Roof sheathing: what is it and how to do it correctly

One of the tasks of roof sheathing is to strengthen the spatial structure of the roof with its rigidity. The article contains information about the types of lathing, their properties and features. After getting acquainted with the proposed material, you will know how the base structure differs for tiles, slate, ondulin and other finishing coatings.

Main elements of a roofing system Source krrot.net

Lathing: purpose and features

The roof, as part of the structure, plays a dual role - it protects living quarters from the vagaries of the weather, while at the same time being an important decorative element. The construction market offers a wide range of roofing materials that cope equally well with these two tasks. In order for the roof covering to lie correctly and reliably, a lot of preliminary work is done to prepare the base; One of its important parts is the sheathing.

Lathing is usually called a structure that is mounted on top of the rafters (the main, supporting roof system) and is characterized by the following properties:

• Strengthens the roof structure , distributing the load from the roofing material and thereby extending its service life.
• It can take the form of a lattice of lumber (laid in various ways into a category) or continuous flooring , the design is determined by the type of roofing material.

Arrangement methods Source legkovmeste.ru

• Continuous sheathing is required in those areas of the rafter structure that bear the maximum (or, in the winter season, additional) load. As a rule, reinforcement is required for eaves overhangs, valleys, ridges and other places where slopes join.
• Reinforced sheathing is recommended in places where snow guards, stairs, and solar panels are attached.
• It is made from boards (preferably edged and tongue-and-groove), timber, board materials or high-quality plywood . In recent years, profile-type ventilated metal lathing (special thin-walled purlins with holes) has become widespread.
• Roof lathing should be distinguished from counter lathing . The function of the latter is to form a ventilation gap for the waterproofing layer. The counter-lattice is placed on rafters protected by hydrobarrier material.

Roof with counter-lattice Source superarch.ru

Why do you need a sheathing?

Before we talk about sheathing, we need to have a good understanding of the structure of the roof.

Roof: terminological subtleties

A roof is the covering of any building. It protects the inside of the house from precipitation, wind, and temperature changes. The roof consists of two or more slopes - inclined planes, in turn consisting of a rafter structure and sheathing. If there are two slopes, then their horizontal closure is called a ridge, and the edge of the slope protruding above the wall is called an overhang.

The rafter system of the hipped roof is ready for laying the sheathing

Rafters are a load-bearing structure that consists of:

• vertical racks;
• inclined struts;
• rafter legs.

Sheathing is a solid or lattice flooring attached to the rafter legs.

Horizontally oriented sheathing is sewn onto the rafters

The roof is a “pie” consisting of a roof covering attached to the sheathing and underlying layers of insulation, wind and vapor protection.

The roof can be cold (the attic is insulated) and warm (insulation, hydro- and vapor barriers are laid under the sheathing). The latter is, in particular, used for residential attics.

The roofing pie in its most complete configuration requires a complex sheathing design

If you have an attic, you can get by with roofing without thermal insulation; waterproofing is always required.

Purpose of the sheathing

The sheathing performs the following functions:

• serves as the basis for fastening the roof;
• naturally enhances the shape of the slopes and the roof structure as a whole and helps maintain its geometry for many years;
• absorbs and evenly transfers the load from the roofing pie to the rafters (up to 50 kg/m2);
• with the help of a counter-lattice, it prevents the formation of condensation at the border of the cold and warm layers of the roofing pie in the case of a heated attic.

Condensation on the inside of the roof causes rotting of the sheathing, rafters, and wetness, and thereby worsens the thermal insulation qualities of the insulation.

Types of structures

The roof structure provides for one of two types of sheathing - solid or sparse; which one to prefer is decided in each specific case after choosing the finishing coating. Features of these types are characterized by the following parameters:

Continuous sheathing

Moisture-resistant sheet material (FSF or OSB) is laid with a gap not exceeding 1 cm. This indentation makes it possible to compensate for changes in the linear dimensions of the material during operation (with increasing humidity and air temperature, expansion occurs and vice versa).

For arranging a continuous sheathing, it is preferable to choose sheets rather than boards. The advantage of this choice is a perfectly flat surface, free from changes that are inevitable when using boards. A solid base also has some disadvantages:

• Cost . Plywood and board material (OSB) are more expensive than boards, so the construction of such a base will lead to an increase in the construction budget.

Solid plank sheathing Source krysha-expert.ru

• The appearance of condensation . Dense installation makes it difficult for air to circulate under the roof. If a ventilation gap is not provided, moisture will inevitably begin to linger in the roofing pie, which will negatively affect its quality and destroy the insulation (if it is provided).
• Necessity . A solid base is a technological necessity for flexible tiles. For metal tiles, it is more logical to arrange a sparse sheathing; it will be more practical and economical.

Sparse lathing

Regardless of the design features of the roof, the optimal lumber for a sparse structure (for most roofing coverings) is considered to be:

• A block with a cross section of 5x5 or 6x6 cm.
• Board for roof sheathing, 2-4 cm thick.
• Quality . A necessary condition is the choice of wood of at least grade 2. Knots and other defects on low-grade lumber can eventually cause some elements to break under the weight of snow. Another condition is that you should purchase well-dried wood. Raw lumber will certainly begin to deform, and fasteners (nails, screws) will weaken and begin to fall out.

Discharged lathing Source kabanchik.ua
The spacing of the lathing, mounted in disparity, is selected taking into account the selected finishing coating; it varies within fairly narrow limits. This base is suitable for laying ceramic tiles, corrugated slate, and metal tiles.

Antiseptic for wooden sheathing

Even if the roof is impeccable and does not allow water to pass through, the wood in the roofing pie and rafter system is subject to the adverse effects of humidity and temperature changes, which provokes the formation of fungi and mold. Mice and woodworms happily inhabit the roofing pie. Wood is a fire hazard.

To avoid this, you need high-quality impregnation. It must resist all these dangers and penetrate deeply into the structure of the wood, not contain substances harmful to humans (arsenic, copper sulfate), dissolve well in water, and not wash off for a long time.

In our climatic conditions and the conditions of a particular house, we need to choose what is more important - resistance to moisture or fire . Wood is impregnated only once. And the first composition will be the main one in action. Coatings applied in the second and third stages will work weaker.

There are two methods for applying antiseptics.

1. Impregnation is the immersion of wooden elements in a bath or other reservoir with a composition. Usually applied before lumber is sold. But it can also be done at home, for which the manufacturer indicates on the can the required time, which for small and medium-sized lumber is 30–60 minutes, but can reach up to 4 hours.
2. Manual processing - spraying or painting, which saves the composition, but the efficiency is reduced.

   
   Processing lumber manually does not ensure deep penetration of impregnation, but it saves its quantity

An antiseptic is protection against fungus (fungicide), microbes (biocide), insects (insecticide) in one bottle. The composition of a good antiseptic should be completely harmless to humans. Antiseptics for external parts include a coloring alkyd resin.

I can confidently recommend the water-based antiseptic “Senezh”. It comes in different series for different designs - “Ultra”, “Bio”, “Thor”, “Sauna”. We treated the rafters, floor beams, and sheathing with the “Ultra” variety. "Senezh" is easily applied with a spray gun. With a small consumption of the product, only slightly higher than stated (250-300 g/m3), the impregnation by eye turned out to be of high quality and even decorated the wood. The manufacturer promises bioprotection for up to 35 years and a “healing” effect for already damaged wood. About ten years have passed and there is no reason to complain yet.

I did some market research. It showed that, in addition to Senezh, Pinotex Impra and Pinotex Ultra products produced in Estonia are popular, as they are highly effective and have a decorative effect. But unlike Senezh, they cannot be used on wood already affected by microorganisms. And the domestic product “Drevotex” protects from atmospheric influences and the sun, gives a beautiful appearance to the product, but has restrictions on the moisture content of the lumber: it cannot be applied if the humidity is more than 20%.

Table: comparative characteristics and prices of antiseptic impregnations

Photo gallery: several types of antiseptics

"Drevotex" is inferior to "Senezh" both in functions and in efficiency

Pinotex Ultra is considered a rather expensive, but high-quality antiseptic with a wide spectrum of action

"Senezh Ultra" is the most affordable domestic antiseptic

"Senezh Bio" can be used not only for roofing, but also when laying wooden parts in the ground

Pinotex Impra is used for impregnation of hidden structures

About materials

In country house construction, when constructing a base for a finishing coating, the following materials and their combinations are considered suitable:

Sheet (panel) materials

With their help, you can quickly prepare a large area, the resulting base is perfectly flat. When installing the roof, the following materials are used:

• Fiberboard (fibreboard). Board material obtained from wood fibrous raw materials in several ways (may contain resin additives). Products are marked by density and hardness.
• Chipboard (chipboard). The product is obtained by hot pressing a mixture of chips and resin. Plates can have one or more layers and different bending and deformation strengths.

Using sheet materials saves time Source rubankom.com

• OSB (oriented strand board). Multilayer material; In each layer, chips mixed with resin are arranged in a different orientation. This manufacturing feature ensures high practical reliability, due to which OSB sheets most often serve as the basis for finishing coatings.
• FSF . It is obtained by gluing veneer sheets (thin sheets of pine or birch wood). This type of plywood is characterized by high water resistance and wear resistance, which allows it to be successfully used in roofing installations.

Advantages of using sheet materials:

• The best option for soft roofing materials .
• Budget cost.
• The slabs raised onto the roof are easily and quickly installed .

The disadvantages include the following features:

• Plates, like any wooden material, need to be pre-treated with an antiseptic and fire retardant.
• Installation of roof sheathing is carried out in dry weather , otherwise sheets soaked in moisture are likely to become deformed.
• It is not very convenient the slabs onto the roof.

Installation of OSB board Source rodnik-group.ru
See also: Catalog of companies that specialize in roof repair and design.

Board and timber

Lumber, which serves as the main raw material for arranging sheathing. Their characteristics are subject to the following conditions:

• Optimal choice . Edged or tongue and groove board; It is advisable to choose products made from softwood with a moisture content not exceeding 20%. An economical option is a slab, which is laid flat side up.
• It is recommended to use products no wider than 15 cm - wider ones are more susceptible to warping.
• Basic rule of fastening : when organizing a continuous sheathing, leave a gap of 3-5 mm; for sparse sheathing, the fastening step is calculated in advance.
• Fastening elements . Nails are used for fastening to the rafters; their length is selected as twice the thickness of the board (beam).
• For a structure with a wide rafter pitch (more than 80 cm), it is more practical and reliable to replace the roof board with timber (with dimensions from 5x5 cm). For the counter-lattice, take a 3x5 cm beam.

Methods of fastening boards and beams Source plotnikov-pub.ru

• The lumber is not only dried, but also treated to protect it from rot and insect pests.

The advantages of using lumber are their budget cost, environmental friendliness and low weight, which makes lifting them onto the roof easy. The following are considered negative aspects of use:

• Requires professional installation skills .
• Mandatory additional treatment to protect against mold and insects.
• Possibility of deformation in wet conditions. To eliminate this possibility, laying the sheathing and roofing is carried out in dry weather.

How should you secure the rafter system: nails or screws?

We replace the roof on the house ourselves. Masters, how should you fasten the rafter system with nails or screws so that everything is secure?

The rafter system cannot be secured with nails or screws. According to regulatory documents, rafters in places where they are supported by tie rods must be in notches and secured with metal studs. In the upper part, at the joints, the rafters are fastened to each other using wooden plates on both sides. The overlays are attached to the rafters with special screw nails. You should pay attention to the fact that at the junctions of rafters with ties and in the upper joints, a tight fit of the elements to each other must be ensured - gaps between them are not allowed.

When installing a rafter system (there are many components), nails and self-tapping screws, screws and studs, and special fasteners and bolts with nuts are used.

In your case, it is important to decide which specific node of the rafter system you are talking about.

If we are talking about the place where the rafters are attached to the mauerlat, then a groove is selected in the rafters (as an option, there are others).

Next, the rafters are attached with corners to the mauerlat and to the rafters.

A wood self-tapping screw is screwed into the corner, or a screw can be used (these are different things).

Nails were also used, but in our time special fasteners are more often used.

Fasteners include various angles, plates, supports, brackets, etc.

Naturally, it is better to fasten corners and plates with self-tapping screws rather than nails (although they are also used), but you need a screwdriver.

In addition to self-tapping screws (or screws), a bolted connection can also be used,

If the wood is dense, then it is difficult to immediately “drive” the self-tapping screw; it is better to pre-drill a hole with a diameter slightly smaller than the diameter of the self-tapping screw (screw).

When installing a rafter system, nails and screws can be used (among other things that you didn’t ask about), that is, not one type of fastener, but several.

All options are working, be guided by the location, what kind of roof, what kind of load (including not only the weight of the roofing “pie”, but also snow and wind loads), what kind of rafter system, what kind of roofing material, etc.

The rafter system, like the roof as a whole, is a calculated (designed) “unit”, based on the design, and what is best (including fasteners) is selected for a specific roof.

Video description

About the intricacies of roof installation in the following video:

Metal for sheathing

Sheathing made of metal profiles is recommended for buildings with a slope length exceeding 6 m, as well as for buildings with a high level of fire hazard. The metal structure can only be sparse; it is assembled from pipes of a suitable cross-section, channels and I-beams; made of steel (stainless or galvanized). The elements are fastened with self-tapping screws or welding (the latter is possible if the rafter structure also consists of metal elements). Metal roof sheathing has many advantages:

• Dimensional accuracy . The use of a metal frame minimizes mistakes that even professional builders make when installing a complex structure (for example, an attic floor).
• Expanded application possibilities . The design is suitable for arranging roofs of a large area (with long slopes), including for buildings for industrial purposes.

Using a hat profile Source prostanki.com

• Increased strength . The characteristic affects not only the service life, but also the resistance of the system to wind and snow loads.
• Resistance to deformation when changing temperature and humidity.
• Corrosion resistance . The structural parts are coated with modern polymer compounds that reliably protect the metal from moisture.
• Installation of the structure is permitted in any weather conditions .

The obvious disadvantage is the cost of metal sheathing and the complexity of installation work - its installation will require the involvement of specialists with skills in working with metal and welding.

Which board to choose?

Typically, a material such as wood is used to make a high-quality and durable frame structure. The thicker the board in this case, the more durable and wear-resistant the resulting structure will be.

The optimal parameters for the width of the slats in this case are 25-50 mm. However, according to professional builders, 25 mm inch boards are considered the most convenient to use. Narrow parts are used as is, while wider elements can be cut lengthwise to save lumber.

Take a closer look at the surface of the boards - it should be in good condition. There should be no traces of rot, fungus, areas darkened by dampness or splinters on the material. Otherwise, such a frame will not last long, and the roof will not be safe enough.

As a rule, when purchasing, the moisture level of such materials does not correspond to the construction conditions, so it must first be prepared and dried thoroughly. To do this, many people stack the boards on pads for air circulation, and attach a small canopy on top, which is designed to protect the wood from sunlight and precipitation.

Be sure to make sure that all the boards in one package lie neatly and evenly. If you notice unnecessary bends and twisting of materials, then it is better to refrain from purchasing them.

If you want to cut the boards lengthwise, it is recommended to do this as soon as possible. This is explained by the fact that the stress accumulated during drying can lead to deformation of the wood when cutting it.

Most often, to create a base for metal tiles, a board with dimensions of 25 (30) x 100 mm is used. The parameter of its thickness in this case is not so important, but most often it is 25 or 30 mm, since the weight of a metal roof, as a rule, does not exceed 7 kg per square meter. m. Such materials can easily withstand significant loads. The main thing is that their thickness is the same or with small deviations (no more than 2-3 mm). If we take this condition into account, the result will be a correct and even slope plane.

Calculation of the cost of lathing

The calculation of the sheathing is included in the general calculation of the roof; it is carried out on the basis of initial data - roof parameters, design features of the rafter system, construction materials and roofing. There is a selection of calculators on the Internet that allow you to get average figures for the cost of the project (the more complex the roof, the more approximate the figures will be).

To calculate the sheathing, it is proposed to enter its characteristics: the width and thickness of the board, as well as the distance between the boards. But for this you need to have preliminary calculations, which take into account not only the cross-section of the board or beam, but also other parameters, including the type of sheathing.

In order for the planning of the required amount of materials to be accurate, it must be carried out by a specialist who can take into account all the variables and specifics of roofing materials. The quality of fastening of the finishing coating depends on how accurately the calculation is carried out and the pitch of the load-bearing part is selected.

An important part of the roofing pie Source qopudin.bilagyteco.ru.net

How much does the sheathing cost?

I found it difficult to calculate the average cost of materials in our study. There are too many variables: the cross-section of boards and timber and their quantity depend on the design of the sheathing, the material and the area of ​​the roof. There are many calculators on the Internet: when you enter all the data, you get the price. I recommend the StroyDay website calculator - in my opinion, it is the most balanced and complete.

Using the calculator from the StroyDay website, you can calculate both sparse and continuous sheathing

In the same way, I can only give average figures for the cost of work by professional craftsmen in terms of per square meter.

Table: cost of installation of sheathing

The influence of roofing on the sheathing arrangement

The correct roof sheathing is always designed taking into account the properties of the selected finishing coating; it also specifies the type of load-bearing part and determines the installation rules.

Slate

Asbestos-cement slate (flat or corrugated sheets) has been one of the most popular roofing coverings for decades, due to its low cost, ease of processing and durability. The sheathing pitch when calculating a slate roof is selected individually; it is influenced by the thickness of the sheet and its linear dimensions; it varies from 50 to 75 cm. The cross-section of the beam ranges from 5 to 8 cm. Regardless of other parameters, the following rule is observed during installation: three beams serve as support for each sheet. This is enough to maintain the rigidity of the roof under any load (movement of a person or snow cover).

Professional recommendation

In practice, sometimes there are situations when, for one reason or another, the upper planes of the sheathing do not lie on the same line. For metal tiles, these are unacceptable deviations; they must be eliminated; the process can be accelerated using a simple measuring device. How to make it?

Step 1

. Cut a wedge 30–40 cm long from the board, make it in the form of an equilateral triangle with an acute angle at the apex.

Step 2

. Find a piece of roofing felt; it is recommended to place it under the sheathing during leveling. Not only does it not deteriorate its original properties throughout the entire period of operation, but it also interrupts possible routes of moisture entering the wood. Cut the roofing felt into rectangular pieces with sides approximately 2x4 cm.

Step 3

. Place the wedge on a flat surface, and one piece of roofing felt on both sides. Slowly move the level slat from the base of the wedge to the top. It is necessary to determine the place where the movement will stop - pieces of roofing felt will not allow it. Mark on the wedge the distance from the top to the fixed position.

Step 4

. Add another piece of roofing felt on each side and repeat the above steps, make a second mark.

Using this method, determine the total thickness of 5-6 pieces of roofing material one by one, and cut the marks for each. For ease of use, transfer them to the back side of the wedge. The device is ready, working with it is very simple. First you need to determine which sheathing boards require adjustment. This is done using a long level, a rule, or any level slats. Then a wedge is inserted into the gap, the marks on it indicate how many pieces of roofing felt a particular board needs to be raised.

In conclusion, we remind you once again that the reliability, duration, efficiency and safety of operation of the entire roof depends on the correct arrangement of the sheathing; carefully follow existing construction technologies and rules. Don't experiment; mistakes are very costly.

Is it worth doing it yourself?

You can do the installation of the sheathing yourself, but it is not easy, especially for a beginner in the field of construction. You need to have certain tools, plan and prepare everything correctly. It is important to have theoretical knowledge and skills in carrying out repair and construction work. It is advisable to have an assistant. Self-manufacturing and installation of such a design will save money. But, if you lack self-confidence and tools, then it is better to turn to professionals. After all, there is a risk of making gross mistakes, as a result of which the roof will soon have to be redone.

Criterias of choice

The choice of lathing is based on a competent calculation, taking into account all the features of the roof structure. These calculations help to find the optimal material for its manufacture, the required cross-section and the distance between its elements. The following criteria influence the choice of design:

• Roof slope angle. The greater the slope, the less snow accumulates on the roof surface, which means less load on the rafter frame, due to which the pitch between the sheathing elements can be increased.
• Type of roofing. If the material has a rigid shape and does not deform during operation, then sparse or lattice lathing is used for its installation, since it requires minimal support. Soft coverings, on the contrary, are laid on a solid base.
• Climatic conditions. If construction is carried out in a region with snowy winters, then the sheathing should be reinforced with additional elements so that it is able to withstand additional loads during snowfalls.

Remember that the installation of the sheathing is carried out after installing the rafter pairs, when their upper ribs are aligned with the building level and are in the same plane, otherwise the roof will turn out crooked.

The choice of lathing depending on the roofing material

Selecting the sheathing pitch

Counter-lattice for metal tiles

The purpose of the counter-lattice under metal tiles is to create a gap for the passage of air in the under-roof space. The structure is mounted on top of the waterproofing, resulting in an open space for air.

Is a counter-lattice needed for metal tiles?

The advantages of the counter-lattice are as follows:

It follows from this that installation of counter-lattice under metal tiles is mandatory. The design, in addition to the listed positive aspects, allows you to correct irregularities that were made during the construction of the rafter system.

Counterbeam thickness

Basically, timber with a cross-section of 30x50 mm and a length of 135–137 cm is used to install counter-lattice. Such lumber is used for the construction of a simple roof. If a sloping roof is being erected, the cross-section must be increased to 50x50 mm. The distance between the counter-lattice elements along one rafter leg should not exceed 30 cm.

Installation instructions

Having prepared the bars of the required size, you can begin installation, which is performed in the following order:

Approximate consumption of nails for flexible tiles

The number of fasteners depends on the slope of the slope. For steep roofs (more than 45 degrees), additional nails are driven in to improve the quality of fixation. The number of layers of soft tiles also affects consumption. Single-ply shingles require fewer fasteners, while multi-ply shingles require more.

How many nails are needed to attach one module using the TechnoNIKOL bitumen shingles as an example?

The official instructions from Technonikol indicate that on average, about 80 g of roofing nails are required per 1 m2. To calculate, the roof area is multiplied by this mass to get the overall result. If the roof has an area of ​​90 sq. m, it turns out: 90*80=7200 g, which is equivalent to 7.2 kg.

What are barbed and screw nails and how do they work?

For sheathing construction, rough nails are an excellent choice. And the strength properties of this fastener exceed those of self-tapping screws.

Only screw nails can compete with this. They also have notches, but they look like a drill. So when you drive a nail like this, it rotates and screws into the wood.

The most common mistakes

Although laying the sheathing is not super complicated, gross violations are often committed during its installation:

• the use of low-quality lumber having different thicknesses and incorrect geometry;
• the pitch of the sheathing is uneven or does not correspond to the profile of the metal tile;
• lack of counter-lattice, which does not directly affect the quality of installation, but subsequently leads to rapid rotting of wooden structures.

You cannot lay metal tiles over old slate flooring. It is necessary to dismantle it and reinstall the boards with a different step. It is also advisable to use nails rather than self-tapping screws, which can quickly break.