Installation of osb boards on the roof. Lathing for soft roofing: single-layer and two-layer solid structures
In construction and renovation, various sheet materials are often used to cover walls and ceilings. One of these materials is oriented strand board (OSB), also sold under the English name OSB (Oriented Strand Board).
OSB: what is it and how to use it
OSB is made from wood chips and large shavings, gluing them together when high temperature synthetic resins.
The slab consists of several layers, usually 3-4, with different orientations of the chips.
In the outer layers, the chips are located along the long side of the sheet, in the inner layers - across. According to its characteristics, OSB is close to plywood, but costs less.
Benefits and Features
A distinctive feature of OSB is high strength, caused by the cross arrangement of wood fibers. The strength of the boards is superior to MDF, chipboard and wood, slightly inferior to plywood. The boards show high resistance to chemicals. Some manufacturers use special impregnations in the production of slabs - fire retardants, which reduce the flammability of the material. OSB boards are easy to process; to work with them you will need ordinary woodworking tools.
How OSB boards are calculated
There are mainly 2 standard sizes of slabs: 2440*1220 mm (American standard) and 2500*1250 mm (European). There are OSB in other sizes, but they are much less common and are produced mainly to order.
To calculate the quantity, the easiest way is to draw a wall plan on checkered paper, taking the size of the box to be 250 for European standard slabs or 300 mm for American ones. Then draw OSB boards on the plan and count their number. It is better to arrange the sheets in a checkerboard pattern. In this case, you need to take into account how the surface will be finished in the future.
If you plan to cover, for example, with siding on the street or gypsum board indoors, joining with non-factory cuts is allowed, but if painting is planned, try to join the slabs with factory cuts. It is advisable to reduce the number of joints to a minimum. For example, it is better to sew up a fragment of a wall measuring 2.4 m by 1.2 m with one sheet, and not with 3 pieces of 0.8 * 1.2 m, because it is ideal to produce smooth cut quite difficult, and even a slight deviation from straightness forms a gap. To the received amount of OSB you need to add several sheets as a reserve in case of defects or errors during cutting.
An easier way is to divide the surface area by the leaf area. In this case, “in reserve” it is necessary to take at least 20% of the quantity. Round the resulting number up.
What kind of OSB boards are there for external walls?
OSB is made in 4 types:
- OSB-1 - used only in dry rooms for cladding.
- OSB-2 – used as a construction material in dry rooms.
- OSB-3 – can be used both indoors and outdoors. Allowed for use in conditions with high humidity. Strength allows the use of OSB-3 as a structural material.
- The most common class is OSB-4 - more durable and moisture resistant than OSB-3.
For cladding external walls, only classes 3 and 4 can be used.
External installation: lathing
External wall cladding can be carried out in several cases:
- In order to level out existing walls, hide defects (cracks, crumbling plaster, etc.) and simply as cladding.
- At frame construction– to protect the insulation from wind and precipitation, and also as an element of the supporting system.
- When insulating walls - to protect the insulation from atmospheric phenomena.
In all 3 cases OSB sheets are attached to the sheathing. The sheathing is made from wooden lumber of various sections, depending on the task. Unplaned timber is most often used coniferous species natural humidity with a cross section of 50*50 or 40*50 mm. OSB can be attached to a metal frame.
When insulating, the sheathing is performed in steps that are a multiple of the width of the insulation minus 20 mm, without insulation - the step is chosen so that the joints of the sheets fall on the beam; several additional racks are added between the joints with a distance between them of at least 600 mm.
When covering walls, use a moisture-proof film, following the recommendations of its manufacturer, in particular, the distance between the membrane and the OSB.
How to attach panels to the wall
OSB boards are usually attached to the wall through the sheathing using wood screws when using bars in the frame or metal when attaching to a frame made of metal profile. The length of the screw should be 25-45 mm.
It is allowed to mount OSB directly to the wall. To do this, holes are drilled in a sheet cut to size, the sheet is installed in place, the wall is drilled in the designated places with a hammer drill, dowels are inserted and screws are tightened. When attached to wooden base The hardware is screwed in without pre-drilling.
Fasten the screws in one selected direction, for example, from left to right, from bottom to top, otherwise the OSB sheet may bend.
How to decorate the outside beautifully from osb
OSB has a rather interesting texture, which leaves many finishing options. At the same time, you need to remember that OSB consists of 90% wood, so the material is subject to the same dangers as wood. Fungus and mold may appear on the slabs; to a small extent they are susceptible to rotting; the resin may be destroyed under the influence of sun rays, the ends of the panels absorb moisture.
OSB boards are treated with wood compounds for outdoor use. The composition must provide UV protection. To preserve color and texture, the surface is coated with colorless varnish and antiseptic impregnations, to impart woody shades - with decorative antiseptics, for painting in various colors– facade paints for wood.
To obtain a smooth surface, OSB walls are plastered and puttied. Before applying plaster, the surface of the slab must be protected from moisture with special primers or glassine, then fixed plaster mesh and plastering. Can be applied decorative plaster or painting.
Also, OSB walls can be covered with any type of siding or facade panels, block house, clapboard, etc.
OSB material for interior work
OSB is used indoors for cladding walls, ceilings, for constructing subfloors, as a structural material in the manufacture of built-in furniture, to create decorative elements, boxes, technological cabinets. IN frame housing construction OSB internal wall cladding increases the strength of the structure.
Work progress
OSB wall cladding consists of the following steps:
- Marking.
- Lathing device.
- Laying heat and sound insulation, if provided for by the project.
- Fastening solid OSB sheets.
- Sawing OSB to size.
- Fastening the remaining sheets.
Tools
To cover OSB walls you will need:
- Hacksaw, Circular Saw or a jigsaw for cutting material.
- Screwdriver.
- Level.
- Marking tool (tape measure, square, pencil).
- Perforator for covering brick walls.
- Chisel.
Interior finishing options
The unusual structure of OSB allows you to create a rather attractive interior. The slabs can be used without finishing, but it is better to coat them with varnish to improve operational properties. OSB can be painted with wood paints or treated with decorative wood impregnations. To obtain a smooth surface, the panels need to be puttied with wood putty, after which they can be painted or covered with wallpaper.
How to properly make lathing for osb
When installing sheathing from bars, first attach the beam around the perimeter, then install vertical posts with a pitch of 406 mm with a sheet width of 1220 mm and 416 mm with a sheet width of 1250. If you need to join the sheets in height, a horizontal bar is attached at the junction.
The bars are attached to the wall in 2 ways:
- Directly through the block. When attaching to concrete, brick, cinder block and aerated concrete walls holes are drilled in the bars according to the diameter of the dowel in increments of 300-400 mm, the block is placed against the wall, holes are drilled in the wall through the prepared holes using a hammer drill, dowels are inserted and screws are tightened or anchors are used. It is more convenient to first secure the block along the edges, after which you can not hold it and calmly fasten it at the remaining designated points. When attached to wooden walls The block is attached with self-tapping screws without drilling holes. It is better to use “white” or “yellow” self-tapping screws, because If the “blacks” use too much force, the cap breaks off and it is very difficult to remove such a self-tapping screw. To adjust the frame vertically, wood linings are used.
- On galvanized corners or U-shaped fastening profiles. In this case, first mark the position of the bars, install the fastening elements according to this marking, then attach the beam with self-tapping screws.
When using a metal profile for the frame, a guide profile is attached around the perimeter, and a rack profile is attached to the plane. The profile is fastened to the wall using special hangers.
Racks and guides on the walls must be strictly vertical!
Is frame sheathing with OSB sheathing inside required?
OSB boards can be mounted directly on the wall, but it is better to use lathing. This will allow you to correct the slope or curvature of the wall, lay mineral wool to improve heat and sound insulation. The lathing also creates an air cushion, due to which the space between the wall and the OSB board is ventilated.
Installation of OSB boards
OSB is fastened with the long side vertical to reduce the number of horizontal joints. When attaching the first sheet, you should control its level position, otherwise gaps may appear in the corners of the walls. Otherwise, the fastening rules are the same as for outdoor work.
What should be the thickness
OSB comes in different thicknesses: 6, 8, 9, 10, 12, 15, 18, 22, 25 mm.
Sheets with a thickness of 6 and 8 mm are used for cladding ceilings and structures that are not subject to mechanical load. OSB boards 6 mm thick can be used for curved surfaces with a large radius of curvature.
Slabs with a thickness of 9-12 mm are the main cladding material for cladding walls and ceilings both outside and inside premises, for constructing continuous sheathing under the roof.
Material with a thickness of 18 mm or more is used for the manufacture of furniture, load-bearing structures and subfloors.
Work examples
Attic lined with OSB
Built-in OSB shelving
Relaxation corner made of OSB
Putty on OSB
Operation of OSB finishing: features
Walls made of OSB boards do not require any special care, it is enough to follow the rules common to wooden surfaces, for example, avoid prolonged exposure to moisture.
OSB is a modern high-tech material, with correct installation able to last for many years.
Useful video
Very convenient and multifunctional material for different construction work– oriented strand boards. Since the production technology of these slabs is not complicated, for interior finishing work the master can choose a specific option from four types OSB boards or consider special types of these boards.
What are the sheets of these products made of? Everything is simple - wood chips are used (flat fragments are used), shavings: these materials are glued together and the result is actually an excellent finishing material. Three or four layers of chips or shavings – these are the indicators that can be called optimal. Installing OSB on walls is more preferable than using the same chipboard.
However, oriented strand boards are a kind of modification of wood-fiber material, some of its modern analogue. If finances allow, it is better to choose OSB for facing work (plywood or chipboard are increasingly being abandoned today).
Scope of OSB, classification of boards
Before considering the classification of slabs and deciding which is the best OSB for finishing walls, it is important to pay attention to the characteristics of such a material.
Types of OSB boards
Here everything is as follows:
- OSB boards of the first class - they are usually chosen for such premises where low level humidity;
- Type two - the material can be safely chosen for dry rooms; it is even used as structural element during construction work;
- Type 3 OSB – these boards are used in rooms where there is a high level of humidity;
- The fourth type of such products is used for cladding structures that can cope even with significant mechanical loads. Moreover, we are talking about conditions where there is a high level of humidity.
Application area
One thing can be said about the scope of application - installation of OSB is a truly urgent task, since such boards are used in many construction aspects.
It’s just that this material has such a manufacturing technology, due to which everything internal defects are simply excluded (at the same time, in chipboard sheets they often appear - voids, uneven filling). Due to all this, OSB is a more preferable option - it does not deform and does not shrink.
And now in detail - where exactly can this material be used??
- OSB cladding for walls is often very profitable solution. Due to this approach, the house receives reliable protection from dampness, while also gaining additional insulation. What's best here: in additional finishing works there is no need after installing OSB;
- In the construction of frame-panel houses, OSB boards are usually used, which have high level moisture resistance;
- Since the material has such valuable quality, it makes a decent reusable formwork;
- It is used as a base when making external cladding walls, as well as internal works– if wooden finishing is carried out country houses, cottages (made of timber, rounded logs);
- OSB boards are yours faithful assistant, if you are making sheathing, rafters for the roof. This material can work even under serious load - it will definitely withstand the weight of not only the roof itself, but also all associated loads (wind, snow) - even if natural tiles(material that weighs little);
- If you need to level the floors in your house or lay them from scratch, here again you can pay attention to the installation of OSB. Just such a slab - perfect option to create a very strong, even base. It’s better not to find it under plank floorboards, carpets or other coverings;
- Pay special attention to the process when you need to adjust the joints of the slabs to a plane. If necessary, they must be equalized - without this there is no way.
An interesting point - not every manufacturer can use OSB boards as underlying layers - in the case of floor coverings. And the panels are laid so that the smooth side is facing up.
What else does a master need to know?? Following:
- There is no need to apply an additional protective coating in the form of paint or varnish to the slabs - the material initially has excellent protection in the form of a special impregnation;
- Processing slabs is not that difficult - about the same as regular wood. Screws and nails adhere perfectly to the surface. OSB boards are not afraid of rotting, fungal influences, the decorative qualities of such material are excellent;
- OSB panels today are often used in furniture production– after all, this is an excellent alternative to natural solid wood(but in terms of cost, it is significantly more profitable);
- The material does not weigh that much - therefore it is perfect for finishing, construction, painting work and more.
How to finish a house faster
It is quite logical that any owner wants to move into his home faster - especially if the construction is carried out independently. Private cottages are located separately from neighboring buildings - so in this design you don’t have to worry about neighbors.
Here a completely justified question may arise: maybe you shouldn’t do the rough sheathing - but immediately attach the finishing OSB materials directly onto the frame posts?
Is this approach to the matter allowed, or is it excluded?
If you pay attention to the instructions compiled by professionals, it will immediately become clear: you cannot do this. There will also be reasons for this conclusion. Simply, it is important to insulate the house - only in this situation will it be comfortable (especially since winters in the Russian Federation are cold - almost throughout the entire territory).
Why are frame bevels required at all - lower and upper? Everything is simple here: they form spatial rigidity - together with the cladding. They can also be called mandatory elements if we consider the design of any frame structure.
A frame that does not have slopes will retain its mobility even with cladding - as is the case when there are any. However, if there is no cladding, you can imagine what the consequences might be.
External rough wall cladding
A lot is used today for rough cladding. different materials. There is definitely a choice here - everyone will agree with this. Pay attention to at least these options:
- Board;
- OSB boards.
Any of these surfaces needs finishing: this could be facing with plaster - with a mesh or a layer of polystyrene foam. There is an opinion that even the boarding can be left as a finishing touch - but in this case the wood will need to be processed additionally. Hydro-wind protection of the walls is also installed under the boards.
You must take into account the following: it is not recommended to finish the frame with boards - without rough, preliminary covering with OSB boards. Otherwise, there is a risk that the boards will come loose in the fall or spring. In addition, this is important for the spatial rigidity of the frame.
You will get fewer joints due to the area of OSB sheets - which cannot be said about working with other materials. OSB finishing is usually made with a material whose thickness is 11-13 mm.
Let's take a closer look:
- The OSB boards are fastened to the racks so that there is a joint in the middle. And there should be a small gap between the plates - three to five millimeters is enough;
- The sheet completely covers the lower trim;
- Closely related to the number of storeys of the building top harness. It will be completely hidden - and the edge of the OSB slab will be aligned with the edge of the trim if the structure has only one floor;
- When a building consists of two floors, the sheet is positioned as follows: it must fit onto the racks of both floors at once. But somewhere in the middle of the sheet the top trim overlaps. This condition cannot be called mandatory, but if it is fulfilled, the rigidity of the structure increases noticeably, which benefits the structure;
- Sheathing with OSB boards, when fastening to a window opening in two-story houses is carried out, should be done in a single sheet - this is exactly what the professionals advise. Then all the joints can be moved to adjacent racks outside the racks of the opening. They simply cut through the slab window hole– there is nothing complicated in such work. Here https://krepezhmaster.ru you can purchase fasteners for absolutely any purpose;
- When horizontal or vertical jumpers are made in the frame, a very convenient joining of the slabs is obtained. In the event that these jumpers have the same cross-section as the racks - and this often happens;
- Spiral nails are selected for fastening. Self-tapping screws are also suitable - 0.5 or 0.45 cm long. You should also not refuse combined fasteners (both nails and self-tapping screws) - such a solution is considered to be of very high quality.
Remember that basic rules for performing fastening work must be observed.
Namely:
- It is customary to fix the finishing of OSB slabs in intermediate areas every 300 mm;
- After 150 mm, fix the places where the slabs are joined;
- After 100 mm it is necessary to sew the outer edge.
To prevent cracks in the material due to too zealous fastening, a distance of 1 cm is maintained from the edge of the slab to the place of fixation (a little less is possible).
- A gap of 4-5 millimeters is left between the plates so that they do not warp. The fasteners are driven 4-5 cm into the rack;
- The part of the OSB board that is vulnerable (one might say this is the "Achilles' heel" finishing material) – ends. To ensure the protection of these areas, gaps are provided, which are called expansion gaps (between the crown beam and the upper edge, also between the foundation wall and the lower edge). Here the gap will be 10 mm. And between those slabs where there is no tongue-groove, 3 mm is quite enough;
- To seal these expansion gaps, apply a sealant to acrylic base. It is important that it carefully fills all the cavities - and that this work is done evenly;
- Wind protection, waterproofing - all these tasks will be performed by a superdiffusion membrane, which also has the property of vapor permeability (this indicator is 750 g/m² or more).
Craftsmen do not recommend using polyethylene, various films, glassine. It’s just that these materials have a low level of vapor permeability; all excess moisture must be reliably ventilated.
Also, you should know:
- The superdiffusion membrane is installed depending on the rough lining with materials, what it is fine finishing. For example, the membrane is often attached closely to the insulation - to the frame studs;
- They make a sheathing (here they use wooden slats, the cross-section of which is 2 by 5 or 3 by 5 cm. Thanks to this design, the required gap will be achieved. Then you can finish OSB surface slabs, SML, DSP or sheathed with boards;
- From the inside of the room, you can use film to create a vapor barrier for the walls. The material is installed in such a way that it fits tightly enough to the insulation. A construction stapler is used for fastening. The joints are overlapped - 150-200 mm; the joints must be taped.
For such work, you can choose the simplest adhesive tape - there is no need to use construction material. Vapor barrier adhesive tape will also work.
- To perform a vapor barrier, you can use foiled polyethylene, which will not thicken the wall thermal insulation (basic). Foam material is also often used for this task - this practice is common in our time.
Finishing the structure inside
Which is better: OSB sheathing or plasterboard cladding? Many are clearly inclined to favor option number one - when it comes to interior finishing work in the house. It is quite difficult to keep the frame posts in a completely level state - when work is underway, the same applies to drywall.
It’s just that the sheets of this material are softer when compared with osb boards. They will easily repeat all the irregularities - so then you will have to work hard to get a completely flat surface - more layers will need to be applied to level them.
OSB board is an order of magnitude stiffer in structure than plasterboard sheets, so all flaws can be smoothed out to a certain extent. Afterwards they begin to carry out work related to finishing.
Watch a video about how OSB boards are used for interior decoration premises. This material will definitely be useful if you do not have much construction experience.
OSB-3 boards and roofing work
Roofing work is a very popular way to use materials such as OSB boards. By the way, to cover the roof with OSB-3 slabs, a material thickness of 0.18 cm is sufficient.
In order:
- Products can have both a locking edge and a straight edge. The first option is more preferable;
- Between load-bearing beams the distance should not be more than 609 mm - this applies to both the organization of sloping and flat roofs;
- Whether the slabs are capable of expanding is of great importance. For each linear meter It is customary to leave a gap: 2 mm is quite enough (believe me, this is enough);
- When laying slabs with smooth edges, the gap is made a little larger - 3 mm. Leave it around the perimeter of each slab - this is the only way to achieve optimal results;
- Nails are used to attach OSB to the roof. Attached to supporting supports. There should be a distance between them: 10 cm or even more;
- The finishing of OSB boards is attached with nails - they should have a length that exceeds the thickness of the board by two to two and a half times (or even more) - this is quite normal.
If the interior decoration is done using OSB panels, the following can be noted: a slab made of polished panels will look better if it is very important in your space appearance. It is better not to use such slabs for finishing. ceramic tiles or wallpaper - this is what the manufacturers themselves recommend. And it’s best to listen to their opinion!
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 hard 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 made 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, as 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 wet 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 ridge 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 them to the rafters panel materials– 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 covering of the roof with waterproofing materials. 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 junctions 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 a ventilation gap, but also to fix the waterproofing film, which is laid on the insulating material. If we consider the installation work in stages, 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 bitumen shingles will successfully perform their functions.
Soft roofing in last 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 a regular 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 device is also provided at the ends pitched roof, 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 the similarity with the frame for other roofing materials ends. Under rigid sheets roof sheathing can be made from Not 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 run, 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 thing 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 break, 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. Preparation truss structures roofs 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 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:- Solid flat smooth surface bases without deflections, potholes, chips, cracks and protruding chips or nails.
- Technical gaps between OSB boards or plywood sheets, 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.