Roof from osb sheet to cover or not. Is moisture dangerous for OSB plywood? Do you need additional processing

02.12.2012, 21:08

Dear forum users need advice. For the winter, there is a roof under OSB 9mm. The house is made of gas silicate, there is a rafter covered with a Eurovent membrane, covered with a counter-lattice, a crate with a pitch of 30 cm. At the top of the OSB 9mm. Partially a valley carpet is laid, the roof is accordingly not insulated and the house is not heated. The roofers, having received half of the money for the entire turnkey roof, refused to carry out further work, citing bad weather.
Help make the right decision.
1 Cover the roof with cellophane with nailed slats (there are fears that moisture from OSB under unventilated cellophane will destroy OSB)
2 Cover the roof with some inexpensive membrane that allows air to pass through and retains water.
3 Attract a new team and cover with flexible tiles until they finish snow and frost (it is embarrassing that the OSB base is wet and under the sealed tiles it will trample and deform, then collapse)
4 Leave everything as it is. But none of the acquaintances have experience with an uncovered OSB.
Old roofers say to wait for spring and not cover anything, the new team - they really need work, they say that it is possible to lay down on a wet one and up to -5 frost with a hairdryer.
I wanted to hear objective opinion uninterested specialist, thanks in advance

Good day!
We build frame house, it is sheathed with OSB plates, there is a roof - corrugated board, in the winter it will go in this form. During the summer, after several rains, the OSB stratified in some places. Is it possible to cover the walls with a windproof film under the future ventilation facade for the winter and will it not lose its properties by spring? And what material is better to take: Izospan A, AD? The facade will be a blockhouse.

It is possible to cover an unprotected facade with a windproof film, but this will not completely solve the problem of preserving OSB. The fact is that the windproof membrane is designed to withstand the effects of individual drops, which are the result of condensation on roofing... Good slanting rain, downpour, sleet is beyond her power, the windproof membrane will "cry" with inside... Undoubtedly, wind protection will reduce the wetting of the OSB, but it will not completely eliminate it.

A windproof membrane is a good thing when it is covered with an outer trim

OSB-3 boards, which, most likely, will sheathe the frame of your house, can be called moisture resistant only with a stretch. And then about their resistance to moisture can be said only in relation to chipboard, fiberboard, OSB-1 and OSB-2, which quickly collapse under the influence of water. OSB-3 is not intended to be used as a sheathing wall material without further finishing, unlike, for example, cement particle boards(DSP). By the way, in Canada and the USA, where did they come from? frame technologies, for the decoration of decent houses that must stand for a long time, use waterproof plywood, particle boards- the lot of the poorest.

Manufacturers give such characteristics as the degree of swelling of an oriented strand board when in water for a day. For OSB-3 it is 15%. This is not so little, contrary to the claims of sellers and manufacturers. Of course, on the walls, the particle boards are in an upright position and are only exposed to the slanting rain on one side. However, let us assume that there are showers, sleet, wet for a week or two. The low air temperature and the absence of the sun do not allow the walls to dry out.

OSB sheets that are not protected from precipitation will get wet and swell properly. At the same time, they will increase not only in thickness, but also in length and width, albeit not so significantly. As a result, the particle boards, which are rigidly fixed to the frame, will warp. And it's not a fact that when they dry they will take their original shape, permanent deformations are very likely. In addition, the attachment points will weaken, delamination of the ends may occur (it has already begun for you), the strength of the gluing will decrease. It is unlikely that critical damage will not be inflicted on particle panels in one season, but their service life will be reduced, the overall stability of the frame will decrease, this is a fact.

OSB is not a completely waterproof material, it will inevitably collapse with prolonged exposure to moisture

In our opinion, for temporary protection of an unfinished facade from precipitation, it is possible the following options:

Pull on windproof membrane Izospan A (18 rubles / m2) on a vertical crate, use a bar 4-5 cm thick. The film is rather weak, it is not a fact that it will successfully survive the winter, it will not be torn by the winds.
Use Izospan AM (24 rubles / m2) or Izospan AS (35 rubles / m2). A three-layer windscreen is stronger, less water vapor permeable, but three times more waterproof, which means it will get wet less. Under the finishing (blockhouse), it could be stretched without lathing, right along the slabs. But in your case, a ventilated gap and crate are needed. It is necessary to ensure a free flow of air, the gap should be below and above, under the roof. Option number 2 is preferable.
Stretch along the lathing, observing ventilation, any vapor-waterproofing material is cheaper: roofing paper, construction reinforced vapor barrier, dense plastic wrap for greenhouses (enough for one season). When cladding the facade, the waterproofing will have to be removed.

While there is no finishing, plastic wrap can be used as temporary protection, with or without reinforcement.

The right decision would still be to tighten up with finances and finish by the fall. exterior decoration, sheathed the facade with a blockhouse along the vertical crate. As a result, it will come out cheaper, because the OSB boards themselves can serve as wind protection, if they are neatly fitted. You don't have to spend money on film.

Correct solution Puff pastry frame wall... If the OSB boards are fitted well and the insulation is completely closed, they will also serve as wind insulation. There is no need to spend money on an additional membrane.

Master Tips

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There are many types of soft roofing. It includes numerous roll-on weldable materials, soft tiles and roofing felt. These materials may have different performance and visual characteristics, but they also have common feature- all of them are made on the basis of bitumen, due to which the softness and flexibility of the final product is ensured.

With all its flexibility, a soft roof can retain its shape once given and withstand various loads - but in order for these properties to manifest, it is necessary to equip a high-quality and reliable crate under the roof. How to make a crate under a soft roof, and will be discussed in this article.

Types of sheathing for soft roofs

There are two fundamentally different kinds- solid lathing and lattice. In a lattice crate, all elements are located at some distance from each other. As a rule, the pitch of installing boards in such a crate varies from 20 to 50 cm. For soft roofing materials, this design is not suitable - the gaps between the boards are too large, so the roof will sag in them.

A completely different matter is the solid crate, in which, as the name suggests, the gaps between the elements are absent or minimized. The maximum pitch of the sheathing for shingles in this case is 1 cm.

Two types of solid sheathing can be installed under a soft roof:

Single layer... In this design, the sheathing elements are installed directly on the rafter legs and are located parallel ridge run... Boards, moisture-resistant plywood or OSB are suitable for installing a single-layer lathing. This design is used quite rarely and only if the roof is covered with roofing felt.
Double layer. This kind the lathing consists of two layers, which can be made from one material or from different ones. First, a rafter system is installed under a soft roof, then the first layer is arranged as a lattice, with a rather big step installation of elements. A second layer is mounted above it, in which gaps are not allowed. The main advantage of a two-layer lathing is the presence ventilation duct and free space sufficient for styling thermal insulation materials, which makes this structure very convenient for arranging a soft roof.

The installation technology for each type of lathing is worth considering in more detail.

Single-layer sheathing from boards for shingles

As mentioned above, a single-layer sheathing for shingles is attached directly to the rafters and is only suitable for laying roofing material. In addition, when using such a structure, it will not be possible to install insulation, therefore, from the point of view of energy efficiency, a single-layer lathing is not very good.

The frame for a soft roof can be made of grooved boards or timber. Choose unedged boards extremely undesirable - any roughness and unevenness of this material will necessarily lead to deformation of the soft roof, which, in turn, will lead to a decrease in their decorative and performance characteristics.

When choosing boards, you need to build on the following requirements:

The material should have a flat and smooth surface without any irregularities;
The width of the boards can vary within 100-140 mm, and the thickness - 20-37 mm;
The moisture content of the boards should not exceed 20% (excess moisture in the wood leads to its premature deformation and damage to the roofing);
Before making the crate, all wooden elements it is necessary to impregnate with antiseptics that will protect the wood from decay, mold and pests.

Structurally, the considered single-layer crate is a board that is stuffed to the rafters end-to-end. The boards should be placed parallel to the skate. So that they do not warp over time, they must be laid with the concave side up, so that moisture that has made its way through the thickness of the roof covering flows through the boards through the cornice.

It is necessary to start the process of installing the lathing from the eaves, gradually moving towards the ridge. The length of the boards must be selected so that they dock exactly on the rafter legs. It is advisable to fasten them as close to the edge as possible, hammering nails into the tree to the very head.

The optimum gap between vertical adjacent boards is 3 mm. The presence of such a gap, on the one hand, will provide reliable support for a soft roof, and on the other hand, it will allow the boards to freely change their dimensions when temperature and humidity change. If you fix them more densely, then the constant expansion and contraction of the boards will sooner or later lead to their curvature.

Single-layer lathing made of panel board materials - step, frame thickness

For arranging the lathing, you can use not only boards, but also panel materials - plywood or OSB. They have all the necessary qualities that are required for high-quality support structure... In addition to good performance characteristics, plywood for shingles is easy to install and has a flat surface ideal for further installation of soft roofing.

A number of requirements are also imposed on the shield materials used in a single-layer crate:

High moisture resistance... The soft roof must be reliably protected from moisture, therefore, moisture-resistant materials must be selected for the lathing. If we talk about specific brands, then we can distinguish OSP-3 and FSF.
Suitable thickness... Panel materials can have a thickness of 9 to 27 mm (the choice of a specific size depends on the pitch of the rafters).
Antiseptic treatment... In order for the crate made of panel materials to be sufficiently durable and reliable, it must be treated with an antiseptic before laying.

Laying panel materials on rafters is not done in the same way as in the case of boards. The sheets are mounted parallel to the ridge, but their joints should not overlap. Usually a checkerboard arrangement is used for such material.

Adjacent sheets should be at a distance of 2 mm from each other. When installing the roof in winter, the step should be increased to 3 mm so that the lathing can freely expand in summer time... To fix the shields, self-tapping screws or nails are used, which are used as follows: on the rafters, the fastening step is 30 cm, on the end sections they are located 15 cm from each other, and at the edges - 10 cm.

Double solid board crate

A two-layer lathing consists of two layers, one of which is made in a lattice form, and the second, located at the top, in a solid one. This design of the lathing is more reliable and efficient than a single-layer one, therefore it is used in the overwhelming majority of cases. Of course, due to the greater number of layers, the thickness of the soft roof increases.

In the considered option, each layer of the sheathing consists of boards, which must meet the following requirements:

The boards of the lattice layer should have a thickness of over 25 mm and a thickness of 100 to 140 mm (instead of boards, you can use beams with a section of 50x50 or 30x70 mm);
For the manufacture of a continuous layer of lathing, boards with a thickness of 20-25 mm and a width of 50-70 mm are required;
Before laying, wooden elements must be treated with antiseptic agents.

Installation of a two-layer lathing is quite simple. First of all, boards of the first layer are attached parallel to the ridge across the rafters. They need to be fastened at such a distance that the second layer does not bend after installation. The optimal installation step for the boards of the first row is 20-30 cm.

When the first row is mounted, you can start installing the second. You need to mount the crate elements from top to bottom. A small gap of 3 mm should be left between the boards for normal thermal expansion.

Combined two-layer roof batten

For styling shingles best suited combined option lathing, in which the first layer consists of sparse boards, fixed perpendicular to the rafter legs, and the second one is made of shield materials. This type of construction is standard and is most often used when arranging an unheated attic.

To create an insulated attic with waterproofing and insulation, you will need a different scheme, somewhat more complicated. First, you need to fill a counter-lattice along the rafters, and all other elements will be attached on top of it. Let's see what the counter-grill is for in general. Counter-lattice slats allow you to create ventilation gap between the main batten and the waterproofing material.

The materials used must meet the following requirements:

For counter-lattice, even bars with a section of 25x30 or 50x50 mm are suitable;
The first layer is equipped with boards 25 mm thick and 100 to 140 mm wide;
Plywood or OSB under soft shingles must have a thickness of 9 to 12 mm;
All wooden elements must be impregnated with an antiseptic.

The installation of the combined lathing is carried out according to the following algorithm:

When arranging warm roof with insulation and waterproofing, you need to install a counter-lattice, which is attached above the rafter legs. Besides creating a gap for ventilation roofing cake, counter-lattice bars provide fastening waterproofing film... To create such a structure, first of all, it is necessary to install thermal insulation and waterproofing, and only then proceed with the installation of the battens.
Next comes the turn of the boards of the first row, which are attached to the counter-lattice (if any) or directly to the rafter legs. The standard step for fixing the bottom layer of the lathing is 20-30 cm.
V last the last row of the crate is installed. Sheets of the selected material are stacked in a checkerboard pattern with a small gap (2-3 mm). OSB or plywood for soft tiles is attached to each rafter leg with a step of about 30 cm. The edges of the elements must also fall on the supports, and at these points the fastening step must be reduced to 15 cm.

Checking the quality of the lathing

If the crate is under bituminous shingles was mounted correctly, then it will have a number of properties:

No deflection under human weight - sagging elements of the sheathing will significantly complicate the installation of the roofing and its repair;
Absence of gaps in excess of the permissible limits (if there are large gaps in the crate, they must be repaired roofing sheet);
The absence of irregularities, protruding nails or knots, which can violate the integrity of the soft roofing material;
Absence of sharp edges around the entire perimeter of the finished sheathing;
Qualitatively conducted preliminary preparation wood, which includes drying boards and sheets, as well as impregnating them with antiseptics.

Roof lathing for soft roofing is considered complete only if it meets all the requirements described.

Conclusion

Several types of sheathing are suitable for a soft roof, therefore, before making a sheathing for a soft roof, you need to choose suitable design... If all the nuances have been taken into account, then it remains only to correctly conduct assembly work, and finished structure will provide reliable support for the soft roof covering.

Good day!
We are building a frame house, it is sheathed with OSB plates, there is a roof - corrugated board, in the winter it will go in this form. During the summer, after several rains, the OSB stratified in some places. Is it possible to cover the walls with a windproof film under the future ventilation facade for the winter and will it not lose its properties by spring? And what material is better to take: Izospan A, AD? The facade will be a blockhouse.

It is possible to cover an unprotected facade with a windproof film, but this will not completely solve the problem of preserving OSB. The fact is that the windproof membrane is designed to withstand the effects of individual drops, which are the result of condensation on the roof covering. Good slanting rain, downpour, sleet is beyond her power, the windproof membrane will “cry” from the inside. Undoubtedly, wind protection will reduce the wetting of the OSB, but it will not completely eliminate it.

A windproof membrane is a good thing when it is covered with an outer trim

OSB-3 boards, which, most likely, will sheathe the frame of your house, can be called moisture resistant only with a stretch. And then about their resistance to moisture can be said only in relation to chipboard, fiberboard, OSB-1 and OSB-2, which quickly collapse under the influence of water. OSB-3 is not intended for use as a cladding wall material without subsequent finishing, in contrast, for example, to cement-bonded particle boards (DSP). By the way, in Canada and the USA, where frame technologies came to us, waterproof plywood is used to decorate decent houses that must stand for a long time, particle boards are the lot of the poorest.

OSB is not a completely waterproof material, it will inevitably collapse with prolonged exposure to moisture

In our opinion, the following options are possible for temporary protection of an unfinished facade from precipitation:

Stretch the Izospan A windproof membrane (18 rubles / m2) along the vertical crate, use a block 4-5 cm thick. The film is rather weak, it is not a fact that it will successfully survive the winter, it will not be torn by the winds.
Use Izospan AM (24 rubles / m2) or Izospan AS (35 rubles / m2). A three-layer windscreen is stronger, less water vapor permeable, but three times more waterproof, which means it will get wet less. Under the finishing (blockhouse), it could be stretched without lathing, right along the slabs. But in your case, a ventilated gap and crate are needed. It is necessary to ensure a free flow of air, the gap should be below and above, under the roof. Option number 2 is preferable.
Stretch along the crate, observing ventilation, any vapor-waterproofing material is cheaper: roofing paper, reinforced construction vapor barrier, dense plastic film for greenhouses (enough for one season). When cladding the facade, the waterproofing will have to be removed.

While there is no finishing, plastic wrap can be used as temporary protection, with or without reinforcement.

The correct decision would still be to tighten up with finances and finish the exterior finish by the fall, sheathing the facade with a blockhouse along the vertical crate. As a result, it will come out cheaper, because the OSB boards themselves can serve as wind protection, if they are neatly fitted. You don't have to spend money on film.

Correct solution of the "puff pastry" of the frame wall. If the OSB boards are fitted well and the insulation is completely closed, they will also serve as wind insulation. There is no need to spend money on an additional membrane.

Oriented strand board (OSB), which is used inside a dry room, does not need any additional protection from moisture. In the worst conditions, the outer cladding of a house from this slab turns out to be. Over time, it darkens not only from rains, but also from solar ultraviolet radiation. Of course, it is possible to close the slabs with siding or a blockhouse, but this is associated with high costs. How to process an OSB (OSB) board from moisture is not an easy question. We will try to answer it.

Do you need additional processing?

The moisture resistance of oriented strand boards is characterized by the amount of swelling in thickness during the day. According to this parameter, according to the American PS 2 standard, the European EN-300 and the Russian GOST 10632-89, the plates are divided into 4 types (see table).

Recall that for outer cladding buildings, only OSB-3 and OSB-4 slabs are allowed.

If the constructed structure still somehow gets off, then during the construction of the OSB slabs lie on the construction site in packs. Even after one rain, several of the top sheets swell almost one and a half times. They will remain so even after drying. The rest of the sheets swell at the ends. By the way, in order to avoid this, the ends of North American products are painted with a blood-red impregnation.

It is believed among some builders that OSB slabs do not need additional processing, since they are already impregnated with resins, waxed, varnished. Experience shows that after 2-3 years their appearance loses its original freshness, they darken, in some places individual chips bulge out, the joints protrude sloppily.

Therefore, additional hydrophobic treatment will not be superfluous, especially if it is a facade of a residential building without any cladding. Consider how to treat the OSB board from moisture.

1. Transparent impregnations

The cheapest treatment option is water repellent colorless impregnations... There are no special solutions for OSB. You can use any wood product, except for those prepared on water based... Examples of such formulations:

Elcon wood preservative, silicone-based. Designed for long-term protection wooden structures from atmospheric influences, decay, mold. Scope: for indoor and outdoor use. Forms a water-repellent film, non-toxic, allows the tree to "breathe".
Innovative domestic hydrophobizing composition NEOGARD-Derevo-40 based on organosilicon oligomers. Designed to impart water-repellent properties to products made of wood and materials based on it: plywood, chipboard, fiberboard. Water absorption for chipboard is reduced by 15 - 25 times. Obviously, it works for OSB too. Does not change the natural color of the material, protective properties persist for at least 5 years.

The most suitable for protecting wood (and OSB) from moisture is the so-called yacht varnish on a urethane-alkyd or alkyd-urethane base. Some of the popular brands:

Tikkurila UNIKA SUPER (Finland). This brand is the leader in resistance to impacts external environment, immunity to ultraviolet radiation and temperature changes.
Marshall protex (Turkey). Creates a plastic surface film.
Marshall Protex Yat Vernik. Possesses increased wear and moisture resistance.
PARADE (Russia). Keeps fresh for a long time.
Belinka Yacht (Russia). Possesses dirt and water-repellent properties, emphasizes the texture of wood-based materials.
Wood antiseptic varnish "Drevolak" on acrylic base with the addition of wax (Russia). Along with antiseptic and antibacterial action, it successfully protects wood from moisture.

Since OSB is a product of wood processing, then paints and varnishes(LMB) the same can be used for them:

Oil paints. Due to the presence of polymer resins in the OSB, varnish-based paints do not always fit well on the surface to be painted. For better adhesion to the substrate, it is recommended to make two priming with an intermediate putty before painting. Despite this, oil-based paints and varnishes under the influence of ultraviolet radiation, temperature extremes and atmospheric precipitation are prone to fading, cracking, and even peeling. We can recommend a paint based on natural and modified oil PINOTEX WOOD OIL SPRAY, which has good resistance to external factors.
Alkyd paints better match chipboards, since they contain an alkyd resin, as a product of the chemical interaction of natural oils with acids. Their adhesion is higher in comparison with oil paints, they dry faster and more successfully resist atmospheric influences.
Acrylic compositions, being inexpensive and durable in operation, are distinguished by an optimal ratio of qualities and are most in demand for painting wood. In addition, they are available in a large assortment of colors.

Attention: pre-process small surface in an inconspicuous place to make sure that the aqueous acrylic slurry does not swell the material.

In conclusion, we can say that the question: how to treat OSB (OSB) board from moisture, is difficult to answer unequivocally. Firstly: it depends on whether you want to emphasize the texture of the board with a transparent solution or, conversely, apply a covering (opaque) coating. Secondly: - from financial capacity and aesthetic views of the developer.