Soft roofing is increasingly used to design roofs in low-rise construction. It is practical, beautiful, modern and reliable. But the longevity of its service will depend on whether the installation was carried out correctly. The correct sheathing underneath is of considerable importance. soft roof. How to make it correctly, what requirements should it meet?
Also known as asphalt shingles. It was first introduced to the building materials market about 30 years ago. This elastic material is made from fiberglass or polyester, which are impregnated with bitumen compounds. The result is a water-resistant, durable yet flexible material that is ideal for finishing roofs.
Surface flexible tiles always covered with a special coating - fine crumbs obtained during the processing of various minerals. And the bottom layer has an adhesive base that allows you to glue the tiles to the roof. This type of tile is used when arranging roofs with slope angles of at least 11-12 degrees.
Note! Flexible tiles are distinguished by a wide selection of shades, colors, and sizes. This is why you should not purchase materials made by different manufacturers, even if they are very similar to each other.
Due to their softness, such tiles require a special base. It can only be laid on a crate made in a certain way.
Prices for various types and manufacturers of flexible tiles
What is lathing, its types
Lathing is an element necessary for every roof, which is a system of boards and beams on which it is attached. roofing material. It happens different types, the choice among which is made depending on what roofing material is used. For example, if the roof is covered with slate, then the sheathing may be sparse, that is, there will be gaps between its elements (a certain pitch). If soft coverings are to be installed on the roof, then the sheathing should be continuous, without gaps. To lay bitumen shingles, you will have to use a continuous type of sheathing.
Note! The lathing can have two layers at once - sparse and continuous. Due to this, it will be possible to achieve good ventilation of the roof, install thermal insulation and improve the quality and reliability of the roof as a whole.
The sparse lathing is always laid perpendicular to the roof rafters (parallel to the ridge), the solid one is fixed on top of the mounted sparse one. At the same time, do not forget about laying heat and waterproofing materials.
High-quality and correctly installed sheathing for a soft roof must meet the following criteria:
- be durable;
- do not bend under the weight of the roofing material;
- remain resilient even under the influence of environmental factors;
- be level - have no bumps, protrusions, or irregularities, all sharp elements are removed from it, the heads of nails and screws should not protrude above the level horizontal surface boards;
- should not have large gaps between individual elements (maximum step - 1 cm).
Note! Sometimes solid lathing is laid directly on the rafters, without using sparse lathing - the so-called single-layer flooring. This is done to speed up the construction process; usually the option is used only for houses that do not need enhanced insulation and waterproofing.
Materials for making lathing
Sheathing for soft tiles can be made from several types of materials. The main requirements for them are strength, reliability, durability and evenness.
Plywood most often used to create sheathing for soft tiles. This is an environmentally friendly material, multi-layered, quite wear-resistant, inexpensive, easy to use and durable. The main thing is to purchase a moisture-resistant option for the roof - ordinary plywood cannot be used here. The most suitable brand is FSF plywood. It has the qualities necessary for creating sheathing - fracture strength, ductility, low density, light weight, and is not afraid of fungus. This plywood is resistant to moisture, which means it will not rot. In the process of its production, residues from the processing of coniferous wood are used.
Another good and suitable material for creating sheathing is OSB board, a slightly improved version of the chipboard familiar to many. She's different high level moisture resistance, dense and durable, not afraid of snow loads, very smooth and does not deform under the influence of moisture. It will ensure that there are no differences in height and will make the sheathing perfectly level. The material is quite simple to install and does not require the use of any special tools.
The sheathing for a soft roof can be made from edged or tongue-and-groove pine boards. The material should have low humidity - no more than 20%. The width of the boards used should be 140 mm. Main disadvantage– the tendency of boards to deform; due to moisture, they often warp and bulges and cracks form on the surface of the sheathing.
Important! Before using wood in construction, it must be treated with antiseptic compounds, as well as drugs that increase the fire resistance of the material.
Prices for various types of construction boards
Construction boards
Rules for making lathing
The creation of lathing can only be done in compliance with certain rules. Otherwise, the structure will not last long and will quickly deteriorate. And the manufacturer of soft tiles does not provide a guarantee for its material in case of violation of the installation technology.
So, special attention requires determining the angle of inclination of the roof slope. If it is very small and is only 5-10 degrees, then soft tiles need to be laid only on a solid sheathing made of plywood and boards. And in general, in this case, this material is not recommended. If the slope angle is within 10-15 degrees, then the sheathing is made of timber with a section of 45x50 mm, covered with plywood or OSB. The bars are installed in increments of 45 cm. If the angle exceeds 15 degrees, then a beam of the same cross-section is used to create the sheathing, but mounted in increments of 60 cm.
Attention! When calculating the requirements for sheathing, it is important to take into account the climatic characteristics of the region - the load that the roof will experience due to snow cover. The load that will be created by the roofing material itself is also taken into account.
Table. The dependence of the pitch of the rafters on the thickness of the material used.
| Step, cm | Plywood thickness, mm | OSB thickness, mm | Board thickness, mm |
|---|---|---|---|
| 30 | 9 | 9 | Not used |
| 60 | 12 | 12 | 20 |
| 90 | 18 | 18 | 23 |
| 120 | 21 | 21 | 30 |
| 150 | 27 | 27 | 37 |
When installing the sheathing, it is worth remembering about the compensation gaps that are left between the elements of the material from which the solid base is created. The gap between sheets of plywood or OSB should be 5-10 mm. If the material swells, it will save the roof from curvature, and the roofing material from damage.
Plywood prices
Lathing technology. Design Features
The basis of any roof is the rafter system. They are fixed on the Mauerlat - a support that is mounted around the perimeter of the house and will experience maximum load. Therefore, the Mauerlat must be durable and securely fixed. Fixation is done using anchor bolts. If the walls of the house are not built of wood, but of aerated concrete or brick, then it is recommended to additionally fix the anchors with cement.
After installing the Mauerlat, the creation occurs rafter system. Rafters can be made of wood, metal and other materials. Wood is the easiest to work with; it can be easily adjusted to certain dimensions on site, and you don’t have to order special equipment to lift it up. The rafters are installed in increments, which are determined based on the thickness and width of the materials used for the continuous sheathing (if it will be laid immediately on them). For example, with a board thickness of 2 cm, the step can be 50 cm. The same step can be used when laying plywood or OSB with a thickness of 10 cm. If the step is too large, the base of the roof will bend over time under the weight of the roofing material itself.
Note! If the sheathing is mounted from a board, then it is important to round its edges in order to avoid the occurrence of unevenness on the surface in the future.
Do not forget that the roof must have ventilation. The gap that is formed between the solid and sparse sheathing is quite suitable as it. If the boards are laid on joists, then it is important to think about how to make vents. Otherwise, condensation will accumulate under the roofing material, which will cause negative impact for all elements included in the roof structure.
Waterproofing too important aspect which should not be neglected. Material capable of retaining moisture is laid on the rafters and fixed with bars - a counter-lattice (sparse lathing) is formed.
Thermal insulation is useful if the house is planned to be used as a residence throughout the year. In the case of temporary country house where they will live only in the summer, thermal insulation may not be useful.
The sheathing materials are fastened using self-tapping screws. Nails are used less frequently. However, regardless of which fastening option is used, the caps must in any case be recessed into the base. Otherwise, the coating on top may be damaged. Fastening is done in increments of at least 15 cm.
Sheets of plywood are laid staggered - their joints in parallel rows should not be in the same place. OSB boards are installed in checkerboard pattern, that is, seam spacing is also necessary. The joints of longitudinal seams should be located on the battens of the sheathing (counter-lattice).
Important! After the work on creating the sheathing is completed, the lining carpet is laid on a flat base. Only after this the most flexible tiles are installed.
Don't forget about the drip
The protection of eaves and rafters from moisture is provided by a drip tray. Its purpose is to remove moisture from the roof into the drainage system. Thus, this element will protect the wooden parts of the structure from exposure to moisture, the onset of rotting processes, and the development of mold or mildew.
The drip line is fixed on the edge of the roof in a vertical position. Due to this, water from the roof will flow directly into the drain. As a rule, this element is made of galvanized steel, painted in a color to harmonize with the roofing material. It is installed along the entire perimeter of the roof. Fastening is done to the sheathing.
Creating sheathing for soft tiles
Step 1. Taking into account bearing capacity foundation and the shape of the roof, a rafter system is created from boards with a section of 150x50 mm. The elements are installed in increments of 60 cm.
Step 2. A vapor barrier membrane is attached to the rafters from the inside, which will prevent moisture coming from inside the house from affecting the roofing materials. The vapor barrier roll is rolled out parallel to the eaves, the material is fixed by using a construction stapler to the rafters. Individual strips of material are laid overlapping each other. The overlap is 10-15 cm. The membrane is also overlapped onto the walls.
Step 3. Insulation is being laid. The mineral wool that will be used in this case has a thickness of 20 cm. This is the best option for the regions of Russia. In general, the thickness of the insulation will vary depending on the climate of the area. The material is laid on top of the vapor barrier membrane. The width of the insulation should be equal to the installation pitch of the rafters. If the material is laid in several layers, then the vertical seams should be spaced apart.
Attention! From the inside, several support boards are nailed to the rafters through the membrane, which will help hold the insulation in place.
Step 4. A counter beam with a cross section of 5x5 cm is installed in increments of 60 cm. Another layer of thermal insulation 5 cm thick is laid between the individual beams.
Step 5. A vapor diffusion membrane is being laid, which will protect the roofing materials from dust and moisture. It is laid on the insulation, the roll of material is rolled out parallel to the cornice. The individual strips are laid with an overlap of at least 10 cm. It is also ensured that the membrane extends 20 cm beyond the contour of the insulated layer of the building. The material is fixed using a stapler. The overlaps are additionally taped with adhesive tape.
Step 6. To ensure under-roof ventilation, a ventilation chamber is created. To do this, counter beams with a section of 5x5 cm and a pitch of 30 cm are installed parallel to the rafters. The beams are fastened in a checkerboard pattern so that there is a free gap of about 5-10 cm between them every 1.5-2 m.
Step 7 A continuous base for flexible shingles is created from oriented strand board or plywood. The thickness of the material is at least 9 mm. The slabs are laid staggered relative to each other, leaving small gaps between them - 4-10 mm. The sheets are laid parallel to the cornice.
Step 8 The cornice strips are being attached. They are installed on the edge of a solid base. Fixation is carried out with self-tapping screws in increments of 25-30 cm. Individual elements are installed with an overlap on each other. The overlap must be coated with sealant.
After this, the underlay carpet is laid and the soft roof is laid directly.
Prices for OSB (oriented strand boards)
OSB (oriented strand board)
Video - Creating a base for a soft roof
The sheathing is one of the most important parts in a roofing system created using soft tiles. Creating a sheathing is not difficult, but it is important to remember all the subtleties of installation, otherwise the roofing material will not last long.
And much more. If the material is used for a wall, as in frame houses OSB boards can be insulated, and a variety of materials are suitable for this.
But in this article we will talk about how to use OSB for a soft roof. After all, this material can be an excellent basis for your roof.
OSB thickness for soft roofing
The time has come to decide on the choice of material, and the problem is that OSB is available in 4 classes and you need to choose OSB only with the required characteristics.
OSB for a soft roof should be class 3; it is this class that is waterproof and can bear physical stress.
Now, let’s determine what the thickness of OSB should be for a soft roof, everything will depend on the pitch of the rafters, and the larger it is, the thicker the sheets laid on top should be.
Here are some approximate data on the thickness of OSB for the roof:
- Step 300 - OSB thickness 9 mm.
- Step 600 - OSB thickness 12 mm.
- Step 900 - OSB thickness 18 mm.
- Step 1200 - OSB thickness 21 mm.
Also, do not forget that with increasing thickness, the weight of the OSB slab also increases, therefore, with large spans, the construction of the roof becomes much more complicated, and overweight she has no use for it. After all, this subsequently puts additional loads on the walls and foundation.
Installation of OSB under a soft roof can be carried out directly on the rafters. But for this it is necessary that their pitch be within 50-60 centimeters, and the OSB thickness be 12 mm.
Laying nuances:
- OSB is laid perpendicular to the rafters.
- The beginning and end of the OSB should end and be attached to the rafters accordingly.
- The sheets should be staggered so that the vertical seams do not fall in one line.
Don't forget that OSB is natural material and it will expand with temperature changes, so to prevent the edges from fraying and the sheets from warping, leave small gaps in the seams - from 3 to 5 millimeters.
The material must be fastened to the rafters with nails, and their length should be 50 mm in the aisles, so that the material can move freely when expanding. If the nail is short, it can simply be completely pulled out of the rafters.
It is recommended to use screw nails; this allows the fastening to be more reliable over time than with a regular nail.
It is also very important that the OSB lies parallel to the ridge and strictly perpendicular to the rafters. If you overeat by a few centimeters, the flooring will not forgive it. Your OSB end edges will be very beveled in relation to wooden frame roofs.
To prevent this from happening, pull a rope that would serve as a guide for laying the sheets and always check everything so that you don’t have to disassemble everything later.
Of course, in some cases you can correct it by trimming the sheet, but if you trim each sheet, the work will become several times more complicated.
The main difficulty with laying OSB to the rafters, this is their rise there. For such work you need one or even several assistants.
Laying OSB under a soft roof on lathing
The option described above does not use lathing, so laying OSB under a soft roof may not be of very high quality. The problem is that the long joints of the sheets are actually lying in the air, which means that on your roof these places will be vulnerable.
And the problem is not at all that these edges can be deformed by temperature changes. The fact is that when snow gets on the roof, it puts a very large load on all the material and weak points there shouldn't be. A small deflection and a hole may appear in your roof, which in a short time will render part of the roof unusable.
To avoid such sad cases, many craftsmen recommend adding an additional sheathing of 20 or 25 boards. The laying of such boards is done so that the long edges of the OSB fall on this sheathing and are attached to it. Inside, under the OSB, there should also be two more boards that do not allow the sheet to sag.
When laying OSB on the roof, pay special attention to the weather, or protecting the sheets from rain. When exposed to moisture, the sheets swell and increase their volume by 2-3 mm - even though they are moisture resistant . And if you finish the roof with dry sheets, you will have a difference in thickness. And all this significantly worsens the quality of your roof.
Since sheets of size 2440×1220 or 2500×1250 are usually used for such purposes, the distance between the spans of the sheathing will be either 55 - 60 centimeters when using one board under the middle of OSB or 35-40 when there are two boards there.
In the first case, the thickness of OSB-3 should be 12 millimeters, in the second, a 9 mm panel is enough.
The material is attached to nails, the sheet is nailed around the perimeter and in the middle in one or two rows. The distance between nails in a row should be approximately 150 mm.
We also don’t forget about the joints, where the distance should be from 3 to 5 mm. This will allow the sheets to expand freely with temperature changes. If this is not done, the sheets will begin to press on each other at the joints and, at a minimum, will crumble and become deformed.
Video - soft roofing on OSB
Soft roofing in recent years has gained popularity among developers. But not everyone knows in advance that the base on which bitumen shingles are usually laid is very different from the sheathing on which slate, ondulin or metal tiles are mounted. Let's try to figure out how the sheathing for a soft roof should be arranged and how its installation differs from the installation of conventional sheathing.
The mauerlat on which the entire rafter system rests serves as a kind of foundation for the roof. Flexible tiles do not tolerate unevenness, unnecessary bends, height differences and protruding nails in the base on which they will be laid, so it is necessary to take the geometric parameters of the roof structure very seriously from the very beginning. All mauerlat bars must lie strictly horizontally for any structure configuration. And the lines connecting the ends of the mauerlats at the ends of the buildings should make an angle of 90° with them. If a pitched roof is also provided at the ends, then the end Mauerlat should lie perpendicular to the longitudinal ones in the same horizontal plane with them.
Rafters - the frame of the future roof
If the Mauerlat is laid and secured correctly, then installation of rafters prepared according to one template, even for figured roofs, will be simple. As a matter of fact, this is where the similarity with frames for other roofing materials ends. Under rigid roofing sheets, the sheathing can be made from edged boards in one layer with an interval between boards of 150–400 mm. Under flexible tiles it is necessary to prepare a continuous, even and smooth base in two layers:- The actual sheathing is made of calibrated (one thickness) edged boards with a width of 100 mm, which can be mounted at intervals from 100 to 400 mm.
- A solid base on which soft tiles are glued, made of plywood or OSB-3 board (osb, OSB-3)
Plywood and/or OSB-3 board must be moisture resistant! All wooden structures roofs: mauerlat, rafters, ridge girder, racks, struts, boards and timber for sheathing, must have a humidity of no more than 20%.When calculating the distance between the rafter legs, it is necessary to take into account the thickness of the board, plywood sheets or OSB boards. If the pitch is 500 mm, then the thickness of the board can be 20 mm, and plywood or OSB boards can be 10 mm. With a step of 1000 mm, the thickness of the board should be 25 mm, and plywood or OSB board should be 20 mm thick. The distance may be different, and accordingly, the thickness of the boards and sheets of plywood, or OSB-3 boards should also be different. Here you need to understand that the board serves as a sheathing to support the slab or plywood. If the distance between the boards is too large, sheet material may over time bend, sag between the supports, which will lead to deformation of the soft roof. The figures for the width of the board and the thickness of the materials used are minimal. Therefore, if you have the funds, you can purchase plywood or a board of a thickness greater than that required by calculations. In this case, the pitch of the board can be slightly increased. If the thickness is less than required, it would be better to make the sheathing of boards continuous. What is the reason for this? The point is mechanical characteristics materials:
- The board can maintain its rigidity for decades when the right conditions operation and will lie flat even with a rafter pitch of 1200 mm or more. Of course, the board must have a thickness corresponding to this step.
- Over the years, plywood and OSB-3 boards can sag under the influence of temperature changes and variable humidity if they rest on points or support lines with a distance of even 500 mm between them.
- Despite all its rigidity, a board can “lead” over time, become warped, and the edges of individual boards can move out of the general plane of the surface. But flexible tiles don’t like this. It will tear, be pressed, or rub through, which will necessitate roof repairs.
- Obviously, using only boards or only plywood or OSB boards will lead to the fact that very soon the bitumen shingles will begin to tear at the seams of the boards or sag along with the boards or plywood. This may mean that the roof installation will have to be done again.
- Only the combination of the rigidity of the board and the flat surface of OSB or plywood will give reliability to the base for soft tiles, and there will be no need to repair the roof for a long time.
To find the best option, you need to find out the cost of all materials and calculate the consumption when different options step. For example, the cost of an OSB-3 board with a thickness of 20 mm is almost twice as high as the cost of this board with a thickness of 10 mm. The preparation of roof truss structures for installation must take into account the fact that wood is a flammable material and susceptible to rotting. Therefore, it is recommended to carry out appropriate treatment with fire-retardant impregnations and antiseptics, and in places where the rafter legs come into contact with the wall, it is better to lay waterproofing material. For example - roofing felt. A layer of waterproofing must be placed under the Mauerlat. 
Sheathing device
The sheathing for a soft roof must meet the following requirements:- A continuous, flat, smooth surface of the base without deflections, potholes, chips, cracks and protruding chips or nails.
- Technical gaps between OSB slabs or sheets of plywood necessary to compensate for their possible expansion should not exceed 6 mm.
- During installation, the edges of sheets and slabs must be cleaned so that they are not sharp, even if they lie close to each other.
They will serve as protection against water entering the wooden structures of the rafter system. If you plan to install gutters, then they need to be installed before the drip line. General Guide
OSB floor installation
Let's list general principles installation of floors made of OSB boards.
Slabs with straight edges should be joined on joists, maintaining an expansion gap of at least 3 mm around the slab. When installing slabs between walls or in the case of floating floors, a 12 mm gap should be left between the slab and the wall.
Lay the slabs with their main axis perpendicular to the joists. The connection between the short edges of the slab should always be on the joists.
The slab used for the roof or floor should be mount with seal facing down. If OSB boards are laid in a row longer than 12 m, an additional gap of 25 mm should be left
Layout of OSB boards on the floor
Long edges not supported by joists must have a tongue-and-groove profile, an auxiliary support, or a connecting H-bracket.
If the ceiling does not have a roof, then during precipitation, drainage holes should be made for drainage.
At wooden floor the first floor of the building, wind protection should be created on the underside of the floor structure, plus additional waterproofing directly on the ground.
Table preliminary assessment dependence of the distances between the logs and the thickness of the slab used in housing
To fasten the boards, use spiral nails 51 mm (2″) long, or from 45 mm (1 3/4″) to 75 mm. we drive in every 30 cm on intermediate supports and every 15 cm on slab joints.
In order to increase the rigidity of the floor, you can glue the slab to the joists using synthetic mounting adhesive (adhesives based on water based will not be able to provide a reliable connection due to the waxy surface of ContiFinish).
Tongue-groove joints should be glued (for example, with D3 glue).
Installation of walls made of OSB boards
Plates OSB on walls can be mounted in horizontal and vertical positions. Between slabs and around door and window openings be sure to leave a gap of min. 3 mm.
The recommended slab thickness for wall cladding is 12 mm with a distance between wall supports of 400 mm and 600 mm. For additional thermal insulation of walls, it is recommended to use mineral wool with facing in the form of mineral plaster.
To fasten wall plates, use 51 mm (2″) spiral nails or 45 mm (1 3/4″) to 75 mm ring nails. We drive nails every 30 cm on intermediate supports and every 15 cm on slab joints.
On the outer edges of the walls we drive nails every 10 cm. The distance from the nail to the edge of the slab should not be less than 1 cm.
Installation of a roof made of OSB boards
Before installing the sheathing, make sure that the rafters or sheathing form a flat surface. Curved or uneven rafter legs will affect the final appearance of the roof and make installation difficult (for example, if there is a large unevenness, it may not be possible to fit a tongue-and-groove joint along the entire length of the slab).
Boards that have been wet by rain should be left to dry completely and protected from biological corrosion before tiles, roofing sheets, thermal roofing felt or shingles are laid.
The unheated space under the floor or attic should be well ventilated. Ventilation holes must be at least 1/150 of the entire horizontal surface.
The greatest operating load should fall on the long main axis of the slab. The connection of the short edges of the slab should always be on the supports of the roof (walls or floor). Long edges should rest on auxiliary supports and have a tongue-and-groove connection or an H-bracket connection.
A gap of min. should be left between slabs with straight edges. 3 mm to give the slab the ability to change dimensions as temperature conditions change. The slab must be laid on at least two supports, and the joints of the slabs must also rest on the supports. While fastening the slab, workers must stand on the rafters or sheathing, observing safety rules.
Table of preliminary assessment of the dependence of the distances between
rafter legs or battens and thickness
used slabs for roofs with a slope of more than 14 degrees:
If the roof structure has openings for chimneys, then the roof sheathing must be moved away from the chimney at a distance in accordance with the accepted Building Regulations.
For fastening slabs OSB on the roof, nails with a length of 51 mm spiral or from 45 mm to 75 mm ring should be used. We drive nails every 30 cm on rafters or sheathings and every 15 cm on slab joints. The distance from the nail to the edge of the slab should not be less than 1 cm.
ATTENTION!! OSB boards must be used according to a design that meets the requirements of the relevant Building codes and rules. The manufacturer's recommendations given are for informational purposes only, the final decision for each case of using slabs in building structures must be accepted on the basis of qualified engineering calculations.
The term “soft roofing” combines a whole group of materials. These include roofing felt, roll fused coatings, and soft tiles. Despite the external differences, all of these materials are made on the basis of modified bitumen, which gives the final roofing products softness and flexibility. And also one important feature: they are not able to maintain a rigid shape on their own and withstand external loads.
Bituminous materials perform their function only when laid on a rigid and durable frame. When creating a soft roof, such a frame is used as a sheathing in the form of a smooth, continuous flooring.
When constructing a sparse structure, its elements (boards) are placed on the rafters not in a continuous pattern, but with a certain step. On average, this step is 20-50 cm. This design is not suitable for soft bitumen materials, as they will sag between the elements.
A soft roof requires a continuous sheathing, which is a flooring made of boards, OSB, or plywood. A small gap between elements is allowed, but it should not exceed 1 cm.
Types of continuous lathing
So, there must be a continuous flooring under the soft roof. We have decided on this. But the sheathing for a soft roof can consist of more than just this layer. There are 2 types of solid sheathing:
- Single layer flooring– the sheathing elements are laid parallel to the ridge, directly on the rafters. Boards (boards), plywood or OSB are used as elements. Single lathing is rarely used, mainly for laying roofing felt.
- Double flooring- a combination of two layers, sometimes composed of different materials. The first layer - the working one - is, in fact, a sparse sheathing. It consists of boards (beams) that are mounted at speed. Then a second, now continuous layer is laid on it - flooring made of boards, OSB or plywood. Double lathing makes it possible to form a ventilation gap under the decking and place a thermal insulation pie between the rafters. Therefore, this design is preferable for all modern bituminous materials (also for flexible tiles).
Let's consider the technologies for constructing continuous sheathing of all available types.
Installation of single-layer continuous sheathing
Single-layer sheathing is laid directly on the rafters, without any additional elements. Suitable for budget construction using roofing felt, without forming an insulation cake under the roof.
Option #1 – lathing from boards
For continuous single flooring, you can use tongue and groove boards or planks. Unedged boards are not suitable, since all their unevenness will be reflected on the surface of the soft roof. And this will negatively affect the decorative and moisture-proofing properties of the roof.
This type of lathing is the simplest and consists of boards packed across the rafters.
Requirements for boards for continuous sheathing:
- The boards should be smooth, without knots.
- Their width is 100-140 mm, thickness - 20-37 mm (depending on the pitch of the rafters: up to 900 mm - thickness 20 mm, 900 mm - 23 mm, 1200 mm - 30 mm, 1500 mm - 37 mm).
- Humidity – no more than 20%. This is due to the fact that raw wood will sooner or later begin to dry out and the fastening elements will begin to fall out of it. In addition, on a damp base, the service life of bituminous materials is reduced.
- The boards must be antiseptic to prevent putrefactive processes, the appearance of wood-boring beetles and fungal plaque.
During the installation of such sheathing, the boards are fixed on top of the rafters, perpendicular to them, along the ridge. Since the boards tend to warp, forming a concave tray on one side and a convex tray on the other, the sheathing must be laid with trays on top. Then the water that has leaked through the roofing material will fall into the tray, follow the ledge to the eaves and flow down it outside without getting into the attic.
Installation is carried out from the bottom up, starting from the overhang. The joints of the boards along the length are laid on supports (on the rafters). Nails (screws) are driven closer to the edges, while trying to recess the heads a little into the wood. Between adjacent boards (in height) a barely noticeable gap is left - about 3 mm. It serves to level out thermal deformations of wood that occur during changes in humidity and temperature. As conditions change, the sheathing boards will contract and expand, so if they are fastened too tightly, unevenness is likely to occur.
Option #2 – lathing from panel materials
Instead of boards, you can attach panel materials to the rafters - plywood or OSB. They have high moisture resistance and flexibility, necessary for long-term service on the roof.
The use of panel materials allows you to speed up the process of installing the sheathing and obtain a perfectly flat base surface for subsequent layout roll materials or bitumen shingles.
Requirements for panel materials:
- High moisture resistance. The parameters required to work in wet conditions on the roof, not all panel materials have. Among those suitable for roofing are OSB-3 (moisture-resistant brand of oriented strand boards) and FSF (moisture-resistant plywood).
- Thickness - 9-27 mm (depending on the pitch of the rafters: if this distance is up to 600 mm, then the thickness of the sheet should be at least 9 mm, if 600 mm - 12 mm, if 900 mm - 18 mm, if 1200 mm - 21 mm , if 1500 mm – 27 mm).
- The shields must be impregnated with an antiseptic to protect against fungal infections. This is necessary because OSB-3 and FSF are resistant only to short-term exposure to moisture and require coating with waterproofing materials on the roof. Therefore, additional protection should not be neglected.
Sheets of plywood or OSB are laid on the rafters with the long side parallel to the ridge. In this case, the joining seams of adjacent rows should not coincide. The sheets are mounted in a checkerboard pattern, staggered.
A gap of 2 mm is left between adjacent sheets so that when moisture accumulates, they do not swell. If installation is carried out during cold periods, the gap is increased to 3 mm to compensate for the expansion of heated sheets in summer.
The panels are fixed with fastening elements (screws or rough nails) on each rafter - in increments of 30 cm, at the junction of the ends - in increments of 15 cm, along the edges - in increments of 10 cm.
Installation of double continuous sheathing
Double sheathing is a two-tier structure, the first layer of which is boards laid in rows, the second continuous layer is flooring made of boards, OSB, or plywood. Double lathing is considered more effective and reliable than single-layer lathing, which is why it is recommended when installing modern soft roofs.
The structure can be assembled only from boards (sometimes bars) or from their combination with OSB and plywood.
Option #1 – double sheathing of boards
For the base under a soft roof, you can use only one type of material - boards. Both layers of sheathing are constructed from them.
Requirements for materials:
- Boards of the first (sparse) layer: thickness – at least 25 mm, width – 100-140 mm. Boards can be replaced with bars 50x50 mm or 30x70 mm.
- Boards of the second (solid) layer: thickness 20-25 mm, width – 50-70 mm.
- The lumber is pre-coated with antiseptic compounds.
Installation of the sheathing is simple and is carried out according to the following algorithm:
- First, boards or bars are nailed parallel to the ridge (perpendicular to the rafter legs) with a step that prevents bending of the boards of the second layer, on average 200-300 mm.
- From above, onto the sparse sheathing, boards of the second layer are nailed at an angle of 45° (diagonally). Not close, but with a gap of up to 3 mm, which can absorb thermal deformations of the wood. The sheathing is carried out in the direction from the ridge to the cornice.
A similar base is usually used when laying roofing felt. For flexible tiles, it is recommended to construct a combined version.
Option #2 – combined double sheathing
The combined design combines several materials. The first layer is boards or bars, the second layer is plywood or OSB.
Traditionally, the combined sheathing is assembled as follows: boards or beams are fastened perpendicular to the rafters, and sheets of plywood or OSB are placed on top of them. This technology They are used, as a rule, in the construction of a cold attic (without insulation cake and waterproofing film on the roof).
If insulation takes place, then another version of the sheathing is used, more complex. Counter battens are placed along the rafters, and on top of them, perpendicularly, are the boards of the first layer of sheathing. The entire structure is completed by plywood or OSB panels. This option differs from the previous one in the presence of a counter-lattice, which forms a ventilation gap between the large-panel flooring and the waterproofing.
Material requirements:
- Counter-lattice bars: smooth bars with a cross-section of 25x30 mm or 50x50 mm.
- Sparse layer boards: thickness – 25 mm, width – 100-140 mm.
- Plywood or OSB-3: thickness 9-12 mm.
- Materials must be pre-antiseptic.
In order to build a combined continuous sheathing, perform the following steps:
- If there is a heat-insulating cake with a waterproofing film, counter-lattice bars are installed. Their cross-section can be in the range of 20-50 mm, most often 25x30 mm. The bars are secured on top of the rafter legs, along them. The counter-lattice serves not only to form ventilation gap, but also for fixing the waterproofing film, which is laid on the insulating material. If we consider installation work step by step, then first heat-insulating mats are laid between the rafters, a waterproofing film is stretched over the rafters and mats, which is nailed on top with counter-lattice bars. If a thermal insulation cake is not expected in the roof, skip this point and immediately proceed to attaching the sparse sheathing.
- The sheathing boards (width - 100-140 mm, thickness - 25 mm) are fixed to the counter-lattice bars (if any) or to the rafters perpendicularly. The fastening step with nails (screws) is 200-300 mm.
- Sheets of OSB-3 or plywood are placed along the ridge, with the long side across the rafters. Installation is carried out with a breakdown of seams, that is, in a checkerboard pattern. A compensation gap of 2-3 mm is left between the shields. Fastening is carried out on each rafter, using self-tapping screws or rough nails for fixation. The spacing of the fastenings on the rafters is 30 cm. The slabs are laid so that their edges are sure to rest on the supports, they are joined there and also fixed with fastening elements, but with a more frequent spacing of 15 cm.
To make it clearer, look at what it looks like during the construction process:
The technology is not complicated; to understand all its nuances, just watch a short video:
Checking the design for errors
When the sheathing is ready, you should look at it with a critical eye. Were there any fatal errors that could have an impact? negative influence for roof maintenance?
A high-quality finished sheathing has the following properties:
- It does not bend under the weight of a person, otherwise it will be problematic to work on it and repair the roof in the future.
- Has no gaps (larger than permissible expansion gaps). If it was not possible to avoid gaps, then the gaps are covered with strips of roofing sheet.
- It does not have protruding knots or non-recessed nails on the surface that can break through the bituminous materials of the soft roof.
- The ends of the lumber, through which bitumen products will subsequently be bent, are not sharp, and are rounded with a plane to prevent tearing and rubbing.
- All materials for sheathing are dry and coated with antiseptic agents.
It is important that the continuous sheathing does not have the above flaws. Only in this case roll covering or bituminous shingles will successfully perform their functions.