The construction or renovation of the roof always requires careful planning of each stage of work, especially when the main coating is chosen. flooring. One of the most popular types of this material is the profile. MP 20It combines high load-bearing capacity and aesthetic appearance. However, the durability of the entire structure depends not so much on the sheet itself, but on the quality of preparation of the base on which it fits.
It's the right fit. crib It takes on wind and snow loads, transferring them to the truss system. Errors in step calculations or lumber selection can lead to deformation of metal roofing, leaks and even destruction of the roofing pie. In this article, we will discuss in detail the technical requirements for the base of the MP 20We will consider the mounting schemes and answer frequent questions of builders.
You need to take into account that MP 20 has a wave height of 18 mmThis is a universal, but not the most severe, coating. This dictates its conditions by the frequency of the location of the supporting elements to exclude the deflection of metal between the bars. Ignoring these parameters will make the operation of the house problematic in the first winter.
Characteristics of the MP 20 and requirements for the base
Profile MP 20 is made by cold profiling method of galvanized steel with polymer coating. Its geometry is a trapezoidal wave that provides stiffness to bend. Despite the presence of ribs, a thin metal (usually between 0.4 and 0.55 mm) is not able to withstand the weight of a person or snow cap without support.
The main task of the crate is to ensure a uniform distribution of loads. If the step of the bars is too large, under the influence of snow, the leaf will bend between the supports. This will lead to a violation of the tightness of the joints and a possible separation screw-driver. In addition, constant deformation of the metal causes microcracks in the polymer layer, triggering the corrosion process.
- 🏗️ Structure capacity: It depends on the thickness of the metal and the pitch of the supporting elements.
- ❄️ Snow load: The main factor determining the density of the crate in your region.
- 🌬️ Wind pressure: It requires a reliable attachment of each sheet to the timber.
For different types of constructions, the base requirements may differ. If small deviations are allowed for outbuildings, then a residential house requires strict compliance with the law. SNIP and the manufacturer's recommendations. It is also important to consider that MP 20 It is often used not only for roofing but also for wall cladding, where the crate pitch requirements are less stringent.
Selection of material for crate: timber or board?
The classic and most reliable solution for roofing is the use of a trimmed board. Most often used board thickness of 25 mm or 32 mm and width of 100 mm. Wood should be well dried (humidity not more than 20%), otherwise in the process of drying it can lead that will violate the flatness of the roof.
An alternative to the board can serve as bar 50x50 mm cross-section. This option is more often used in regions with extremely high snow loads or when installing insulated roofs with a heavy pie. The beam provides greater rigidity, but requires a more powerful truss system, as it is heavier than the board itself.
⚠️ Attention: It is not recommended to use a hunchback, an uncut board with bark or a material with deep cracks and rot. These defects drastically reduce the bearing capacity of the structure and are an ideal environment for pests to breed.
Before installation, all wooden elements must be processed. flame-proofing and antiseptics. This will protect the frame from fire and biological destruction. Processing is better to carry out before installing elements on the roof to soak up all hard-to-reach places that will be hidden after installing the profile sheet.
Buy a board with a margin of 10-15% for trimmings and marriage. Better to keep the material than have to look for identical in the midst of construction.
Calculation of the step of the crate under the profile sheet MP 20
The step of the crate is the distance between the centers of the neighboring bars. For profile MP 20 this parameter directly depends on the angle of slope and the estimated snow load. The more the roof is laid, the more often the supports should be located, since the snow from such surfaces comes down worse.
There are three main schemes of arrangement of elements: sparse, standard and solid. Rarely used on steep slopes in warm regions. The standard is the most universal option. A solid crate (from a board or a board) OSB-plate) mandatory for endes, around chimneys and overhangs.
Below is a table that helps determine the optimal step depending on the operating conditions. Data are advisory in nature, for complex projects requires a separate calculation.
| Skat angle | Snowy area | Recommended step (mm) | Crate type |
|---|---|---|---|
| 10 degrees. | Anybody. | It's all over. | Board/Phanera |
| 10 - 15 degrees | Medium/High | 300 - 400 | 32x100 board |
| 15-30 degrees. | Low/Mediocre | 400 - 500 | Board 25x100 |
| More than 30 degrees. | Anybody. | 500 - 600 | Board 25x100 |
When calculating the step, it is important to remember cornice. The first bar at the cornice is always installed more powerful (often 50x100 or 50x150 mm), as it holds the weight of the entire hanging part of the roof and takes the main blow when the water drains. The distance from the edge of the cornice to the center of the first timber is usually 250-300 mm, but may vary depending on the length of the overhang.
Installation technology: step-by-step instructions
Installation begins with laying waterproofing membrane over the insulation or the rafters. Between the film and the board of the crate must remain a ventilation gap height of 30-50 mm. To do this, the rafters are first nailed to the counterbars, and the main bearing row is already stuffed across them.
Fixing the board to the rafters is carried out with the help of nails or screws. The length of the fastener should be 2-3 times the thickness of the board (for 25 mm of the board - nails 70-80 mm). It is important to use galvanized fasteners so that rust does not flow down the tree and weaken the connection.
☑️ Checklist before installation of the profile list
The first row of the crate should be strictly parallel to the cornice. Any deviation will lead to the fact that the sheets of profnatsya go "wave", and it will be impossible to correct this. For control, use a strained lace or laser level. Subsequent rows can be mounted using a template from the trimming of the board of the desired length.
⚠️ Note: Do not skimp on the fastener for the crate itself. The use of rusty nails or too short screws will lead to loosening of the structure under wind loads.
Features of the device of the cornice node and overhangs
The cornice overhang is an area of increased risk. Here snow accumulates, here water drains, and here most often formed. icicles. Therefore, the first element of the crate is always made more massive. If the main crate is made of a board of 25x100 mm, the cornice board must be at least 50 mm thick.
The height of the first bar also requires attention. Because proflexion MP 20 has a certain wave height, when installing the lower row of screws will twist into the sole of the wave. To the sheet does not sag on the cornice, the axis of the first beam should be raised relative to the axis of the second by an amount equal to the height of the profile plus the thickness of waterproofing (usually about 20-30 mm).
To ensure proper drainage to the first beam is attached dropper. This is a metal bar that directs condensate from under the roof directly into the gutter, bypassing the frontal board. Without an IV, the wooden front board will quickly rot from constant contact with moisture.
Properly designed cornice unit with reinforced crate and dropper extends the life of the entire roofing system for 10-15 years.
Frequent Mistakes and How to Avoid Them
One of the most common mistakes is the violation of geometry. If the boards of the crate have different thicknesses (for example, a batch of 25 mm and 28 mm), the roof plane will be wavy. On a metal profile, this will be noticeable even to the naked eye, especially in lateral lighting.
Another problem is the lack of ventilation. The tight adjoining of the board of the crate to waterproofing (without counter-crate) blocks the release of moisture from the under-roof space. This leads to wet insulation, reduced its efficiency and rotting of wooden structures of the truss system.
- 📉 Savings on the move: increasing the step above the norm for the sake of saving the board leads to deformation of the profile.
- 🔨 Wrong fastener: putting nails too close to the edge of the board causes it to split.
- 💧 Ignoring waterproofing: Installation of the crate directly on the rafters without film is permissible only for cold attics with good ventilation.
They often forget about the alignment of the ends. If the roof slope is long, the boards of the crate can "go" away towards the skate. Before mounting the profile sheet, it is necessary to check the end line and, if necessary, saw off the protruding parts along the strained thread to get a smooth fronton.
What to do if the board is curved?
If you find a curved board after buying, do not try to straighten it by force. It is better to use it on short areas in less noticeable places (closer to the skate or near the gable) or use it for crates under the gateways, where the requirements for a flat line are lower.
FAQ: Frequently Asked Questions
Can I install the MP 20 profile sheet on an old ruberoid roof?
Technically, this is possible, but not recommended without a thorough review. If the old crate is intact, it can be stuffed with a countercrate and a new crate under the profile sheet. However, the ruberoid creates a closed circuit that prevents ventilation. It is better to completely dismantle the old cake or provide a powerful ventilation, otherwise the insulation will rot.
What is the minimum angle of inclination for MP 20?
The minimum angle of inclination for the MP 20 is 12 degrees (or 8 degrees, provided the solid crate and sealing of the joints with silicone). At smaller angles, there is a high risk of water flowing under the horizontal overlaid of sheets.
Do I need to make a solid crate throughout the area?
For MP 20 this is not required if the angle of inclination is more than 15 degrees. A solid crate is required only in the endows (inner corners of the roof), around pipes and attic windows, as well as on eaves overhangs longer than 500 mm.
How to replace the board if it is not on sale?
Alternatively, moisture-resistant plywood or OSB plate with a thickness of 18 mm can be used. However, this will significantly increase the cost of the design. The beam 50x50 mm is also permissible, but the step will have to be calculated again, given its rigidity.