How to properly make a roof under a soft roof. Types of lathing for soft roofing and load calculation. Requirements for sheathing under bitumen shingles

In our country, one of the most popular roofing materials is soft tiles. Its advantages include low cost, light weight, durability and ease of installation. In general, this type of coating can be divided into two types: roll materials, among which, for example, roofing felt and bitumen shingles. Their main difference is the form of manufacture. In order for the roof to be strong and reliable, the roofing materials should be properly secured to the main elements. For this purpose, a special sheathing is created, which can be sparse or solid. In the case of a soft roof, the design features of which we will discuss in this article, both types can be used.

Knowing the design features, you can easily make the sheathing yourself

The roof must withstand any static loads. The thickness of the base will depend on the pitch of the rafters, and the thickness of the formwork will depend on the type of material that will be used. The sheathing should not have any play, so it must be secured especially carefully. If bitumen shingles were chosen, the backing should be installed in two passes. It is very important that there is no corner or sharp bend in the structure, as this can lead to deformation of the entire roof.

What is it made of?

Typically, the sheathing for a soft roof is a flat surface created from edged boards. You can also use OSB board or plywood.

It is not recommended to use a board that is cut in half or not cut at all. A mistake like this can cost you a second roof re-roofing.

Each of these materials has its pros and cons. For example, OSB board It is light in weight and durable, inexpensive, but is characterized by questionable environmental friendliness and poor vapor permeability. Plywood is not subject to deformation and has good moisture resistance, but is flammable and can emit harmful substances. As for edged boards, this material is very easy to install and environmentally friendly, the only negative is the possibility of rotting. However, this drawback is easily eliminated by treatment with special substances.

Carefully check the degree of dryness of the material

Regardless of what material you choose, it is important that the humidity level does not exceed 20%.

The best material for lathing - calibrated boards. This is explained by the fact that only they can make a perfectly flat surface. To improve waterproofing and thermal insulation properties, diffuse film is used. And roofing fittings will help make the roof even more durable.

It is better to use coniferous wood for boards.

To make the sheathing, you will need a screwdriver, a hammer, Circular Saw, level, pencil and tape measure.

Pitch and other design requirements

The structure must be made in such a way that it can easily support the weight of the roofing material. The type of flooring should be determined taking into account the angle of inclination of the roof. If this angle is up to 10⁰, the flooring will be continuous. If the angle is 10-15⁰, a timber with a diameter of 45x50 mm is used, as well as moisture-resistant plywood. Rafter step in in this case will be equal to 450 mm and directed parallel to the cornice. When the angle of inclination is greater than 15⁰, a similar beam is used, but the rafter pitch should be 600 mm. Where the ridge and valley are located, it is necessary to use an additional beam.

Calculation

Use this table for ease of calculation

Installation instructions

Following the recommendations will allow you to complete the job correctly

All work must be carried out in strict sequence. First you need to attach it to load-bearing structure roofing bars and sheathing. It is important to carry out the work from below, gradually moving upward. Then the bottom sheathing is nailed, which is secured to the cornice board. This is necessary for reliable fixation of the first row of soft roofing. The next step is laying the roofing tape. It should be located horizontally relative to the ridge. The first strip is located at the cornice, the next ones are installed overlapping. To create optimal ventilation gaps, it is important to fix the tape between the counter-lattice bars and the rafters.

Focusing on the edge of the rafters, the first block is fixed. The second one must be placed behind the edge of the first one, while the distance between them is strictly maintained - 30–35 cm. The next bars are fixed in increments of 37 cm, and the last one is installed at the ridge board. You can use regular nails for this job. The distance between them is 20 cm. Using a level, check the correct installation of the bars; they should all be mounted horizontally.

Video: Installation of sheathing

Thus, the quality of the soft roof flooring will depend on the competent creation of ventilation gaps, preparation of the roof, laying of the underlayment, but the most important factor will be the sheathing. Pay attention to its design and installation Special attention. Choose only quality Construction Materials. Carefully study all the nuances, and only then get to work.

Bituminous shingles in last years has become one of the most popular roofing coverings, thanks to its original appearance, imitating classic ceramic tiles. Simple technology fixing shingles with a self-adhesive layer makes it easier self-installation material, but before starting installation work The roof structure requires thorough preparation. In this article we will tell you how the device is made roofing pie under soft tiles.

Soft roofing is called bitumen shingles, which are made from fiberglass or polyester impregnated with a modified petroleum bitumen or synthetic rubber. External surface The shingles are sprinkled with basalt or mineral chips to give color, texture and mechanical strength to the material. Soft tiles are produced in the form of tiles with a figured edge, the length of which is 100 cm, width 30-45 cm, and thickness 0.3-0.45 mm. This roofing has the following features:

A light weight. Square meter soft roof weighs no more than 13 kg, which allows not to make the device heavier rafter frame additional elements.
Flexibility. The material has high elasticity and flexibility, so it can easily be installed on roofs of complex shapes.
Durability. The service life of a roof with such a coating is up to 70 years, and it does not require special maintenance.
Resistance to factors external environment. Soft roofing is valued for its high moisture resistance, tolerance to ultraviolet radiation and temperature changes.

Note! It is not recommended to install soft roofing on structures with a high risk of fire, as it is a flammable material. To reduce the likelihood of fires, the installation of the rafter frame is carried out with mandatory treatment with fire-retarding agents.

Nuances of work

The soft roof is fixed to the base using a self-adhesive layer of low-melting bitumen on the underside of the material, protected by a polyethylene protective film. The construction of a roof made of bitumen shingles can only be carried out under certain weather conditions:

The ambient air temperature should not be lower than 5-10 degrees, since otherwise the bitumen layer will have to be heated forcibly using construction hair dryer or gas burner, risking damage to the tiles.
The ambient temperature should not exceed 25 degrees, so that when installing the roof, the bitumen layer does not melt and flow down the slope.
performed in dry, non-rainy weather on a dried base to prevent rotting of the rafter frame and finishing coating during operation.

Important! Roof shingles should be stored in a dry place, protected from direct sun rays place to prevent melting of the bitumen adhesive layer. Remove from shingles protective film To avoid sticking of the material before installation of the coating, it is not recommended.

Foundation requirements

The installation of a soft roof begins with the preparation of the base, the strength and reliability of which determines the service life and moisture resistance of the structure. The process of creating a roofing pie under bitumen roof must be performed strictly in accordance with technology. The base provides the following conditions for flexible tiles:

Mechanical strength. A soft roof is laid exclusively on a continuous sheathing, since it is not capable of holding its shape on its own. Therefore, the base for installing the coating is made from sheets of moisture-resistant plywood or particle board.
Smoothness. Bottom surface flexible roofing easy to damage, so installation is carried out on underlay carpet However, the base does not interfere with sharpening and freeing it from knots and nicks.
Smooth surface. Installation of a roof made of bitumen shingles does not tolerate curvature. Any misalignment of the sheathing will result in gaps between the shingles.
Ventilation. The ventilation gap between the bituminous tile roofing and the rafter frame must be at least 50 mm to avoid “ greenhouse effect"and the appearance of condensation.

Please note that the compliance of the base the right technology guarantees long term operation of the roof, absence of leaks and mechanical damage to the frame.

Preparation technology

The roofing pie, with which a soft roof is installed, consists of a layer of vapor barrier, insulation, waterproofing, counter-lattice, sparse lathing, lining carpet and finishing coating. The quality of the design depends on the correctness of the calculation, sequence and compatibility of materials. Preparing the roof for soft tiles is as follows:

First of all, it is necessary to check the condition of the rafter frame. All rotten elements must be replaced. Re-treat with fire retardant and antiseptic.
Fix vapor-permeable membrane waterproofing on top of the rafters with overlapping strips. Waterproofing material fixed with a construction stapler with sagging to avoid rupture in case of leakage.
Counter battens 3-4 cm thick are nailed on top of the waterproofing to ensure ventilation gap. Then, perpendicular to the rafters, a sparse sheathing of edged boards is fixed in increments of 30-50 cm.
Sheets of plywood or OSB are nailed onto the additional sheathing, leaving a gap of 1-3 mm between them.
An underlay carpet is laid on a solid base, on which it is subsequently laid soft roof.

Experienced craftsmen note that installing a high-quality, reliable base makes a bitumen roof more durable and resistant to mechanical damage. Therefore, during the work process, you must strictly follow the technology and recommendations of the manufacturers.

Video instruction

The reliability of a roof covered with soft tiles is ensured by correct design sheathing bases. Of course, it is no secret that it must be solid, moisture-resistant, smooth, unbending, and have a surface free of nicks and chips. But practice shows that the correctly selected material for the frame is not enough; it is also necessary to master the intricacies of installation technology and know how to properly attach the sheathing.

Sheathing for soft tiles: device options

There are several basic technologies for installing lathing. The simplest of them is a continuous sheathing under bitumen shingles, which is laid directly on the rafters. This technology is not used very often due to its lack of efficiency. Much more common is the method in which beams or boards are first secured to the rafters at an angle or parallel to the ridge, and then plywood or OSB is installed on them.

According to another method, it is attached to counter-lattice beams, which are fixed to the rafters, parallel to the rafters. Thanks to this base, a ventilation gap is formed under the continuous sheathing, starting from the eaves. The air, “enriched” with moisture, is discharged outside through the ridge. This makes it possible to support optimal humidity cover sheathing and other wooden roof elements and protect them from rotting and other damage. This type of configuration also makes it possible to install a layer of insulation and a superdiffusion membrane laid on the rafters.

There is another significant point, if the lathing is under flexible tiles will be installed with errors, then the manufacturer of the roofing material, despite the flaws in the roofing surface, has the right to refuse to fulfill warranty obligations.

Which material to choose

Roofing plywood
Waterproof plywood is one of the most common materials for continuous sheathing. It is moisture resistant and flexible. To these characteristics it is also worth adding the multi-layer coating in order to understand what determines the high functional qualities of such lathing and its long service life.

The optimal type of plywood used for sheathing is FSF plywood. She -

made from coniferous trees;
has high strength, including bending strength;
moisture resistant;
resistant to aggressive environments;
has a relatively light weight;
Thanks to treatment with special compounds, it has fairly good fire-resistant and antiseptic properties.

OSB-3 boards
By structure OSB boards fundamentally different from plywood or chipboard. Computerization technological process pressing minimizes the variation in thickness of OSB, so lathing under bitumen shingles from these slabs is very effective. They -

moisture resistant;
do not deform, do not warp from moisture;
sufficiently resistant to snow and wind loads;
are light in weight;
form a smooth, perfectly flat surface.

To install the frame under a soft roof, tongue-and-groove or edged boards from coniferous trees, sorted by thickness, are also used. , whose humidity does not exceed 20%.

Sheathing for flexible tiles: proper installation

When installing it, it is necessary to completely eliminate the possibility of sharp breaks and corners, otherwise excessive bending and friction of the roofing material cannot be avoided.

IN mandatory the materials used to construct the sheathing for soft tiles are adjusted - all its lines must be smoothed as much as possible and made “soft”.

When using an edged board, the sheathing pitch for flexible tiles should be 3–5 mm. The boards are laid taking into account the direction of the fragments of the annual rings. They should be directed with their bulges upward. Why is this so important? If it is “driven”, the board will begin to unbend and, filling the gap between the slats, will have minimal impact on the roof. Otherwise, the arching will form a “hump,” which will completely disfigure the roof surface.

As an additional measure, it is better to fasten the wet board with two screws on each side.

The plywood is laid with the longitudinal side parallel to the ridge.

It is very important that the joining seams do not become a continuation of each other.

When installing in the cold season, the gap between OSB-3 boards, as well as plywood sheets, must be left at least 3 mm to compensate linear expansion in a warm place.

Fastening of plywood sheets is carried out using rough nails or self-tapping screws. The caps of the fasteners are completely recessed to protect top coating from damage. Fastening is carried out approximately in increments of 15 cm with the obligatory fastening of the edges of the sheets.

The category of materials referred to as soft roofing includes several commonly used coatings. These include roofing felt, soft bitumen shingles, and several types of built-up roll materials. They are all different from each other appearance and characteristics, but their production is based on one component - modified bitumen. It is he who gives roofing coverings the same flexibility and softness. The material itself does not have a rigid shape, so a strong and rigid sheathing is needed under it, which will withstand external loads. In this case, the soft roof will only provide protective and decorative properties.

Types of sheathing for soft roofing

If we talk about the sheathing as a whole, then it comes in two types: sparse and solid. The first is assembled from boards or bars, between which gaps are left or, as they are also called, installation steps. The second is a continuous flooring without gaps. For soft roofing, it is the second option that is used, because when laid on a loose sheathing, soft roofing materials will sag between its elements.

A continuous sheathing is made under the soft roof, otherwise the material will sag in the cracks between the boards

Sheets of moisture-resistant plywood, OSB boards and boards are used as flooring for continuous sheathing. The latter must be either edged or tongue-and-groove coniferous species wood As for moisture-resistant plywood, it must be chosen correctly by brand, because there are two positions on the market with this name:

FC, which is recommended for use only for finishing interior spaces.
FSF, which is used for both internal and external installation.

For continuous sheathing, FSF is suitable. This material is made from several layers of veneer (from 3 to 21), which are glued together special composition based on phenol-formaldehyde resins. It should be added that during the production process plywood FSF Each layer is first treated with bakelite varnish, so the material has high strength and water resistance.

As for OSB, for the lathing you also need to choose a waterproof modification, i.e. grades OSB-3 and OSB-4. The latter is intended for structures that are subjected to maximum loads at high humidity air, so it is quite expensive. For roofs, you can use OSB-3 plywood, which is not inferior in moisture resistance to the fourth model.

When assembling the flooring, you can leave a small gap between the elements, the size of which should not exceed 1 cm. It is called compensation because it will compensate for the expansion wooden products due to changes in humidity and temperature.

Types of continuous sheathing

The sheathing for a soft roof can be single or double. In the first case, boards or panels are laid directly along the rafters. In the second, a sparse sheathing is first installed, and a solid one is installed on top of it. The second option is preferable because there is space between the two layers, which is used for roof ventilation. And this makes it possible to take away wet vapor air that rises from the interior of the house. It is they that on uninsulated roofs cause the formation of ice and condensation on the rafter system.

But this is not the only criterion for choosing double flooring. Much will depend on the angle of the roof slopes.

When the slope is inclined 5–10°, a single-layer flooring can be used.
In the range from 10 to 15°, a double sheathing is laid with a step between the lower elements of 45–50 cm. For the lower sheathing, it is better to use bars with a section of 50x50 mm.
If the slope angle exceeds 15°, then the installation step can be increased to 60 cm.

In principle, you can increase the pitch of the bottom sheathing up to 100 cm, depending on the size of the lumber used for it. For example, if a board 40 mm thick and 120 mm wide was used for this. The smaller the cross-section, the smaller the pitch, and vice versa. For each material, its own step is selected relative to its thickness.

Table: ratio of the spacing of the sparse sheathing to the thickness of the solid flooring elements

How to calculate the amount of material for lathing under a soft roof

Taking into account the above-mentioned relationships between the spacing of the sheathing elements and their thickness, it is possible to make quite exact calculation this design. To do this, you will have to first take the dimensions of the roof itself, which are indicated in the building drawing. And if the roof is a complex multi-level and multi-slope structure, then it needs to be divided into simple geometric figures. It is on their basis that the total roof area is calculated.

In this case, you will have to take into account the angle of inclination of each slope, because the smaller the angle, the greater the loads the sheathing system is subjected to. This means that you will either have to reduce the spacing of the boards or bars, or increase the thickness of the slab and sheet flooring. Therefore, to simplify calculations when determining the total roof area, correction factors are used. For example, when the slope is inclined at 35°, a multiplying factor of 1.221 is used.

Calculation of a solid structure

With the calculation of a continuous sheathing, the situation is simpler, because it covers the entire area of the slopes. That is, its area will be equal to the area of the roof. Let's look at an example of calculating the number of plywood sheets for a slope with an area of 50 m².

In the construction business, when calculating the amount of building materials, a small reserve is made in the range of 5–10%. Here we need to do the same, so the final result is 23–24 sheets.

The number of OSB boards is calculated in exactly the same way. But with boards it’s a little more complicated. First of all, you need to calculate the area of one selected board. Length edged boards varies in the range from 1 to 6.5 m in increments of 0.25 m. Width - in the range of 75–275 mm in increments of 25 mm.

Let’s say a board 3 m long and 0.1 m wide is used for the sheathing:

We calculate the area of one board: 3∙0.1=0.3 m².
A slope with an area of 50 m² will require 50:0.3= 166.66 boards.
Round to the nearest whole number and add a margin of 10%: 167∙1.1 = 184 boards.

Calculation of sparse sheathing

For this calculation, the area of the slope itself is not required. The length of the roof and its height are required, that is, the distance from the overhang to the ridge.

Rules for installing sheathing under a soft roof

Regardless of whether one- or two-layer sheathing is used on the roof, the main requirement for the design is a smooth and durable surface without defects and flaws in lumber. That is why when using boards, calibrated material is selected.

According to construction canons, the rafter system is aligned along the slopes in one plane, so you need to be sure that the ends rafter legs already exhibited. This means that we can assume that the boards, plywood or OSB boards being laid will lie in the same plane.

The sheathing elements must be joined along the rafters. A board protruding beyond the rafters will not provide strength when installing roofing material

You need to start installation from the cornice, or more precisely, from the lower ends of the stops. The boards are selected in length so that two adjacent elements are joined on one rafter beam. If this fails, you will have to trim them, which will increase the amount of waste. The same goes for sheets and slabs.

The boards are laid with a small gap of 1 cm and attached to the rafters with nails or self-tapping screws. It is better to fasten from the end side. If screws or nails are installed on the front side, then their heads must be driven into the body of the lumber to a depth of 0.5 mm. In this case, on each rafter it is necessary to nail two fastening elements- one on each edge.

Plywood sheets or OSB boards on the roof as a continuous sheathing should be laid staggered with an offset of a third or half of the panel

Concerning flat materials for sheathing, they are placed offset relative to each other by a third or half a sheet. This is done so that the loads acting on the continuous sheathing are evenly distributed over its entire surface. In this way, the panels are laid perpendicular to the rafters. Plywood with dimensions of 1.5x2.5 m can be installed along the rafters. In this case, you will have to take into account that the sheet material itself cannot bear large loads, so at least three rafter legs must fall under it: one exactly in the middle and two at the edges. But here, too, you will have to take into account that two adjacent plywood sheets must be joined on one rafter. A gap between them (3–5 mm) is mandatory.

Plywood and OSB are fastened with galvanized self-tapping screws or ruff nails around the perimeter every 10–15 cm and along the entire plane along the rafters in checkerboard pattern. It is these fasteners that need to be used, because they can withstand the stresses that arise in OSB boards or plywood sheets due to changes in humidity and temperature.

The procedure for laying flat panels on a discharged sheathing:

A string is stretched along the edges of the rafters, defining the boundary of the roof overhang. It is tied to two self-tapping screws, which are screwed into the two outer rafters located on different parts roofs.
The first sheet is laid along the outer edge of the first rafter leg, while its adjacent edge must accurately follow the twine.
The first sheet of continuous sheathing is laid strictly along the edge of the rafter leg
The first sheet is fastened with self-tapping screws 50 mm long along the rafters in increments of 20–30 cm.
The bottom row is assembled in this way.
The bottom row is laid with the panels joining on the rafters
The next row starts with half a sheet, so one panel must be cut in half.
The half is attached to the rafters, like the whole sheets, with the same screws with the same pitch.
The second row of continuous sheathing begins with half of the slab, so that the following elements are attached at intervals from the first row
Then whole sheets are used.
The third row begins to be assembled from a single slab.

Video: how to properly lay boards as sheathing elements

Continuous sheathing over open sheathing

In principle, there are no serious differences from the above installation technology No. Simply a solid structure is laid on boards, which are placed on the rafters with a certain distance between the rows. No boards are used to create a continuous flooring. Plywood or OSB is being installed. At the same time, all the above-described requirements are preserved both in terms of the installation scheme of the panels and in the method of their fastening.

Counter-lattice for soft roofing

To insulate the roof, it is necessary to lay thermal insulation material between the rafters. From the outside attic space it is closed with a vapor barrier membrane, and on the side of the sheathing - waterproofing film. You cannot immediately lay the sheathing and make flooring from OSB boards or plywood sheets. Need to create ventilation duct, which will remove moist air vapor from under the roof space. Therefore, bars with a cross section of 50x50 mm are laid along the rafters. This is the counter-lattice, and the space between the waterproofing and the solid flooring is the ventilation gap.

The process of assembling an insulated roof structure consists of the following steps.

From inside the future attic, insulation is laid between the rafters. The main requirement for installation is tight pressing thermal insulation material to the planes of the rafter legs so that cold bridges do not form.
The insulation is placed in the space between the rafter joists so that there are not even minimal gaps left
Placed on top of the insulation vapor barrier film, which is attached to the rafters with metal staples using a stapler. The film is laid in rows with an overlap of 10–12 cm. The joint must be covered with self-adhesive tape.
The vapor barrier film is laid with an overlap and secured with staples
Next, the work is transferred to the external part rafter system, where it fits on top of the legs waterproofing membrane in exactly the same way as the vapor barrier from below. Laying should begin from the bottom of the cornice.
Counter-lattice elements are installed and fastened along the rafters, for which wood screws 70 mm long are used. The fastening pitch is 40–60 cm.
To create a ventilation gap, bars are attached along the rafters, onto which horizontal sheathing is laid.
Lathing elements - boards - are installed across the counter-lattice. They are attached with self-tapping screws 50 cm long.
Installed and fastened on top of the sheathing in a checkerboard pattern plywood sheets or OSB boards. The fastener pitch is 20–30 cm.

Typically, this design is used if there is no sparse sheathing on the roof, or it is assembled from boards 20–25 mm thick. Such a gap will not be sufficient for effective removal of moist air.

Video: rules for laying continuous sheathing on the roof

Continuous sheathing for soft roofing material- the only way to guarantee the quality of the final result. Minimum gaps will not reduce it, but fulfilling the basic requirement - the formation of a flat and durable surface - will create conditions under which the soft roof will last its warranty period.

The category of materials referred to as soft roofing includes several commonly used coatings. These include roofing felt, soft bitumen shingles, and several types of fused rolled materials. They all differ from each other in appearance and characteristics, but their production is based on one component - modified bitumen. It is this that gives roofing coatings that very flexibility and softness. The material itself does not have a rigid shape, so a strong and rigid sheathing is needed under it, which will withstand external loads. In this case, the soft roof will only provide protective and decorative properties.

Types of sheathing for soft roofing

A continuous sheathing is made under the soft roof, otherwise the material will sag in the cracks between the boards

Sheets of moisture-resistant plywood, OSB boards and boards are used as flooring for continuous sheathing. The latter should be either edged or tongue-and-groove from softwood. As for moisture-resistant plywood, it must be chosen correctly by brand, because there are two positions on the market with this name:

FC, which is recommended for use only for interior decoration.
FSF, which is used for both internal and external installation.

For continuous sheathing, FSF is suitable. This material is made from several layers of veneer (from 3 to 21), which are glued together with a special composition based on phenol-formaldehyde resins. It should be added that in the production process of FSF plywood, each layer is first treated with bakelite varnish, so the material has high strength and water resistance.

As for OSB, for the lathing you also need to choose a waterproof modification, i.e. grades OSB-3 and OSB-4. The latter is intended for structures that are subject to maximum loads at high air humidity, and therefore is quite expensive. For roofs, you can use OSB-3 plywood, which is not inferior in moisture resistance to the fourth model.

When assembling the flooring, you can leave a small gap between the elements, the size of which should not exceed 1 cm. It is called compensation because it will compensate for the expansion of wooden products due to changes in humidity and temperature.

Types of continuous sheathing

The sheathing for a soft roof can be single or double. In the first case, boards or panels are laid directly along the rafters. In the second, a sparse sheathing is first installed, and a solid one is installed on top of it. The second option is preferable because there is space between the two layers, which is used for roof ventilation. And this makes it possible to remove moist air vapors that rise from the interior of the house. It is they that on uninsulated roofs cause the formation of ice and condensation on the rafter system.

But this is not the only criterion for choosing double flooring. Much will depend on the angle of the roof slopes.

When the slope is inclined 5–10°, a single-layer flooring can be used.
In the range from 10 to 15°, a double sheathing is laid with a step between the lower elements of 45–50 cm. For the lower sheathing, it is better to use bars with a section of 50x50 mm.
If the slope angle exceeds 15°, then the installation step can be increased to 60 cm.

Table: ratio of the spacing of the sparse sheathing to the thickness of the solid flooring elements

How to calculate the amount of material for lathing under a soft roof

Taking into account the above-mentioned relationships between the spacing of the sheathing elements and their thickness, it is possible to make a fairly accurate calculation of this structure. To do this, you will have to first take the dimensions of the roof itself, which are indicated in the building drawing. And if the roof is a complex multi-level and multi-slope structure, then it needs to be broken down into simple geometric shapes. It is on their basis that the total roof area is calculated.

Calculation of a solid structure

The number of OSB boards is calculated in exactly the same way. But with boards it’s a little more complicated. First of all, you need to calculate the area of one selected board. The length of edged boards varies from 1 to 6.5 m in increments of 0.25 m. Width ranges from 75–275 mm in increments of 25 mm.

Let’s say a board 3 m long and 0.1 m wide is used for the sheathing:

We calculate the area of one board: 3∙0.1=0.3 m².
A slope with an area of 50 m² will require 50:0.3= 166.66 boards.
Round to the nearest whole number and add a margin of 10%: 167∙1.1 = 184 boards.

Calculation of sparse sheathing

For this calculation, the area of the slope itself is not required. The length of the roof and its height are required, that is, the distance from the overhang to the ridge.

Rules for installing sheathing under a soft roof

According to construction canons, the rafter system is aligned along the slopes in one plane, so you need to be sure that the ends of the rafter legs are already aligned. This means that we can assume that the boards, plywood or OSB boards being laid will lie in the same plane.

The sheathing elements must be joined along the rafters. A board protruding beyond the rafters will not provide strength when installing roofing material

The boards are laid with a small gap of 1 cm and attached to the rafters with nails or self-tapping screws. It is better to fasten from the end side. If screws or nails are installed on the front side, then their heads must be driven into the body of the lumber to a depth of 0.5 mm. In this case, on each rafter, two fasteners must be nailed to the board - one on each edge.

Plywood sheets or OSB boards on the roof as a continuous sheathing should be laid staggered with an offset of a third or half of the panel

As for flat materials for sheathing, they are placed offset relative to each other by a third or half a sheet. This is done so that the loads acting on the continuous sheathing are evenly distributed over its entire surface. In this way, the panels are laid perpendicular to the rafters. Plywood with dimensions of 1.5x2.5 m can be installed along the rafters. In this case, you will have to take into account that the sheet material itself cannot bear large loads, so at least three rafter legs must fall under it: one exactly in the middle and two at the edges. But here, too, you will have to take into account that two adjacent plywood sheets must be joined on one rafter. A gap between them (3–5 mm) is mandatory.

Plywood and OSB are fastened with galvanized self-tapping screws or ruff nails around the perimeter every 10–15 cm and along the entire plane along the rafters in a checkerboard pattern. It is these fasteners that need to be used, because they can withstand the stresses that arise in OSB boards or plywood sheets due to changes in humidity and temperature.

The procedure for laying flat panels on a discharged sheathing:

A string is stretched along the edges of the rafters, defining the boundary of the roof overhang. It is tied to two self-tapping screws, which are screwed into the two outer rafters located on different edges of the roof.
The first sheet is laid along the outer edge of the first rafter leg, while its adjacent edge must accurately follow the twine.
The first sheet of continuous sheathing is laid strictly along the edge of the rafter leg
The first sheet is fastened with self-tapping screws 50 mm long along the rafters in increments of 20–30 cm.
The bottom row is assembled in this way.
The bottom row is laid with the panels joining on the rafters
The next row starts with half a sheet, so one panel must be cut in half.
The half is attached to the rafters, like the whole sheets, with the same screws with the same pitch.
The second row of continuous sheathing begins with half of the slab, so that the following elements are attached at intervals from the first row
Then whole sheets are used.
The third row begins to be assembled from a single slab.

Video: how to properly lay boards as sheathing elements

Continuous sheathing over open sheathing

In principle, there are no serious differences from the installation technology described above. Simply a solid structure is laid on boards, which are placed on the rafters with a certain distance between the rows. No boards are used to create a continuous flooring. Plywood or OSB is being installed. At the same time, all the above-described requirements are preserved both in terms of the installation scheme of the panels and in the method of their fastening.

Counter-lattice for soft roofing

To insulate the roof, it is necessary to lay thermal insulation material between the rafters. From the attic side it is covered with a vapor barrier membrane, and from the sheathing side - with a waterproofing film. You cannot immediately lay the sheathing and make flooring from OSB boards or plywood sheets. It is necessary to create a ventilation duct that will remove moist air vapor from under the roof space. Therefore, bars with a cross section of 50x50 mm are laid along the rafters. This is the counter-lattice, and the space between the waterproofing and the solid flooring is the ventilation gap.

The process of assembling an insulated roof structure consists of the following steps.

From inside the future attic, insulation is laid between the rafters. The main installation requirement is to tightly press the heat-insulating material to the planes of the rafter legs so that cold bridges do not form.
The insulation is placed in the space between the rafter joists so that there are not even minimal gaps left
A vapor barrier film is laid on top of the insulation, which is attached to the rafters with metal staples using a stapler. The film is laid in rows with an overlap of 10–12 cm. The joint must be covered with self-adhesive tape.
The vapor barrier film is laid with an overlap and secured with staples
Next, the work is transferred to the outer part of the rafter system, where a waterproofing membrane is laid over the legs in the same way as the vapor barrier below. Laying should begin from the bottom of the cornice.
Counter-lattice elements are installed and fastened along the rafters, for which wood screws 70 mm long are used. The fastening pitch is 40–60 cm.
To create a ventilation gap, bars are attached along the rafters, onto which horizontal sheathing is laid.
Lathing elements - boards - are installed across the counter-lattice. They are attached with self-tapping screws 50 cm long.
Plywood sheets or OSB boards are installed and fastened on top of the sheathing in a checkerboard pattern. The fastener pitch is 20–30 cm.

Typically, this design is used if there is no sparse sheathing on the roof, or it is assembled from boards 20–25 mm thick. Such a gap will not be sufficient for effective removal of moist air.

Video: rules for laying continuous sheathing on the roof

Continuous sheathing under soft roofing material is the only way to guarantee the quality of the final result. Minimum gaps will not reduce it, but fulfilling the basic requirement - the formation of a flat and durable surface - will create conditions under which the soft roof will last its warranty period.