Installation of lathing for soft roofing

Soft roofing, represented mainly by flexible bituminous shingles and roll materials, has gained immense popularity due to its excellent aesthetic qualities, durability, and relatively simple installation. However, the key factor determining the service life, tightness, and impeccable appearance of such a roof is not so much the finishing coating itself, but the quality and correctness of the installation of its base – the sheathing. The sheathing for a soft roof is a specially prepared surface onto which the underlayment and shingles of flexible tiles are directly laid. Unlike rigid roofing materials that can mitigate minor base irregularities, soft roofing requires an exceptionally even, continuous, and solid base.

Mistakes made during the sheathing installation stage are almost impossible to correct after the finishing coating is laid. They will inevitably manifest as waviness in the pattern, loose fitting of shingles, creases, and in the worst case – leaks and destruction of the deck due to water pooling or sagging. Thus, the sheathing is not just an auxiliary structure, but the foundation of the entire roofing system, on which its performance characteristics directly depend. The purpose of this article is to examine all aspects of constructing this foundation in maximum detail and in a structured manner: from material selection and calculations to step-by-step installation technology and quality control.

This guide covers both classic wooden sheathing and alternative options, examining the specifics of working with different types of soft roofs and architectural roof forms. Understanding the principles outlined below will allow both professional builders and competent homeowners to avoid common mistakes and ensure the roof’s reliability for decades to come. We will begin by examining the main functions and requirements for the sheathing, after which we will analyze each stage of its creation in detail.

Chapter 1: Functions, Types, and Basic Requirements for Sheathing

1.1. Functional Purpose of Sheathing in the Roofing Pie

Sheathing for a soft roof performs a number of critical functions without which the correct functioning of the entire roofing system is impossible. The primary and most obvious function is to create a plane for attaching the finishing coating. Flexible shingles and roll materials are mechanically fastened (with nails or screws) precisely to the sheathing, which ensures their reliable fixation against wind loads. The second, no less important function is forming an absolutely even, rigid, and unyielding surface. The slightest sag, bulge, or height difference on the base will be visually noticeable under the thin and pliable material, disrupting the perfect geometry of the pattern.

The third function is to provide a ventilation gap between the solid deck and the insulation layer, which is usually located below. Although the sheathing itself is solid, in combination with the counter-batten it creates the necessary channel for air movement from the eaves to the ridge. This prevents condensation from accumulating on the inner surface of the base and the insulation from getting wet. The fourth function is the even distribution of loads from snow, water, and the weight of people (during maintenance) onto the rafter system. The solid deck acts as a single slab, transferring point loads to a larger number of rafters.

The fifth function is relevant for complex roofs: the sheathing serves as a base for marking and aligning rows of flexible shingles, especially in valleys, hips, and junctions. A properly prepared base allows for precise and quick installation of the finishing coating, observing all technological offsets. Thus, the sheathing is a multifunctional structural element, on the quality of which the waterproofing, durability, energy efficiency, and appearance of the roof depend.

1.2. Main Types of Sheathing: Single-Layer and Two-Layer Systems

In the practice of installing soft roofs, two fundamentally different sheathing schemes are used: single-layer and two-layer. The choice between them is determined by the design of the roofing pie, the type of insulation used, and ventilation requirements. Single-layer sheathing implies laying a solid covering directly onto the rafter legs. This method is used quite rarely, mainly for cold (uninsulated) attics or utility buildings. In this case, ventilation of the under-roof space through dormer windows, ridge, and eaves vents must be provided.

The main disadvantage of a single-layer system is the lack of a ventilation gap directly under the deck, which can lead to moisture condensation on its inner side during temperature fluctuations. Two-layer sheathing is the classic and most correct system for insulated roofs (mansards). It consists of two tiers: the first – counter-batten, and the second – the actual solid sheathing. Counter-batten consists of battens nailed along the rafters over the waterproofing film or membrane. Their main task is to create that very ventilation gap for removing moisture vapor from the insulation.

A solid deck is mounted on top of the counter-batten battens, which serves as the base for the soft roof. It is precisely this two-layer system that is recommended by all leading manufacturers of flexible shingles, such as Shinglas, Tegola, Katepal, Icopal. It ensures maximum durability of all elements of the roofing pie. Variations within the two-layer system are also possible: sometimes, for additional leveling of the plane or with a large rafter spacing, a layer of sheet materials is first mounted on top of the spaced board sheathing, and then the final solid layer. This is already a three-layer system, used for particularly critical projects or when using uneven lumber.

1.3. Key Requirements: Evenness, Continuity, and Strength

Three mandatory requirements are imposed on the sheathing for a soft roof: evenness, continuity, and strength. The evenness of the surface is an absolute priority. Permissible deviations in the plane usually should not exceed 2-3 mm over a length of 2 meters (checked with a straightedge or a level rod). The deck should not have dips, bulges, steps between the edges of sheets or boards. This requirement is due to the fact that flexible shingles, heating up in the sun, pliably follow all the curves of the base. Water will accumulate in depressions, and the material will wear out faster on protrusions.

The continuity of the deck is the second inviolable rule. The base must be continuous over the entire area of the slopes, including the areas of eaves and gable overhangs. There should be no gaps, cracks, or omissions. This is related to two factors: firstly, fine fractions of stone granules from the back of the shingles can get stuck in the gaps, disrupting adhesion; secondly, during strong wind and rain, water under pressure can penetrate through micro-cracks. The only exceptions are technological gaps between sheet materials (OSB, plywood), left to compensate for thermal expansion.

The strength requirement implies that the base should not sag under the weight of a person (about 100 kg) during installation and repair work. The design load on the sheathing includes the weight of the roof itself, snow and wind loads for a specific region. Usually, the thickness of the sheet material or the installation spacing of the boards is standardized for a given distance between the rafters. For example, with a rafter spacing of 600 mm, the minimum thickness of plywood should be 9 mm, and with a spacing of 1200 mm – already 18 mm. Compliance with this requirement guarantees that the deck will not sag or deform over time.

Chapter 2: Selection and Preparation of Materials

2.1. Wood for Sheathing: Species, Moisture Content, Assortment

Wood remains the most common material for sheathing, especially in private housing construction. For both counter-batten and solid decking, coniferous species are predominantly used: pine, spruce, larch. Larch, which has high resistance to decay, is preferable, but its cost is significantly higher. Pine and spruce are more affordable but require mandatory antiseptic treatment. The wood must be healthy, without signs of blue stain, mold, a large number of fallen knots, or through cracks.

A key parameter is moisture content. The recommended moisture content of lumber for sheathing should not exceed 18-20%. Using wet wood (with a moisture content above 25%) is unacceptable, as during natural drying in the attic, boards and battens will warp, bend like a “propeller,” or shrink with the formation of wide gaps. This will lead to deformation of the already laid roof covering and disruption of its tightness. The lumber must be calibrated, meaning it has the same thickness and width along its entire length, which significantly simplifies the creation of a level plane.

For counter-batten, battens with a cross-section of 30×50 mm or 40×50 mm are usually used. Sometimes, a standard 25×150 mm board is ripped lengthwise for this purpose, obtaining 25×50 mm battens. For solid decking made of boards, edged or tongue-and-groove boards are used. The recommended thickness is 22-25 mm, width is 100-150 mm. Tongue-and-groove boards are preferable as they allow for a more monolithic base without through gaps. All wooden elements must be treated with fire-bioprotective compounds (fire retardants and antiseptics) before installation. Treatment is best done after cutting but before installation to protect the ends.

2.2. Sheet Materials: Plywood, OSB, CSP, SML

Using sheet materials for solid decking has several advantages over boards: they provide a perfectly even surface, are mounted faster, and create a stiffer and more monolithic base. Roofing plywood (FSF – plywood with increased moisture resistance) is considered one of the best options. The resins used for its gluing ensure dimensional stability and high resistance to moisture. The minimum recommended thickness is 9-12 mm depending on the rafter spacing. Disadvantage – higher cost compared to OSB.

Oriented Strand Board (OSB-3 or OSB-4 – moisture-resistant grades) is the most popular and economical material. OSB-3 is optimal for roofing work. The boards have stable geometry, are easy to cut and install. It is important to ensure that the board ends after cutting are free of chips and tears. As with plywood, a compensation gap of 2-3 mm must be left between OSB sheets to prevent bulging when the boards expand due to moisture and heat. Cement-Bonded Particle Board (CSP) and Glass-Magnesium Sheets (SML) belong to non-combustible materials and provide an absolutely even and strong base. However, they are heavy, difficult to cut (especially CSP, which generates a lot of dust), and require a special approach to fastening.

2.3. Comparative Analysis of Materials for Decking

For clarity, let’s present the key characteristics of the main materials for solid sheathing in a comparative table. This analysis will help make an informed choice depending on the budget, project requirements, and material availability.

Comparative table of materials for solid sheathing deck

2.4. Fasteners: Nails, Screws, Ring-Shank Nails

The reliability of the sheathing fastening is no less important than the quality of the main material. For installing counter-batten (battens to rafters), galvanized nails 70-90 mm long or wood screws 50-70 mm long are used. Nails provide faster fastening, while screws offer better pull-out resistance, which is relevant in regions with strong winds. For attaching solid deck boards to the counter-batten, nails with a length of at least two board thicknesses (e.g., 50-60 mm for a 25 mm board) are traditionally used. Nails are driven closer to the edges of the board, trying to avoid splitting.

When installing sheet materials (plywood, OSB), special roofing screws with a washer and a sharp tip, or ring-shank (screw) nails are used. The key requirement is that the fasteners must be galvanized or have another anti-corrosion coating (yellow-passivated). Rusting fasteners will deteriorate over time and leave streaks on the finishing coating. Screws and nails are driven/screwed in with a setback from the edge of the sheet of at least 10-15 mm to avoid causing chips. The fastening spacing along the perimeter of the sheet is 100-150 mm, in the middle of the sheet (at the points of intersection with the counter-batten battens) – 200-300 mm.

It is strictly forbidden to use ordinary black drywall screws for fastening sheet materials – they have no corrosion protection and are not strong enough in shear. Also, fastening sheets only at the corners or with large gaps is unacceptable – this will lead to their vibration, rattling, and possible detachment during hurricane winds. Properly selected and installed fasteners guarantee that the base will work as a single shield throughout the entire service life of the roof.

Chapter 3: Calculation and Design of Sheathing

3.1. Accounting for Loads: Snow, Wind, and Operational

The design of the sheathing begins with determining the loads that the roof will experience. These loads are summed up and transferred through the sheathing to the rafters, and then to the load-bearing walls of the building. Snow load is the main temporary load for most regions of Russia. It is calculated by the formula S = Sg * µ, where Sg is the weight of snow cover per 1 m² of horizontal surface (taken from the maps of SP 20.13330.2016), and µ is the coefficient of transition from the weight of snow on the ground to the snow load on the coating (depends on the slope angle). For a soft roof with a slope from 12° to 30°, this coefficient ranges from 1.0 to 0. For flat roofs, the snow load is maximum.

Wind load is significant for high-rise buildings and open areas. It can create both pressure on the windward slope and uplift (tearing off) on the leeward side. The sheathing, especially at the edges (eaves, ridge, gables), must be securely fastened to withstand these forces. The operational load is assumed to be 70-100 kgf/m² (or 1 kPa) – this corresponds to the weight of a person with tools who may move on the roof to maintain chimneys, antennas, or clear snow. This load is point-based and checks the local strength of the deck.

The total design load is used to check the load-bearing capacity of the rafters but also affects the requirements for the sheathing. The larger the rafter spacing, the thicker and stronger the deck must be to transfer the load without sagging. Manufacturers of sheet materials usually provide tables with recommended thicknesses depending on the rafter spacing and design snow load. For example, for OSB-3 with a rafter spacing of 600 mm and moderate snow load, a thickness of 9-12 mm is sufficient, while with a spacing of 1200 mm, 18-21 mm is already required.

3.2. Determining Counter-Batten Spacing and Deck Thickness

The counter-batten spacing is always equal to the rafter spacing, as the battens are nailed directly along them. The cross-section of the batten is selected based on the required height of the ventilation gap. The standard height is 40-50 mm. This value is considered sufficient for effective air draft from the eaves to the ridge in most cases. If the under-roof waterproofing is made of a super-diffusion membrane laid directly on the insulation, the counter-batten only serves to create a vent gap and can have a height from 30 mm.

The thickness of the solid deck is a critically important parameter. For boards, the minimum thickness is 22-25 mm. When using thinner boards (20 mm), they must be mounted more frequently, and the rafter spacing must be reduced. For sheet materials, the thickness is strictly regulated by the roofing manufacturer and depends on the rafter spacing. Let’s provide a summary table of recommendations that are general but always require verification against the technical documentation of a specific roofing brand and sheet material.

Recommended thickness of sheet deck depending on rafter spacing

It is important to understand that these values are minimum. On complex roofs, in areas with high snow load, or when using heavy types of shingles (e.g., with copper coating), an increase in thickness of 10-20% may be required. It is always better to make the base with a small margin of safety, as its replacement in the future will be comparable in cost to a complete roof overhaul.

3.3. Features for Roofs of Complex Shape (Valleys, Ridge, Junctions)

On roofs of complex shape (hip, multiple gable, with dormer windows), the installation of sheathing has its own specifics. In valleys (internal corners), the base must be especially strong and continuous, as two water catchment flows converge here. Often, an additional layer of galvanized steel, plywood, or OSB with a width of at least 500 mm on each side of the valley axis is laid over the main sheathing in the valley. This creates a rigid gutter resistant to possible leaks. Sometimes, a solid deck of boards laid along the axis of the angle is used for the valley.

In the ridge area, the solid sheathing is made with a gap. On each side of the ridge axis, the sheets or boards should not meet tightly. A ventilation gap 50-80 mm wide must be left along the entire length of the ridge for free air exit from the under-roof space. This gap will later be covered with a ridge vent element or a special flexible shingle covering. On hips (external corners, ridges), the sheathing joins at an angle, and its edges must be planed or cut so that the finishing coating lies flat, without gaps and voids.

In places where the roof adjoins vertical walls, chimneys, parapets, dormer windows, the sheathing must also be continuous and even. Often, additional battens or boards are mounted around the perimeter of such elements for reinforcement, which serve as the base for attaching flashings and junction strips. When ventilation pipes or antenna outputs pass through the roof, a hole is cut out in the deck, the edges of which must be reinforced and treated. Proper preparation of the sheathing in complex units is the key to ensuring that all subsequent waterproofing work will be performed qualitatively and leaks in these critical points will not occur.

Chapter 4: Step-by-Step Installation Technology

4.1. Preparatory Work: Checking Rafters, Laying Waterproofing

Sheathing installation cannot begin without thorough checking and preparation of the rafter system. First, it is necessary to ensure that all rafter legs lie in the same plane. For this, strings are stretched along the diagonals of the slope and along the ridge and eaves. Protruding parts of the rafters are planed off, and wooden wedges are placed in the sags or leveling strips are nailed. This operation is critically important: if the rafters are “tilted,” a level sheathing cannot be made. The rafter spacing is also checked – it should be approximately the same, permissible deviation is ± 10-15 mm.

The next stage is the installation of the under-roof waterproofing film or membrane. It is rolled out horizontally, starting from the lower edge of the eaves, with a sag of 10-20 mm between the rafters (for draining possible condensation). Subsequent sheets are laid with an overlap of 100-150 mm, the upper sheet always overlaps the lower one. It is recommended to tape the joints with connecting tape. The film is fastened to the rafters using a construction stapler or galvanized nails with wide heads. It is important not to over-tighten the film; it should lie freely.

After laying the waterproofing, a drip edge (eaves strip) is installed along the bottom of the rafters, on the eaves overhang. This is a metal strip in the shape of an angle that drains condensation from the waterproofing into the gutter and protects the fascia board and rafter ends. The drip edge is fastened over the waterproofing film with galvanized roofing nails spaced 150-200 mm apart. In the valley area, a valley underlayment – a special underlayment material of increased strength serving as an additional waterproofing layer – is installed over the waterproofing. After these preparatory works, the installation of the counter-batten can begin.

4.2. Installation of Counter-Batten and Solid Deck from Boards

Installation of the counter-batten begins with fastening battens over the waterproofing along each rafter leg. Battens with a cross-section of 30×50 or 40×50 mm are used. It is important that the battens are straight, without twist. Fastening is done with galvanized nails 70-90 mm long or screws 50-70 mm long, using 2 fasteners per intersection with the rafter. If the length of the batten is insufficient for the entire slope length, they should be staggered, on different rafters, to avoid creating a line of weakness.

After installing the counter-batten, they proceed to laying the boards. Work starts from the bottom, from the eaves overhang. The first board should be 10-20 mm thicker than the others (or a strip should be placed under it) to compensate for the thickness of the drip edge and eaves strip, which will be installed later. Boards are nailed to each counter-batten batten with two nails near each edge. Tongue-and-groove boards are joined with a lock, ordinary edged boards are laid tightly together. Boards can only be joined lengthwise on the counter-batten battens; the ends must fit tightly together.

When laying, the plane must be constantly monitored by stretching strings across the slope. All protruding knots must be cut off and smoothed. If a board has a slight hump, it is laid with the convexity upwards; during subsequent fastening, it will press against the battens. If the arc is directed downward, the board is either replaced or a wedge is placed under the sag. In the ridge area, boards from both sides should not meet, leaving a ventilation gap. After completing the deck, the surface is desirable to be sanded with coarse sandpaper attached to a sander or a block to remove small tears and burrs that could damage the underlayment.

4.3. Installation of Solid Deck from Sheet Materials (OSB, Plywood)

Installation from sheet materials is more technological and faster. Sheets also start laying from the lower corner of the slope. It is very important to orient the boards correctly. OSB and plywood boards have different strength along and across. The long side of the sheet (usually 2500 mm) should be directed perpendicular to the rafters, and the short side joints should be staggered, like brickwork. This ensures even load distribution and stiffness. A compensation gap of 2-3 mm must be left between the sheets to prevent bulging during expansion.

Fastening the sheets starts from one corner, aligning them exactly with the eaves overhang. The first row of sheets is mounted so that their ends fall exactly on the middle of the counter-batten batten. Each sheet is fastened with screws or ring-shank nails: around the perimeter with a spacing of 100-150 mm, in the middle (at the intersections with the battens) with a spacing of 200-300 mm. The setback from the edge of the sheet should be at least 10 mm. Screws are screwed in flush, not sinking the head deep into the material, but not leaving it protruding. It is important to ensure that the sheet joints fall precisely on the counter-batten battens and are not hanging in the air.

When laying the second and subsequent rows, the offset of the joints (staggering) must be at least 400-500 mm. That is, the middle of the sheet of the upper row should fall on the joint of two sheets of the lower row. This rule is mandatory. In the ridge area, the sheets are cut so that a ventilation gap remains. In valleys and on hips, the sheets are carefully cut to fit, ensuring a tight fit. After installing the entire surface, it is necessary to check it for sagging, walk on it and make sure there are no creaks or deflections. All screw or nail heads must be countersunk.

4.4. Arrangement of Eaves and Gable Overhangs

Eaves and gable overhangs require special attention, as they are most exposed to moisture from rain and melting snow. Reinforcement is done along the edge of the sheathing on the eaves overhangs. Most often, doubled or tripled boards are used for this, or sheet material laid in two layers. This is done to support the weight of the gutter system, icicles, and to provide greater stiffness to the edge where people will walk during installation.

A fascia (wind) board is mounted on the finished and reinforced sheathing of the eaves overhang. It is installed on the ends of the sheathing and rafters, carefully leveled. The fascia board serves as the base for attaching drip edges, eaves strips, and gutter system elements. It must be made of dry wood, treated with an antiseptic, and painted or otherwise protected, as it is outdoors. On gable overhangs, the sheathing also protrudes beyond the plane of the wall, forming an overhang. The edges of the sheathing on the gable are sheathed with a trim (wind) board, which protects the ends of the deck and gives the roof a finished look.

After installing the fascia and trim boards, a starter (eaves) metal strip is fastened along the eaves, over the sheathing and over the drip edge. It is designed to protect the edge of the sheathing from moisture and serves as a guide for the first row of flexible shingles. On the gables, end (gable) strips are installed, which perform a similar protective function and cover the ends of the sheathing. All strips are fastened with roofing nails spaced 100-150 mm apart in a staggered pattern. Proper arrangement of overhangs is the finishing touch in preparing the base, after which the underlayment can be laid.

Chapter 5: Quality Control and Common Mistakes

5.1. Methods for Controlling Evenness, Continuity, and Strength

Quality control of the sheathing installation should be carried out at every stage. After installing the counter-batten, it is checked that all battens are securely fastened, do not “play,” and lie in the same plane. To check the plane, several strings are stretched along the diagonals of the slope and across. The gap between the string and the surface of the battens should not exceed 3-5 mm. After installing the solid deck, a more thorough check is carried out.

The main control tool is a straightedge (a straight rod or aluminum rule 2-3 meters long). It is applied to the deck in different directions: lengthwise, crosswise, and diagonally. The permissible gap between the straightedge and the surface is no more than 2-3 mm. Special attention is paid to the joints of sheets or boards: there should be no height differences (“steps”). A visual check for continuity is performed: there should be no gaps when viewed against the light. The “sliding” method can be used: run a gloved hand over the surface – it should not catch on knots, splinters, or protruding nail heads.

Strength is checked by simply pressing with a foot on various areas of the deck, especially in the center of the spans between supports. The base should not sag, creak, or spring. If a board of small thickness or sheets violating thickness recommendations are used, sagging will be felt immediately. The reliability of fastening is also checked: try to pry the edge of a board or sheet – it should be firmly fixed. Quality control is not a formality but a necessary procedure that will prevent huge problems in the future. It is better to spend time correcting defects at this stage than to deal with the consequences after laying expensive finishing coating.

5.2. Common Mistakes and Their Consequences

Experienced roofers know the typical mistakes made by inexperienced installers or homeowners trying to save money. The first and most common mistake is using wet lumber. The consequences appear after six months to a year: the boards dry out, wide gaps of 5-10 mm appear between them, the deck “plays,” nails partially come out. The flexible shingle repeats this deformation, water and snow can leak into the gaps, adhesion is disrupted.

The second mistake is saving on material thickness or increasing the counter-batten spacing. Using OSB 9 mm thick with a rafter spacing of 900 mm will lead to guaranteed sagging of the deck under snow or a person’s weight. This will cause water pooling in the sags, destruction of the granules, and the bitumen layer itself. The third mistake is non-compliance with the rule of staggering joints when installing sheet materials. If the joints of several sheets fall on one line, it creates a “weakness axis” along which deformation or even rupture can occur.

The fourth gross mistake is the absence of a ventilation gap at the ridge or its blocking. This completely violates the principle of under-roof space ventilation. Moisture will accumulate, leading to wetting of the insulation, rotting of the sheathing and rafters, and mold appearance. The fifth mistake is poor fastening. Too rare spacing of nails/screws, using short or non-corrosion-resistant fasteners. In strong winds, such a deck may start to “walk,” detaching from the counter-batten battens, which will create a rumble and can lead to damage to the roofing.

5.3. Ventilation and Wood Protection Issues

Even a perfectly installed sheathing will not last long if proper ventilation of the under-roof space is not ensured and the wood is not protected. Ventilation is carried out by air intake through eaves vents (soffits) and exit through ridge or spot aerators. The height of the vent channel created by the counter-batten (40-50 mm) must be constant over the entire slope plane. No communications or insulation should block it.

To protect the wood, treatment with deep-penetration antiseptic compounds is mandatory. All wooden elements must be treated: rafters, counter-batten, deck boards, fascia and trim boards. The ends should be treated especially carefully. It is better to treat after cutting but before installation so that the composition gets on all fresh cuts. For elements outdoors (fascia boards), in addition to antiseptic, it is recommended to use semi-transparent or opaque paints that additionally protect against UV radiation and precipitation.

In regions with high humidity or for critical projects, the use of wood subjected to autoclave impregnation under pressure (impregnated) can be considered. Such wood has a greenish or brownish tint and has increased resistance to fungus, mold, and insects. Another modern method is heat treatment of wood, which changes its structure, making it insensitive to moisture and biological damage. These materials are more expensive, but their durability justifies the investment.

Chapter 6: Special Cases and Alternative Solutions

6.1. Sheathing Over Old Roof Coverings and for Reconstruction

Often during reconstruction, the question arises: is it possible to lay a soft roof over an old covering, for example, slate or metal tiles? The answer is yes, but only under strict conditions. The old covering must be strong, without signs of rot or corrosion of the load-bearing elements. The surface must be thoroughly cleaned of moss, dirt, and peeling paint. The most important thing is to create a level, continuous, and ventilated base over the old covering.

For this, wooden beams (analogous to counter-batten) with a thickness of at least 40 mm are mounted over the old roof to create a vent gap. The beams are fastened to the old sheathing or rafters with long screws, having first found the load-bearing elements. Then, a solid base made of OSB or plywood sheets is laid over these beams. This method avoids the laborious and messy process of dismantling the old roof but increases the load on the rafter system. A calculation of the load-bearing capacity of the rafters to withstand double the weight is mandatory.

During the reconstruction of flat or low-slope roofs with a concrete base for soft roll roofing (e.g., built-up), a different approach is used. Here, sheathing as such is not needed. Instead, a screed made of cement-sand mortar or asphalt concrete is made to create slopes towards the drains, and then the base is primed with bitumen primer. However, if it is necessary to raise the level or lay insulation, wooden joists or metal zigzag purlins are constructed, over which a solid deck made of flat slate, CSP, or plywood is then mounted.

6.2. Use of Ready-Made Systems and Plastic Sheathing

The modern market offers innovative solutions to speed up and improve installation. These include ready-made systems of ventilated sheathing. Often these are kits of plastic adjustable supports (stands) that are fastened to the rafters, and special boards (e.g., made of pressed wood wool with bitumen impregnation) that are inserted into these supports. Such a system guarantees a perfect plane, excellent ventilation, and quick installation. However, its cost is significantly higher than traditional wooden ones.

There are also plastic strips and battens positioned as an eternal alternative to wooden counter-batten. They do not rot, do not warp, and have stable dimensions. Their use is especially relevant in aggressive environments (e.g., by the sea) or when using materials with high residual moisture (e.g., concrete slabs) in the roofing pie. Another solution is metal sheathing made of galvanized profiles similar to those used for drywall. It is used in frame construction or on roofs of complex shape where high precision and non-combustibility of the structure are required.

The choice of such systems is justified for large commercial projects where installation speed and guaranteed quality are critical. In private housing construction, they are still rarely used due to the high price and the need to involve specialists familiar with a specific system. However, these technologies represent the future, as they minimize the human factor and increase the durability of the structure.

6.3. Features for Rolled Built-Up Materials

Although the article’s topic is focused on sheathing for flexible shingles, it is worth briefly mentioning the features for rolled built-up materials (euro roofing felt, glass insulation, etc.), which also belong to soft roofs. For them, the base must be not only even and continuous but also capable of withstanding high temperatures (up to 200-250°C) from the torch during application. Wooden bases in this case are risky due to the danger of fire.

Therefore, for built-up roofs over wooden rafters, a classic two-layer sheathing is first made, and then, as a separating and fireproof layer, flat slate (asbestos-cement sheets) 8-10 mm thick, CSP, or SML is laid over the solid wooden deck. These sheets are fastened to the wooden deck with screws. The built-up application is performed on this non-combustible base. On concrete bases (slabs, screeds), priming with primer is performed and the material is applied directly to the concrete. Thus, the requirements for the base under a built-up roof are even stricter, including the mandatory criterion of fire resistance.

Conclusion

The installation of sheathing for a soft roof is a comprehensive technological process where there are no minor details. The thoroughness of material selection, the accuracy of calculations, and the scrupulousness in installation determine whether the roof becomes a reliable protection for the house for 30-50 years or a source of constant problems and costs. The key principles are creating a level, continuous, strong, and ventilated base. A two-layer system with counter-batten and a solid deck made of high-quality dry wood or moisture-resistant sheet materials is the gold standard.

You cannot save on deck thickness, fastener quality, or antiseptic treatment. Special attention should be paid to the units: valleys, ridges, eaves, and junctions. Modern alternative systems (plastic, adjustable) offer new possibilities, but the classic one, done by the rules, will never let you down. Remember that the sheathing is hidden under the finishing coating, and correcting its defects after the work is completed is extremely difficult and expensive. Investing time, money, and attention at this stage is the most reasonable and reliable insurance for the entire roofing system of your house.