insulation for a cold attic is the almost inevitable condensation of water on the underside of the roofing material in the evening. After sunset, the temperature outside drops quickly, so the roof cools down in just an hour. The air in the attic space remains warm much longer. In this case, dew will inevitably fall. To prevent falling drops from soaking the insulation, the roof is lined with a layer of waterproofing underneath.
The appearance of condensation on the insulation is unlikely. If the “pie” is constructed correctly, its bottom side will be warm and the top side will be cold. The air in the attic is renewed through the ventilation holes, and moisture does not accumulate in the insulation layer. Thus, the insulation of the floor provides reliable protection against heat loss, and the layers of waterproofing do not allow water vapor to accumulate in the attic.
Having understood the basic principles of thermal protection of the attic space, we will consider in detail all the components of a properly equipped cold roof in order to find out what pitfalls may be encountered during construction. To find out how best to insulate a ceiling under a cold roof, read this article.
Rafter system: how to correctly calculate the number of legs
The main task of the rafters is to become a reliable support for the roof. The rafter legs must confidently withstand the weight of the roofing material and the additional load created by wind and snow masses. While the weight of the roof is easy to calculate based on the properties of the selected material, the snow load is individual for each region. You can obtain data on average and peak loads from the regional meteorological service.
Since the roof will not be insulated, when calculating the distance between the elements of the rafter system, the width of the insulation layers is not taken into account. There are many frame options for cold roofs. The most common solutions fit into the following parameters:
- The lumber used is a board with a width of 10 to 20 cm and a thickness of 5-7 cm.
- The pitch between the rafter legs is from 0.6 to 1.2 m.
- The counter-lattice is made of boards 3-4 cm thick.
Online calculators will help you calculate each roof frame element that is optimal for the planned roof load. Such services (for example, kalk.pro) allow you to determine the geometric dimensions of each element, build a three-dimensional model and print drawings.
When creating a rafter system, it is extremely important to ensure that the outer surface of all rafter legs is positioned strictly in the same plane. If the rafters are not level enough, problems cannot be avoided when creating sheathing and roofing. In order to perfectly align all the elements, the outer rafters are rigidly secured with spacers, and a cord is pulled between them. To find out how to properly install a gable roof rafter system with your own hands, read.
Roof waterproofing: is it worth doing?
Insufficiently experienced builders often question the fundamental necessity of constructing a waterproofing layer on a cold roof. As an argument, an example is given of old-built village houses that have stood for decades without needing roof repairs, despite the lack of moisture-proof layers.
However, this argument does not apply to modern construction. The fact is that there are a whole range of significant differences in old and modern construction technologies:
- Old construction technologies involved the use of absorbent insulation. In different regions, mixtures of clay and sawdust, various industrial slags and other porous materials were used. A thick layer of backfill served as insulation and at the same time perfectly absorbed condensation. Modern insulation materials are hydrophobic, so water will flow into the ceiling, and this will not end well.
- In the old days, gables and roof overhangs were covered with boards without much effort, leaving many gaps. This roof structure was perfectly ventilated, so any leaks and condensation dried out quickly. Modern materials are much less permeable to air.
- Modern complex architectural forms of roofs make ventilation significantly more difficult compared to the simplest gable roofs.
- The roof of a village house was almost never finished from below. This made it easier to inspect and find damage. In addition, the attic was almost always used for storing various things. This means that any leak was detected (and corrected) very quickly. A modern house is built in such a way that there is no need to visit the attic, and it is much more difficult to detect a leak.
All these changes in construction technology have made roof waterproofing not an empty precaution, but an absolutely necessary element. Modern waterproofing films (for example, Yutafol D110, Yutakon, Izospan D) are cheap, easy to install and allow you to get rid of condensation forever.
Layers of insulating film are laid across the rafters. Each new layer is laid higher than the previous one. To prevent moisture from seeping between the strips, the installation is done with an overlap (the new sheet is layered on top of the previous strip by 6-8 cm).
After the entire roof slope is covered, the hydraulic barrier sheet is secured using a counter-lattice. It will reliably press the waterproofing film to the rafters and create an additional gap between the roofing covering and the waterproofing. The gap will facilitate the evaporation of condensate.
Installation of sheathing
Lathing across the rafters is done in two ways. Lathing made of solid sheets (OSB or moisture-resistant plywood can be used) is done if it is planned to use soft tiles or corrugated sheets for the roofing. Under the impact of raindrops, these materials make a lot of noise. Solid sheathing will reduce noise. In addition, it is easier to attach roofing decking to a continuous sheathing.
Lay the sheets from the front gable to the rear. Then all the additions will be located in that part of the roof that is least noticeable. With temperature changes, plywood (like OSB) will expand and contract, so leave a gap of 1-1.5 cm between the sheets. When installation is completed, the gaps are filled with roofing sealant to block the path of water.
In order not to doubt the reliability of the sheathing, use OSB with a thickness of at least 1.2 cm, and plywood - at least 0.8 cm. These parameters are optimal for a rafter pitch of 0.6 m. As the pitch increases, the thickness of the sheets of continuous sheathing is proportionally increased.
The second method of constructing sheathing involves the use of boards. In this case, both edged and unedged varieties are suitable, the main thing is that the thickness of the boards is the same. The boards are nailed to the rafters using regular nails. It is better not to use screws or self-tapping screws for this work.
Before installation, the boards are sorted by width. The widest lumber is placed along the slope so that it hits the joint between the sheets of roofing material. Narrower boards are allowed between the main elements. The pitch between the boards is selected based on the recommendations of the roofing material manufacturer.
Attic ventilation
There are two requirements for ventilation of the attic space:
- Sufficient vent area. So, if the roof area is less than 300 sq. m, an entrance door to the attic and one window on the opposite gable will suffice. If the roof area is large, additional vents are made in the upper part of the slope.
- Possibility of air flow control. In the summer heat, the ventilation holes are opened as wide as possible; in the winter frost, they are closed to prevent the attic from freezing out.
The total area of the ventilation openings is determined based on the area of the attic. 1 sq.m. vents will provide reliable ventilation of an attic of 500 sq.m. In this case, heat loss will not be any noticeable. The minimum acceptable ratio is 1 to 300.
To make it easier for you to imagine all the stages of work, watch the proposed video materials. They contain advice from experienced builders that will help you avoid mistakes in selecting materials and arranging a roof with a cold attic:
To ensure that the roof does not require repairs, and the house is warm in any weather, the construction of a cold roof must be approached as responsibly as possible. If each stage of construction is carried out in strict accordance with technology requirements, the roof will last for decades without requiring repairs.
Today, more and more developers are asking this question. The fact is that a cold roofing system allows you to erect a residential building for relatively little money, while an insulated roof requires enormous costs, both financially and in terms of effort and time. Having realized that such a system is in some sense better, many developers asked themselves the question: is a vapor barrier needed under a cold roof?
Cold roof design in a residential building
Many developers who want to save some money on construction strive to purchase the cheapest materials, but at the same time, so that the quality of the entire building does not suffer much from this. This is possible if you use primitive two slopes as a rafter system, corrugated sheets as a covering, and make the roof cold.
The design features of such a roof can be listed on one’s fingers, since there is no need to lay thermal insulation material, a vapor barrier layer and other components often found on insulated roofs. If you still doubt the savings, then we can say with confidence that the cold version will cost 50-60% less than the insulated structure. In addition, the work can be carried out independently, therefore, the savings will increase even more.
The cold roof pie, in most cases, includes the following products:
- Rafter legs
- Waterproofing material
- Counter-lattice
- Lathing
- Profiled metal sheet
Is waterproofing necessary for metal tiles on a cold roof?
It is worth noting that all metal surfaces have one similar feature: they collect condensation. The waterproofing included in the roofing pie with a cold roof will correct this problem and protect the room from incoming moisture both from the outside and from the inside. Many developers, when constructing an insulated roof, advise their friends not to lay a vapor barrier layer if they build a building with a cold type of roof. They think that the cold will remove the condensation that is visible on metal products, but they are very mistaken. 
Condensation appears due to the temperature difference between the roof space and the external environment. Naturally, when the attic is not heated and is not insulated in any way, the difference will be small, but still it is sufficient to provoke the release of moisture from the air. As you can see, condensation will form regardless of the type of roof, therefore, the question posed at the beginning of the paragraph can be answered unequivocally: yes, it is necessary.
An example is outbuildings whose owners do not care much about their service life. In such buildings, the roofing pie is the most primitive and even violates building codes. Most often, a roofing pie consists of rafters, sheathing and roofing. All layers of vapor barrier and waterproofing were simply thrown away. Despite this fact, this building can stand for a significantly long period, or, conversely, it can collapse in just a couple of years. It depends on your luck, but why take risks if you can do everything in a high-quality manner?
You cannot afford to take risks on residential buildings, as someone’s life may depend on it. I am not exaggerating, because if condensation affects the rafter system and other roofing elements for a long time, it will simply destroy them, which can lead to the fall of the entire roofing pie.
IMPORTANT: If at the beginning of construction you decide to build a cold roof, but later after a certain period you will insulate it, then it is most advisable to lay micro-perforated film as a waterproofing product. Its properties are practically no different, but the price tag is much lower than membranes.
Waterproofing and ventilation of cold roofs
If you are laying a micro-perforated product, then such a layer will block the access of moisture from the outside, but at the same time water vapor can pass through this area without problems. We can say that laying vapor barrier products on roof slopes is not necessary in this case. After steam penetrates inside, it ends up between the waterproofing material and the metal coating, from where it is removed by natural ventilation. 
IMPORTANT: When a dense waterproofing film that retains water vapor is used, this leads to a significant increase in air humidity and, as a rule, dampness in the room.
With increased air humidity, condensation processes begin, so moisture accumulates on the back side of the film and penetrates all roofing materials. Due to this fact, for the construction of a cold roof it is not recommended to use materials such as polyethylene and polypropylene, roofing felt, and glassine.
The ventilation system for cold roofs is quite simple. To create it, gaps are left, which, as a rule, are located along the eaves overhang. Air masses pass through them, collect all the humidified air and remove it through the cold triangle located in the ridge part of the roof.
The counter grille is a design to provide additional ventilation. Most often it can be found on complex roofing systems, where products with a high degree of waterproofing are used as a coating, for example, metal, bitumen shingles and others. The gap that is created by installing counter-battens allows fresh air to dry the roofing pie on both sides, so structures with such a pie last much longer than others.
Cold roof. Is waterproofing necessary on outbuildings?
First of all, it is worth noting that outbuildings differ significantly from residential buildings both in their structure and volume. The vast majority of developers are trying to save money on the construction of secondary structures, so the issue of waterproofing is more relevant than ever. Before answering the question, let's look at the coating. Today, corrugated sheeting is one of the cheapest materials, so I will talk about buildings covered with it.
Manufacturers from different countries are striving to produce such products so that the whole world can use them. If you are a fan of corrugated sheets, then today such material is a sheet of metal with an anti-condensation coating. 
In appearance, it is practically no different from its analogues. A synthetic composition is applied on the inside; it resembles felt. Due to the large number of pores, this material is capable of retaining up to 1 liter of water per square meter. After the surface has been saturated with moisture, ventilation comes into play and if it is carried out according to all the rules and regulations, the drying process will not take much time.
Thanks to the installation of such a “tricky” coating, the need to lay a vapor barrier and waterproofing layer is eliminated, but it should be understood that the weight of such a coating will vary depending on weather conditions. When making the necessary calculations, it is very important to take these parameters into account and use them in the calculations. It is worth noting that a finished roof will be much cheaper, because it will not contain almost half the roofing pie.
Installation of waterproofing for cold roofs
So, based on the information obtained above, you understand that waterproofing material is installed regardless of the type of roof and the functional purpose of the building. However, if you want to save money, you can use roofing coverings with an anti-condensation layer, but not all people like metal coverings, so I will now tell you the general principle of installing waterproofing.
- First of all, an inexperienced roofer must repeat safety precautions and the principle of working at height. After this, he dresses in special uniform, which should include the following: personal protective equipment, good shoes with non-slip soles and a mounting belt.
- After the rafter legs have been secured in place, you can begin laying the vapor barrier layer. It is attached to the rafters using a construction stapler and pressed against the sheathing. With a small slope, strips of material are placed across the slope, and along highly inclined slopes. To improve the quality of laying this layer, the joints are coated with bitumen or taped with double tape.
IMPORTANT: Before installing the sheathing, it is very important to treat its elements with special protective solutions, which will increase the degree of ignition of the wood and protect it from rotting.
- Next, the counter-lattice is laid. It creates the necessary air gap, thanks to which moisture will be removed from the roofing pie.
- Waterproofing material is laid on top of the conro-lattice.
- After this, they begin to install the corrugated sheets.
Most developers strive to cover as much length as possible with one strip of corrugated sheet. This is justified by the fact that in this way fewer joints are obtained, therefore, the waterproofing qualities of the entire roof are significantly increased. You can do all the work yourself, but to increase efficiency it is better to invite 1-2 partners.