Every year, residential buildings, like any other buildings, are subject to increasingly stringent requirements for energy efficiency and comfort. But there are no materials that by themselves could provide a solution to the entire range of tasks. That is why modern construction technologies almost always involve the creation of complex enclosing structures with a large number of layers - instead of arrays of one material, even the most practical one.
A pitched roof is no exception; on the contrary, it is often even more intricate in its structure than the outer walls. It’s not for nothing that a roof is called a system, because it consists of many interconnected elements, each of which plays its own role, each of which is important. The word “pie”, regarding the roofing structure, is also not used by chance, since multi-layering here has become an generally accepted norm that cannot be challenged. We propose to consider what a multi-layer roofing system consists of and how it all works.
What a modern roof should be able to do
If we want to learn how to consciously choose materials and carry out installation without doubt about the correctness of our actions, then it is better to understand the processes that occur inside the building envelope during operation.
The roof protects the house from precipitation; under no circumstances should it leak - this is an axiom. It is a barrier to dust, leaves, birds, insects... It prevents street noise from entering the rooms.
But also in many private cottages, attics are used as living quarters. Then, to protect the house from heat loss, insulating materials are placed not in the attic floor, but in the roof between the rafters, because now there is only the roof between the heated room and the street.
In this version of organizing space, the system begins to be affected not only by external forces (wind, rain, ultraviolet radiation, high and low temperatures, birds...), but also by harmful factors from within. First of all, these include water vapor that moves from indoors towards the street.
Water evaporation is generated by people in the process of life. In winter, when the temperature in the rooms is much higher than the outside, a pressure difference occurs, and vapors with a fairly high pressure penetrate through diffusion into all surrounding structures. If an impenetrable barrier gets in their way, and the ventilation system cannot cope, then we are faced with the problem of condensation (as, for example, on double-glazed windows and metal-plastic window frames). Condensation is harmful to most materials. In a roofing system, the following may be affected:
- Insulation. Water is absorbed into mineral wool, and therefore displaces air, and the heat transfer resistance of mats and slabs is sharply reduced. Mineral wool not only holds water inside, but can also pass it through itself, that is, it is possible to organize the weathering of “excess moisture”.
- Bearing structures. They can gradually collapse due to corrosion (trusses made of rolled metal, reinforced concrete) or rotting and other types of biological contamination if boards or timber are used to create rafters and sheathing.
- Roofing coverings. Metal sheets (rebates, corrugated sheets, metal tiles) corrode when drops of condensation fall on the inner surface; other materials, when regularly moistened, freeze, rot, mold, etc.
However, even knowing the enemy by sight, it is difficult to fight him. It is almost impossible to reduce the flow of water into indoor air. We all breathe, cook, wash, wash - this is all comfort to which we have long been accustomed. Even with the help of powerful forced ventilation It will not be possible to completely remove moisture outside the house. There is only one thing left - to learn how to manage water in order to prevent steam from harming our home. Where necessary, we put up an impenetrable barrier for moisture; where we need it, we allow it to escape freely through weathering and evaporation, we organize ventilation gaps, vent openings...
If we want to make the roof effective and durable, we need to use all the layers provided by the technology. It is equally important to observe the order of the relative position of the layers, the dimensions of the calculated gaps and distances.
Basic structure
In some sources on the Internet, only the “filling” of the structure (insulation + insulating films) and finishing coat. We believe that it would be correct to consider the system exclusively as a whole, because everything here is inextricably interconnected.
The construction of the roof begins with the installation of mauerlats and the installation of rafters. In this case, the timber or board from which the rafter legs are made are selected according to the cross-section in such a way that the roof can withstand any emerging loads. To solve this issue, you will need a project; you will find out why you need it in the article of the same name. In addition, for the manufacture of rafters, lumber is taken so that insulation of the required thickness can be laid between them. For example, in some cases, when large heat losses are planned and it is necessary to make an insulated roof, it is worth choosing a 50x200 board over a product with a section of 50x150 mm. You will find more information on this topic in our article on rafter structures.
Insulation of roof slopes
According to thermal imaging inspection data of a poorly insulated building in use, one can draw clear conclusions that the lion's share of thermal energy losses occurs through the roof. Therefore, effective thermal insulation in this area is of utmost importance.
Depending on whether the house has a residential attic or is equipped with a cold attic, the insulation method is selected:
- On the attic floor.
- Inside the roof slope.
An insulated roof has a more complex structure, which, in addition to the heat insulator, also includes: vapor barrier, vapor-permeable waterproofing, ventilation gaps... Cold roof does not require the use of vapor barrier films, but waterproofing sheets are used, and ventilation gaps usually exist.
The following materials can be used for insulation:
- Styrofoam,
- extruded polystyrene foam,
- mineral wool.
Due to a number of reasons (vapor permeability, flexibility, elasticity/resilience, non-flammability, low thermal conductivity...) watt insulation is used most often in roofing structures. Manufacturers offer for pitched roofs special lines of basalt or fiberglass wool - called “Roofing”, “Roof”, etc.
As a rule, these are relatively lightweight materials that are intended for installation inside non-load-bearing structures. A density of 35 kg/m3 is enough for the slabs or mats from the roll to expand tightly and without gaps (cold bridges) between the rafters and not slide under their weight in the inclined cavities of the roof slope.
As for the optimal thickness, to insulate a roof with a residential attic below, the insulation is selected depending on the calculated heat balance of the building and the climatic conditions where the house will be used. For example, this table is given to us by the Rockwool company (one of the most reputable mineral wool manufacturers) for its popular Light Butts cotton wool:
Dependence of insulation thickness on region
Some companies produce insulation of such a large thickness, but it always makes sense to combine several thinner layers, laying out the materials with overlapping joints, which avoids blowing through possible gaps. That is, it is better to obtain an estimated insulation thickness of 150 mm by using slabs 100 mm thick, and add it in one 50 mm layer, and, say, 200 mm of wool is better collected by the sum of two layers of 100 mm or according to the formula 150+50 mm.
Vapor barrier
We have already talked about possible harm, which can be caused by water vapor moving from rooms towards the street. If nothing is done, all layers of the roofing pie suffer from condensation, from insulation and roofing to power structures made of metal or boards and timber. That is why houses with residential attics and insulated roofs are always equipped with vapor barrier protection.
Roof vapor barrier is a film impermeable to water vapor. This can be a special branded material with several working layers of polyethylene and polypropylene (sometimes with reinforcement, a reflective metallized coating), or ordinary transparent polyethylene, including reinforced polyethylene - with increased UV stability and resistance to tensile loads.
Vapor barrier sheets are secured using double-sided adhesive tapes, staplers, and pressure strips. The joints and junctions of the strips must be taped with tape. Some manufacturers of multilayer vapor barrier materials recommend leaving a gap of about 1 cm between the film and the inner lining of the attic. Since the working properties (vapor permeability, water column height...) of modern vapor barrier materials are often not the same from different sides, it is necessary to maintain the correct orientation of the panels during installation. Usually the printed logo of the canvas is turned inside the room; if there is foil on the vapor barrier, then use it.
Waterproofing
Nowadays, high-tech membranes are used in the system of insulated pitched roofs. They, depending on the design features and the type of roofing used, can perform several functions, the main of which is additional protection of the under-roof space from the ingress of water from the outside (slanting rain, melting snow, blown by the wind). They also prevent blowing of the insulation and weathering of fibers from mineral wool slabs/mats.
Many roofing membranes are vapor permeable, which allows moisture trapped in the insulation to evaporate, leaving the thermal insulation dry, and therefore operational. Here we also have a multi-layer synthetic fabric, only with micro-perforation. This membrane combines the ability to retain dripping water from the outside and the ability to pass steam from the inside. Depending on how clearly these indicators are expressed, the following can be distinguished:
- Superdiffusion, diffusion membranes.
- Pseudo-diffusion membranes, vapor-tight water barrier.
Diffusion and superdiffusion membranes have very high vapor permeability values; they allow you to create a so-called “breathable” roof. However, the final roofing coating must ensure the weathering of passing moisture and not be afraid of condensation and corrosion. For example, such membranes cannot be used with metal tiles, corrugated sheets, or seam roofing, since due to their high thermal conductivity from below, the sheets can become covered with condensation and be destroyed. If you nevertheless decide to combine a vapor-permeable membrane and a metal-based roofing covering, then the ventilation gap should be a mandatory element of the roofing pie. In other cases (natural tiles, various slate options, straw, bitumen shingles, wooden shingles, etc.) they have proven themselves very well, and, as a rule, there is no need to make ventilation gaps between the insulation and the waterproofing sheet.
Perforated films with a low (or close to zero) coefficient of vapor permeability require the creation of an additional gap on the insulation side, since they are not able to pass all the moisture through themselves and condensation may fall out from the bottom side, which then accumulates into the insulation. An additional measure for regulating water drainage can be considered the requirement to create a slight sag of pseudo-diffusion and impermeable sheets between the rafters, but without touching the insulation.
A separate type of such films can be considered “anti-condensation” models, which go well with metal tiles, corrugated sheets, and seam roofs. Their trick is the presence of a fleecy layer at the bottom. Under conditions favorable for condensation, it is saturated with moisture, retains drops and prevents them from falling down into the mineral wool. With daily change temperature regime and atmospheric humidity, at a certain moment the moisture from such a hydrobarrier begins to erode. That is, the work of the anti-condensation fabric is based on adsorption, not diffusion.
Install waterproofing films and membranes across the slope - horizontally. At the ridges of hip structures and in valleys, additional strips are pre-laid along these vulnerable nodes. It is imperative that the waterproofing extends to the very end of the overhang so that water can enter the gutters. It is also necessary to overlap adjacent panels - at least 15 centimeters. Any of the waterproofing films in the insulated roof system must be supplemented on top with a ventilation gap of 5 cm or more.
When choosing a membrane or hydrobarrier, you should pay attention to the following properties of the material:
- Water resistance,
- Vapor permeability level.
- Resistance to UV rays (determines how long the material can be exposed before installing the roofing).
- Tensile strength.
Buy from trusted manufacturers and suppliers. The service life of the insulation and the entire roofing pie as a whole depends on the membrane.
Roof ventilation
Removing moisture from an insulated roof structure is a prerequisite for the efficiency and durability of the entire system. This can only be ensured if ventilation gaps are properly organized. The air in the under-roof space is heated by the sun and, through convection, begins to move from bottom to top, carrying excess moisture outside.
In roofs with a large slope, this process occurs more intensely than in slopes with a small angle. Therefore, natural ventilation is usually sufficient here. But for systems of complex shape, long slopes or too flat ones, you need forced circulation, which is provided using electric fans. Natural ventilation of the roof is carried out through a set of measures. The selection and installation of each element must be taken extremely responsibly.
1. Creation of ventilation gaps. There may be several of them. For example, when using a vapor-impermeable water barrier, a double gap is needed: between the insulation and the waterproofing sheet, between the waterproofing and the roofing.
The size of the gaps is calculated for each roof individually, as it depends on the length and area of the slope, its angle of inclination, and the type of materials used. But we can definitely say that the upper gap should not be less than 50 mm. To create ventilation gaps, counter batten bars of the appropriate cross-section are used, which are screwed along the rafters.
The dependence of the height of the ventilation gap on the roof parameters can be traced using the numbers in the table:
Dependence of ventilation gap height
| Roof slope length | Tilt angle 100 | Tilt angle 150 | Tilt angle 200 | Tilt angle 250 | Tilt angle 300 |
|---|---|---|---|---|---|
| 5 meters | 50 mm | 50 mm | 50 mm | 50 mm | 50 mm |
| 10 meters | 80 mm | 60 mm | 50 mm | 50 mm | 50 mm |
| 15 meters | 100 mm | 80 mm | 60 mm | 50 mm | 50 mm |
| 20 meters | 100 mm | 100 mm | 80 mm | 60 mm | 50 mm |
| 25 meters | 100 mm | 100 mm | 100 mm | 80 mm | 60 mm |
2. Creation of vents in the roof overhang structure, for access of street air inside the roof. In the lower part of the hem, materials with perforations are used (the so-called roofing “soffits”), and vent openings are made with gratings and meshes that prevent birds and insects from entering the roof. If profiled material is used on the roof (slate, corrugated sheets, natural tiles), then the area of inlet openings/openings can be reduced, for example, by using soffits with partial perforation, and if the finishing coating is flat material(carpet of bitumen shingles, seam paintings), then you need to use as much as possible large area vents to ensure air flow.
3. Elimination of any obstacles to the circulation of air. No additional bars, no sheets or parts of thermal insulation should block the ventilation gap along the line “from the eaves to the ridge”. To combine the “chambers” that are formed after installing the counter-lattice bars, and to ensure the mixing/flow of air throughout the slope (stagnant zones are eliminated, the temperature is evenly distributed), it is recommended to install the lumber used to create the counter-lattice with gaps.
4. Creation of openings in the ridge area to allow air to escape along with excess moisture. For this, special ridge elements with outlet holes are used, as well as “aerators”, which are installed in the upper part of the slope (about 50-70 centimeters from the ridge). The number and size of aerators is selected individually. For example, one aerator with an outlet area of 130 square centimeters is enough to provide ventilation for 25 square meters of a slope covered with bitumen shingles. In order to protect the under-roof space from birds and insects, gratings and nets are also used here. Some roof aerator models use a barrier made of dry granular litter.
Conclusion
You can't skimp on your roof! Everything is important - the correct calculation of the supporting structure, competent and sufficient insulation, the quality of all materials, and installation by high-level specialists. Only then will the roofing pie work as a single unit for a long time and flawlessly for decades. A major oversight in any of the above components can lead to costly alterations and repairs. In addition, the roof determines the unique and inimitable design of the entire house.
Often during construction, owners of private houses try to use even the attic area for living quarters. Some of them plan only summer-type rooms (unheated) on the attic floor, but preference is still given to full-fledged rooms in which you can live all year round. And this circumstance directly affects the arrangement of the roof. If in attic rooms the insulation is usually laid on the floor to insulate the heat coming out of the lower floor, and the empty space of the attic itself serves as an air layer that prevents cold from penetrating from the roof into the rooms, then the attic room is insulated differently. All insulation from the floor must be transferred to the roof structure. Therefore, in attic-type houses, a mandatory element of the roof is a roofing cake - a multi-layer system of different materials that provide heat, hydro, vapor barrier and ventilation.
In a roofing pie, each layer performs a specific function, but subject to the correct order of placement. It is better to entrust the creation of such a pie to professionals, but every owner should be aware of what it is in order to control the quality of the installation, check whether all the layers are laid in the correct order, and know what materials are best to purchase. If the installation of the roofing pie does not comply with the standard, then heat loss will occur through the roof, condensation will form, and in winter - ice and icicles. This means that all the insulation was done in vain.
Each layer has its own purpose and is inextricably linked with the others. An error in the installation of one of them leads to a reduction in the service life and performance characteristics of the roof.
Let's consider the sequence of laying layers, and what materials are best selected for each layer.
Uninsulated roofing pie
It is created in cases where people plan to live on the attic floor only in the summer, and the ceiling of the main rooms is already insulated. In this case, the main task of the roofing pie is to isolate the attic from condensation entering from the outside, and to allow moisture to escape from the house to the outside. To prevent air microcirculation from being disrupted, a waterproofing film with tiny holes (micro-perforation) is laid.
The sequence of laying an uninsulated cake is as follows:
- A rafter system is created.
- A waterproofing film is laid.
- The counter-lattice is being filled.
- The sheathing is attached.
- Roofing material is laid.
Read on to learn more about the installation features of each layer.
Insulated roofing pie
This is a more multi-layered structure, which is used for attics in which it is planned to equip full-fledged residential premises. And its task is not only waterproofing, but also heat preservation. The thermal regime under the roof differs significantly from the climate on the ground floor.
An insulated roofing pie can turn an attic into a living space
In summer, the roof can heat up to 70˚, and in winter it can get very cold. Of course, there can be no comfortable living in such a room. Therefore, the roofing pie must not only retain heat inside during the winter, providing air insulation from contact with the cold roof, but also prevent hot air from coming into the house during hot weather.
The attic loses heat more intensely than the lower floors, since it has a larger total surface of contact with the external environment
Let's look at the structure of an insulated roofing pie in more detail.
Rafters
The total thickness of all layers of the roofing pie is about 35 cm, so the rafter system must take this into account. To know for sure whether the height of the cut rafters is enough, decide what material you will use as insulation. For example, basalt insulation has a thickness of about 150 mm, so timber with a traditional thickness of 100 mm will be too small.
The rafters, which will bear the main load of the roof, are best made from coniferous wood, which has no flaws. Choose wood with a moisture level of no more than 22% and be sure to saturate the entire wood antiseptic compounds.
The rafter structure must be treated with antiseptics before laying the roofing pie
The thickness of the rafters and their pitch are selected depending on the covering that will be used to cover the roof.
Vapor barrier layer
It is from this layer that the installation of the roofing pie begins, although the last inner layer will be the finishing.
Why do you need a vapor barrier layer?
There is always moisture inside any house, and there is more of it in the warm air, which, according to the law of physics, tends upward, i.e., into the attic floor. Neither natural nor forced ventilation can completely remove excess moisture, and when it gets on the roof structure, it settles as condensation. In our case, the vapor barrier layer must protect the insulation, which is laid as the next layer, from moisture penetration, since the thermal insulation material saturated with moisture completely loses its properties.
What material is used for the vapor barrier layer
- Glassine is an affordable vapor barrier, but its ability to retain moisture is lost over the years.
- Vapor barrier film. As a rule, such a film has several layers and a reinforcing frame made of polymers, which prevents it from sagging.
- Foil material.
Foil as part of a vapor barrier material will increase the level of heat retention, since it does not transmit infrared radiation
This can be a film with a foil side or a material reminiscent of chocolate wrapper, in which one side is paper and the other is made of foil.
Both options, in addition to waterproofing, perform another important function: they do not allow infrared radiation to pass inside. And since it is precisely this that causes heat loss from the premises, then with the use of a foil layer, heat loss is reduced (and this is without insulation!). In terms of price, this waterproofing material is more expensive than others.
How to attach a vapor barrier layer to the rafter system
- The material is rolled out along the rafter legs. As a rule, waterproofing film is sold in rolls, which must be rolled out along the ridge. Laying begins from the bottom, and the rows are laid overlapping, extending 15 cm onto the previous layer.
- The most convenient way to fix the film to the wood is with a construction stapler.
- The places where the rows are laid and the edge adjacent to the wall must be sealed, secured with connecting tape. Instead of tape, you can carefully glue it with tape.
note! There is no need to stretch the film too much. It should sag slightly between the rafters (up to 2 mm).
All rows of vapor barrier film begin to be laid from below, and the joints are tightly sealed with tape
Thermal insulation layer
If you plan full-fledged rooms on the attic floor, then the microclimate and heat level in them should be no worse than in the rooms on the main floor, which means they need to be insulated with the same quality. Moreover, the ceiling (aka pitched roof) has a large surface area in direct contact with the street, which leads to significant heat loss. The thermal insulation layer of the roofing cake will help reduce them.
How to choose the right insulation
There are many materials for insulation on sale. But for a residential building, the thermal insulation material must meet the following requirements:
- be environmentally friendly;
- non-flammable;
- vapor permeable;
- isolate sound.
Let's consider which insulation materials are used most often.
Mineral wool. The most commonly used insulation. The material is based on basalt fiber, does not burn, has a dense structure, high level heat preservation. But you shouldn’t buy it for a roofing cake under metal tiles, because the condensation formed on the back side of the roofing can penetrate into the mineral wool and quickly saturate it, causing the insulation to lose its properties.
The soft structure of mineral wool completely fills the volume even in the most inconvenient areas of the rafter structure
Fiberglass. Non-flammable, environmentally friendly safe material. But the structure of fiberglass is unstable and tends to “slip”. Therefore, it is not recommended to cover pitched roofs with such insulation, but only flat ones.
Both mineral wool and fiberglass should be laid on roofs with difficult areas. They easily fit into any niches, filling the entire volume between the rafters completely, thereby preventing cold bridges.
Styrofoam . Popular due to its low price and good thermal insulation. A big plus is that it does not absorb moisture. But it should be borne in mind that it is flammable, and when burned it forms toxic compounds.
Expanded polystyrene. Demanded due to its lightness and low thermal conductivity. Non-toxic and does not absorb moisture at all. But due to vapor permeability, increased humidity may be observed in the room in summer. But in case of roof leaks, moisture will not get inside from the street. Expanded polystyrene boards have a rigid structure, so they are difficult to lay on difficult areas of the roof.
So, to summarize: for pitched roofs it is best to use insulation with a loose structure, and hard materials are suitable for a soft roof.
What layer of insulation is placed in the roofing pie?
The minimum layer of insulation for areas with mild winters should be at least 15 cm. If winters are frosty, then it is better to lay 20 cm thick.
If one layer of insulation is not enough, apply a second one on top
The ventilation gap serves as an air gap between the insulation and the waterproofing film, which will prevent moisture from entering from the outside. It is needed to ensure that excess moisture is removed from the insulation, which is formed in the off-season, when there is high humidity outside, or that gets through cracks in the roof, etc. In roofs with a roofing pie, it is very difficult to find and eliminate leaks, because entire blocks of mineral wool may get wet in one place, and a crack will appear somewhere near the ridge. And if you do not provide an air gap, then during the season, with such a leak, a large amount of insulation can deteriorate (especially fiberglass and mineral wool, which absorb moisture).
How to create a ventilation gap:
- If a corrugated material is chosen as a roof covering, then passive ventilation will be created in any case, even if the ridge structure is flat.
- For forced ventilation, you need to purchase special equipment that is driven by the wind or powered by electricity. This includes aerators and special ventilated skates.
- On pitched roofs, natural ventilation is sufficient, but on flat roofs, forced ventilation is required.
With roof ventilation, moist air is easily removed from under the roof, either by natural draft or using special ventilation valves
Waterproofing layer
The task of waterproofing is to prevent moisture from the roofing from entering the thermal insulation layer, but to remove excess moisture from the insulation. Therefore, the film that was laid in the vapor barrier layer will not fit here: it does not allow moisture to pass through. For waterproofing, special materials are purchased, including:
- Diffusion membranes
This is a film coating in which there are microscopic holes, shaped like funnels. The wide side of the funnels is laid against the insulation, and the narrow side against the roof covering.
They can only be laid if 2 ventilation gaps have been created. Contact with the insulation is not allowed, because the funnels will become clogged and will not allow steam to pass through.
The moisture in such pies escapes under the roofing material, so diffusion membranes are allowed to be used with roofing coverings that are not afraid of condensation on the back side.
These films introduce vapor so effectively that they do not require the creation of an air gap. This is convenient for those houses where the roofing pie is not created immediately during the construction process, but in an already residential building.
Superdiffusion membranes are the most popular materials for protecting the roof of a house from condensation, leaks and external moisture.
Both membrane options are not suitable for metal tiles and euro slate, because the back side of these coatings is afraid of condensation, but roofing tiles under soft tiles and clay tiles are installed with this type of waterproofing.
- Condensation films
They are used on roofs made of metal tiles and euro-slate, because the films are vapor-tight. Moisture from the insulation settles on the fleecy surface of the waterproofing layer and is carried out with ventilation. The second air gap (under the roofing) prevents condensation from settling on the back side of the roof.
Counter-lattice and sheathing
After laying the waterproofing, the counter batten bars are filled, and the main sheathing is laid over it. The type of sheathing depends on the roofing material. For soft tiles, ondulin, a continuous sheathing is made of oriented strand board, plywood or boards; for slate, metal profiles, etc., the sheathing is made of bars with gaps for ventilation.
The sheathing for metal tiles is made from bars to create an additional air gap that will prevent condensation from settling on the back side of the covering
The roofing covering is laid on top of the sheathing.
Video recipe for “layer cake” under metal tiles
Now that you know all the nuances of the roofing pie, you can safely invite the construction team and observe from the side that the work is being carried out correctly.
Experienced craftsmen rightfully call metal tiles one of the most practical, affordable and reliable roofing materials. It is suitable for use even in difficult climatic conditions, as it is highly weather resistant. However, in order for this functional coating to reveal its full potential, it is necessary to properly arrange the roofing pie for it, using compatible insulating materials. In this article we will talk in detail about the construction of a metal roof.
Metal tiles are profiled roofing sheets made of galvanized steel with a polymer coating, the relief of which resembles a wave. This material is recommended for use if the roof slope is 15-45 degrees. Roofing pie for this coating is composed in such a way as to minimize its disadvantages - high thermal conductivity and resonating ability. Therefore it consists of the following elements:
- Vapor barrier. This roofing layer is intended to protect the thermal insulation material from exposure to air saturated with water vapor and condensation. It is made from durable polymer materials.
- Thermal insulation. Insulation is placed between the rafters to maintain the temperature of the under-roof space. Mineral or polymer materials are used as insulation under metal tiles.
- Waterproofing. Waterproofing – required element roofs made of metal profiles, which serve to protect rafter frame and insulation against atmospheric moisture and condensation.
- Counter-lattice. It consists of slats made of coniferous wood 3-4 cm thick. The counter-lattice is fixed along the rafters on top of the waterproofing to provide a ventilation gap.
- Lathing. Metal tiles are laid on a sparse sheathing made of wooden blocks or edged boards, the pitch of which is 50-100 cm, which ensures the lightness and strength of the roof.
Note! The finishing coating, a metal profile, is laid overlapping, so the roofs are sealed and well protected from leaks. The lower the roof slope, the more overlap is made during installation. The roofing pie for metal tiles ensures the durability of the finishing coating and the rafter frame.
Types of roofing pie
Depending on the shape and purpose of the roof, the roofing pie for metal tile flooring may vary. Its composition and layer thickness are significantly influenced by climatic conditions in the region where construction is taking place. There are 2 main types of metal roofing:
- Cold. They are called cold ones, which are mounted above an unheated attic. They do not provide thermal insulation, so they are cheaper. Inexpensive materials, in particular roofing felt, are used as waterproofing for them. Easier to install, cold roofs are used for the construction of seasonally used or garden houses.
- Warm. A warm roof is installed if a residential, heated attic is installed in the under-roof room. To avoid heat loss through a large area of the roof slope in contact with atmospheric air, a layer of insulation, vapor barrier and vapor-permeable waterproofing are included in the roofing pie.
Important! Roofs of any type made of metal tiles can last more than 25 years, provided they are installed correctly, timely maintenance and proper operation. The composition of the roofing pie, the required sequence of layers and the selection of compatible materials prolongs the operation of the finishing coating, preventing corrosion and rotting of the rafter frame.
Thermal insulation requirements
The high resonating ability of metal tiles is a feature of the material that must be taken into account when composing a roofing cake. To reduce noise during gusts of wind, rain or hail, roof insulation with such a coating must also perform a sound insulating function. Therefore, the following requirements are imposed on it:
- The insulation must have a high noise absorption coefficient, at least 0.5. Therefore, foam plastic is not used for thermal insulation of metal tiles. Basalt fiber, glass wool, and mineral wool have good sound-absorbing properties.
- The thermal insulation material must have a low dynamic modulus of elasticity. This indicator reflects the relationship between the density of the insulation and the speed of propagation of sound waves in it.
- It is important to choose elastic insulation that retains its shape well and does not wrinkle.
- Low hygroscopicity. Insulation with low hygroscopicity will not lose its thermal insulation properties when wet, which will serve well in case of leaks into the rafter frame.
Please note that most thermal insulation materials lose effectiveness when wet. The thermal insulation properties of insulation with increasing humidity are reduced by more than half, so reliable membrane waterproofing and vapor barrier are included in the roofing pie for metal tiles.
Video instruction
Every year, manufacturers of bituminous materials produce more and more new coatings, but at the same time the roofing pie is under soft roof remains unchanged. The exception is its minor changes based on the finishing layer used. Today, soft roofs have high waterproofing and elasticity parameters, therefore, working with them is not difficult. In this article I will describe what the pie should consist of so that the roof does not require expensive repairs in the first year of operation.
Indicators of soft roofing
The construction of a roof made of soft products is carried out in several layers. Not only the effectiveness of the protective layer, but also the service life of the entire building depends on their location. For example, without installing a vapor barrier layer, the thermal insulation slabs will quickly become saturated with moisture, and you will have to replace them, and without eliminating the cause, this will happen again.
Today, bituminous shingles almost entirely occupy the niche of soft roofs. In fact, this type of roofing is recognized precisely by this product. The raw material for the production of soft tiles is most often fiberglass impregnated with a special bitumen compound or rubber. The protective layer, as a rule, is a mineral coating.
In addition to tiles, a material called shingles is common in private construction. Its advantages are as follows:
- Increased resistance to aggressive external environments. Bituminous materials have the highest possible moisture resistance and can withstand temperatures from -50 to +100 degrees. They never become covered with moss and do not rot, therefore, they are not attractive to other small rodents
- The operating period is about 25 years, which is quite impressive considering the cost of this material. This indicator may be higher if during the installation work the processes proceeded with maximum quality
- The soft surface is good sound insulation. Its noise-absorbing properties are the highest priority for some developers along with all the positive aspects
- Simplicity of installation work. As mentioned above, bitumen products are highly elastic. This allows you to easily lay the material even on difficult rafter systems. Thanks to the properties of the coating, installation work can be carried out independently. For this you will need a good gas-burner and special uniforms for working at heights
The use of soft roofs is only advisable if the slope of your roof is in the range of 15-45 degrees. Laying roofing carpet from individual elements on flatter planes is fraught with leaks. The fact is that the fastening method does not make the surface completely sealed. If your region has high temperatures during the hot season, then it is better to make the slope as small as possible, this is due to the fact that with strong heating, the bitumen product can drain from a steep slope.
The introduction of new technologies into production allowed manufacturers to create the new kind soft tiles. It is practically no different from its analogues, but has a self-adhesive base. Thanks to this, installation work can be carried out in a very short period and you do not need to use many tools.
To get acquainted with the product, I advise you to study its structure, which includes the following layers:
- There is a protective film on the bottom of the bitumen product. It performs the protective functions of a self-adhesive layer
- The composition of the adhesive allows for high-quality gluing of the bitumen material, both to the sheathing and to another identical element. The end result is an ideal waterproofing surface.
- After these layers comes rubber bitumen. It is thanks to it that soft materials have high elasticity and strength properties.
- In the center there is a reinforcing base or fiberglass in other words. This material is the basis of the tiles and does not allow them to tear.
- Lay another layer of rubber on top of this layer, and cover it all with mineral powder. Bulk protection gives the entire material resistance to mechanical damage and direct exposure to sunlight, making the product fireproof
Roof pie under soft tiles
The soft roof pie has a somewhat complex structure and for its high-quality arrangement it is necessary to understand the functional tasks of the individual layers. All work must begin with preparatory work. At this stage, the base is carefully examined and in case of any serious deviations from the norms, cosmetic repairs are carried out.
A soft roof pie with insulation has the following structure:
- Vapor barrier layer. It is laid from below in order to prevent moisture coming from below. There is a simple answer to the question of where it comes from. During human life, a certain amount of moisture is released. The most basic example is cooking and writing. The warmed air rises and condenses on the cooler side, so it enters the attic space and can then penetrate the roof pie in the same way. It is worth noting that the presence of even a small amount of moisture in insulation boards reduces its performance by more than half
- Thermal insulation layer. Any material can be used on pitched roofs, but on flat roofs it is better to pay attention to hard types, for example, mineral wool slabs
- Waterproofing layer. In fact, it is no different from vapor barrier and is often made from the same material, but the quality suffers. The main task is to protect the thermal insulation layer from moisture coming in the form of precipitation and condensation
- Lathing. This lumber system allows the load from the overlying layers to be distributed as evenly as possible. As a rule, soft roofs are laid on a continuous sheathing made of OSB boards, moisture-resistant plywood or cut boards
- The lining layer creates soft base and does not allow the sensitive layer of bitumen shingles to receive mechanical damage. It has a dense structure and serves as additional waterproofing and protection from strong gusts of wind.
- The finishing layer is the roofing itself. It gives the structure a finished look and serves as protection from the aggressive external environment.
Manufacturers of roofing materials often provide recommendations for the installation of their products. If you want to achieve maximum performance, listen. An incorrect combination of products will inevitably lead to problems that will appear in the first year of operation, for example, leaks and the beginning of rotting of wooden elements.
Requirements for lathing
Metal roofs have a more rigid surface, therefore, the entire structure will also be highly durable. As for soft roofs, they have problems with this. To ensure good strength properties, a number of special measures must be taken.
A little higher in the article we already talked about the sheathing, or more precisely what materials it should consist of. Now, you need to find out how to build it. This process takes place in just three steps.
- After laying the vapor barrier layer, a counter-lattice must be laid on the rafter legs. Its placement must be strictly parallel to the rafters. As a rule, these elements are made from softwood timber. Its thickness should be 3-4 centimeters. Long nails are used as fasteners
- The counter-lattice is covered with auxiliary boards. They must have a cross-section of at least 150x20 millimeters and be attached perpendicular to the rafters
- The sheathing itself is placed on top of all this. If you have easy access to lumber, you can build it from boards, but it is best to use OSB boards or moisture-resistant plywood. The dimensions of the boards must be selected in such a way that the plane is as flat as possible, otherwise the material laid on top may be greatly deformed, which will lead to leaks
IMPORTANT: When laying OSB boards or moisture-resistant plywood, do not forget about ventilation gaps. A distance of 3-5 millimeters is enough to ventilate the air.
Remember that laying underlay carpet is mandatory. If you skip this layer, the rough surface of the lumber will easily damage your soft covering.
Requirements for waterproofing
A roofing pie for a soft roof must necessarily include high-quality waterproofing. As a rule, it is a rolled material and is laid in strips. It is worth noting that during installation work it should not be stretched; it should be slightly sagging. For good protection, the overlap of the material should be about 15 centimeters.
Today in construction you can find only two materials that can be used in this regard.
- Waterproofing film. The simplest and cheapest insulating material. Polyethylene is used as a raw material, therefore, the strength characteristics of the material are very low, and after prolonged exposure to ultraviolet radiation it becomes even more fragile
- Membranes. This product is a kind of film analogue. The fact is that more advanced polymers are used in its production. The structure of the membranes is significantly different from the cheap analogue. The fact is that its structure has pores similar to funnels. It is thanks to them that the material can pass moisture in only one direction. It's really good material, if you care about the thermal insulation layer. Moisture that gets into the roofing pie can leave it in some way and will not come back. There are also varieties that do not allow condensation to accumulate on the surface of the membranes
If we take into account the experience of some developers, then when installing soft roofs, we can recommend using vapor-permeable products. Please note that they only allow steam to pass through, not water. Their use will eliminate the possibility of condensation appearing in the roofing pie from the air. The fact is that bituminous materials, when heated strongly, contribute to the appearance of moisture from the air, which has a detrimental effect on all components of the roof.
Requirements for roofing pie
The roof pie for soft tiles may differ slightly from the standard set of layers. Some of them are removed from the composition due to their inappropriateness. The following factors may influence this:
- Functional purpose of the building. It can be industrial, residential or commercial
- Frequency of use. In buildings that are used only in warm seasons, it is not advisable to install heating systems; therefore, thermal insulation boards can be removed
- If there is a residential attic in the house, it is imperative to use thermal insulation
- Weather conditions in your region
When installing bitumen roofs, you should use your head as much as possible and take into account the compatibility of the products included in the cake. Never ignore the manufacturers' advice; they often play an important role in installation.
If you have doubts about the materials, ask the seller or friends about them, and in extreme cases, you can turn to specialists.
The construction of a roof under a soft roof is an expensive part of the construction of the entire building, but it is better not to skimp on these layers. If you lay the surface with low-quality materials, then soon you will need repairs, for which you will spend a much larger amount.
