A canopy made of corrugated sheets is a practical solution for protecting a car, garden equipment or recreation area from rain and sun. But the durability of the structure directly depends on the quality battens, on which the roofing material is attached. Incorrect pitch or poor-quality material leads to sagging sheets, accumulation of condensation and even collapse of the roof under snow load.

In this article we will look at how to choose optimal lathing pitch depending on the brand of corrugated sheeting, climatic conditions and the angle of inclination of the canopy. Let's consider the pros and cons of wooden and metal structures, as well as typical mistakes made during installation. We will pay special attention to calculations for regions with high snow loads - this will help avoid roof deformation in winter.

Why do you need lathing for corrugated sheeting on a canopy?

The sheathing performs three key functions:

  • 🔹 Load distribution — evenly transfers the weight of corrugated sheeting, snow and wind to the load-bearing elements of the frame.
  • 🔹 Ventilation — creates a gap between the roofing material and the waterproofing, preventing the accumulation of condensation.
  • 🔹 Fastening sheets — provides reliable fixation of corrugated sheeting with self-tapping screws without the risk of deflection.

Without lathing, even thick corrugated sheets grade H60 Over time, it becomes deformed under the weight of snow, especially if the angle of the canopy is less than 15°. In regions with frequent precipitation (for example, the Leningrad region or the Urals), this leads to sagging of the roof after 2-3 winters. At the same time metal lathing can withstand 30-40% greater load than wooden lathing of the same section, but requires anti-corrosion treatment.

One more nuance - thermal expansion corrugated sheets In summer the sheets heat up to +70°C, and in winter they cool down to -30°C. The sheathing compensates for these deformations, preventing the appearance of waves on the roof. If the step between the boards or profiles is too large, the sheets begin to “play”, which leads to leaks in the places where the screws are attached.

📊 What lathing material do you use?
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Metal (profile, channel)
Combined (wood + metal)
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Types of lathing: wooden vs metal

The choice of material depends on the budget, climatic conditions and service life of the canopy. Let's look at the pros and cons of each option.

Parameter Wooden sheathing Metal sheathing
Service life 10-15 years (when treated with an antiseptic) 25+ years (with anti-corrosion coating)
Cost Low (from 150 rub/m²) High (from 400 rub/m²)
Installation Simple, no welding required More difficult, you need metal working skills
Load Up to 200 kg/m² (depending on the type of wood) Up to 500 kg/m² (for profile 40×40 mm)
Moisture resistance Low (requires waterproofing) High (if properly processed)

Wooden sheathing is suitable for lightweight sheds in temperate regions. Optimal breeds - pine or larch, since they are less susceptible to rotting. The boards must be dry (humidity no more than 18%) and treated deep penetration antiseptic (for example, Senezh Ultra or Pinotex Classic). The thickness of the boards is at least 25 mm, width is 100-150 mm.

Metal sheathing made of profile pipe (40×20 mm or 40×40 mm) or channel withstands significant loads and does not require annual maintenance. However, its weight increases the load on the support pillars, so the canopy frame must be strengthened. To protect against corrosion, use galvanized or powder-coated profiles. Be sure to prime and paint welds.

⚠️ Attention: If the canopy is located near the sea or in an industrial area, the metal sheathing will last 2-3 times less due to the aggressive environment. In such cases, choose aluminum profiles or stainless steel.

Calculation of sheathing pitch: formulas and practical tips

The sheathing pitch is the distance between the centers of two adjacent boards or profiles. It depends on:

  • 📏 Brands of corrugated sheets (metal thickness, wave height).
  • ⛱️ Canopy tilt angle (the smaller the angle, the faster the step).
  • ❄️ Snow load in the region (see SP 20.13330.2016).
  • 💨 Wind load (relevant for open areas).

Basic pitch recommendations for popular brands of corrugated sheeting:

  • 🔹 S8, S10, S20 (thickness 0.4-0.5 mm) - step 30-40 cm with a slope of 15°.
  • 🔹 S21, NS35 (thickness 0.5-0.7 mm) - step 50-60 cm with a slope of 10°.
  • 🔹 H60, H75 (thickness 0.7-0.9 mm) - step up to 1 m with a slope of 8°.

For an accurate calculation, use the formula:

Lathing pitch (cm) = (Permissible load of corrugated sheeting (kg/m²) × sin(tilt angle)) / (Snow load (kg/m²) × 1.2)

Where 1.2 — safety factor. For example, for corrugated sheet H60 (load 300 kg/m²) in Moscow (snow load 180 kg/m²) with a slope of 10°:

Step = (300 × sin(10°)) / (180 × 1.2) ≈ 48 cm

If the canopy is located in a windy region (for example, steppe zones or the coast), the step is reduced by 20-30%. For open areas it is also recommended to use continuous sheathing along the edges of the roof (first and last 50 cm) - this will prevent the sheets from falling off during gusts of wind.

Check the evenness of the canopy frame with a level|Calculate the pitch taking into account the snow load|Treat the wooden elements with an antiseptic|Prepare a waterproofing membrane (if necessary)|Drill holes in the metal profiles in advance (if fastened with bolts)-->

Step-by-step instructions for installing lathing

Work begins after assembling the canopy frame and installing the rafters. Procedure:

  1. Preparing the base. Clear the rafters of debris and check their levelness. If necessary, place gaskets made of roofing felt or EPPS for alignment.
  2. Laying waterproofing. If the canopy is closed (with sides), use diffusion membrane (for example, Tyvek or Yutawek). For open structures, processing of wooden elements is sufficient hydrophobic composition.
  3. Attaching the sheathing.
    • 🔨 For wooden sheathing, use wood screws (length 50-70 mm) or screw threaded nails. The fastening step is 30-40 cm.
    • 🔧 Suitable for metal sheathing bolts M8-M10 with growers or screws for metal with a press washer.
  • Plane control. After installation, check the evenness of the sheathing string or laser level. The permissible deviation is no more than 2 mm per 1 m of length.

    • When installing wooden sheathing, leave gap 2-3 mm between boards to compensate for wood expansion due to humidity. Attach metal profiles tightly, but avoid rigid fixation - use oval holes under bolts for free movement during temperature deformations.

    ⚠️ Attention: If the canopy is adjacent to a house or other building, attach the first sheathing board at a distance of 5-10 cm from the wall. This will prevent moisture accumulation and mold formation on the facade.
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    To speed up installation, use a template from a cut board - it will help maintain the same spacing between the sheathing elements.

    Common mistakes and how to avoid them

    Even experienced craftsmen make mistakes when installing sheathing, which lead to leaks or deformation of the roof. Let's look at the most common ones:

    • 🚫 Ignoring the angle of inclination. With a slope of less than 8°, the sheathing pitch should be minimal (30-40 cm), otherwise water will stagnate in the waves of corrugated sheeting.
    • 🚫 Saving on material. Using boards less than 25 mm thick or a profile thinner than 40×20 mm leads to sagging under the snow.
    • 🚫 No ventilation gap. If the waterproofing is laid close to the corrugated sheet, condensation destroys the sheathing in 3-5 years.
    • 🚫 Uneven frame. Rafter height differences of more than 5 mm lead to deformation of the sheets during fastening.

    Another critical error - fastening corrugated sheeting to the sheathing without sealing washers. This leads to:

    • 💧 Leaks in places where screws are screwed in.
    • 🔊 Creaks and rattling of sheets in the wind.
    • 🛠️ Corrosion of metal around holes.

    To seal, use self-tapping screws with EPDM gasket (for example, Klopper or SFS). Tighten them with a force of 15-20 Nm - insufficient force will lead to leaks, and excessive force will damage the gasket.

    What to do if the sheathing is already deformed?

    If boards or profiles sag under the weight of snow, temporarily reinforce them with additional supports (for example, telescopic stands). In the spring, dismantle the corrugated sheeting, replace damaged sheathing elements and reduce the spacing between them by 30-40%. For metal sheathing you can use reinforcing pads made of sheet steel 3-4 mm thick, welded to sagging areas.

    Sheathing for canopies in regions with high loads

    In the northern regions (Murmansk region, Siberia) or mountainous areas (Caucasus, Altai), the snow load exceeds 300 kg/m². In such cases, standard recommendations for lathing spacing are not suitable. Here's what to consider:

    • 🏔️ Increase the thickness of the corrugated sheet up to 0.8-1 mm (grades H75 or H114).
    • 🏗️ Use double sheathing: the first layer is sparse (step 50-60 cm), the second is solid from boards 25x100 mm.
    • ❄️ Install snow guards every 1.5-2 m to avoid avalanches of snow.
    • 🔩 Strengthen the fastening - use self-tapping screws 80-100 mm long in increments of 20-25 cm.

    To calculate the exact load, use data from SP 20.13330.2016 "Loads and impacts". For example, in Norilsk snow load reaches 560 kg/m², and in Sochi - only 70 kg/m². If the canopy is located in an open area (field, hill), the wind load is increased by 40%.

    For metal sheathing in such conditions it is recommended:

    • 🔹Use profile 60×40 mm with a wall thickness of 2 mm.
    • 🔹 Attach profiles to rafters M12 bolts with nuts and groovers.
    • 🔹 Treat all welds zinc spray (for example, Zinga).
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    In regions with high loads, the sheathing pitch for H60 corrugated sheets should not exceed 40 cm, even if the angle of inclination is more than 15°.

    Care and repair of sheathing: extending service life

    Wood sheathing requires annual inspection and treatment. Signs that it's time to take action:

    • 🔍 Darkening of wood (beginning of rotting).
    • 🐜 Presence of rotten areas or traces of wood-boring beetles.
    • 💦 Blistering of paint or varnish (moisture ingress).

    For repair:

    1. Remove damaged areas chisel or cycles.
    2. Treat bare wood wood bleach (for example, Neomid 500).
    3. Apply 2 coats antiseptic with an interval of 4 hours.
    4. After drying, cover acrylic paint for outdoor work.

    Metal sheathing lasts longer, but also requires maintenance:

    • 🔹 Once every 2 years, clean the profiles from rust wire brush or sandblaster.
    • 🔹 Cover damaged areas primer GF-021 and hammer paint.
    • 🔹 Check the mounting bolts - if they are corroded, replace them with galvanized.

    If the shed is used to store equipment or a car, once every 5 years it is recommended complete revision of the sheathing:

    1. Remove 2-3 sheets of corrugated sheets for visual inspection.
    2. Check the integrity of the waterproofing and ventilation gaps.
    3. If necessary, reinforce the sheathing with additional profiles.
    ⚠️ Attention: If condensation appears on the inside of the corrugated sheet, this is a sign of poor ventilation. Increase the gap between the sheathing and the roofing material to 3-5 cm or install ventilation grilles at the ends of the canopy.

    FAQ: Frequently asked questions about lathing under corrugated sheets

    Can sheathing be made from plywood or OSB?

    For awnings not recommended use plywood or OSB as sheathing. These materials cannot withstand point loads from self-tapping screws and, over time, delaminate under the weight of the corrugated sheeting. Exception - moisture resistant plywood FSF 18-22 mm thick for continuous sheathing under a soft roof, but it will last no more than 7-10 years.

    If you need to save money, it is better to use unedged board (25×150 mm), cleared of bark and treated with an antiseptic. It is cheaper than planed wood, but with proper preparation it will last no less.

    What lathing pitch is needed for C21 corrugated sheeting on a canopy with a 5° slope?

    For corrugated sheet C21 (thickness 0.5-0.7 mm) with a slope of 5°, the sheathing pitch should be no more than 30 cm. This is due to:

    • Low load-bearing capacity of grade C21 (maximum load - 150 kg/m²).
    • Risk of accumulation of snow and water due to the small angle of inclination.

    If the canopy is located in a region with a snow load of more than 120 kg/m² (for example, the Moscow region), reduce the pitch to 20-25 cm or use thicker corrugated sheeting (NS35 or H60).

    Is waterproofing needed under corrugated sheeting on an open shed?

    For open canopies (without side walls) a waterproofing membrane is not required, but is recommended:

    • 🔹 If the sheathing is wooden, the membrane will protect the boards from condensation that forms on the inside of the corrugated board during temperature changes.
    • 🔹 If the canopy is adjacent to the house, waterproofing will prevent moisture from getting on the wall.

    Instead of a membrane you can use diffusion film (for example, Yutacon) or process the sheathing hydrophobic composition (for example, Belinka Impregnant).

    How to attach the sheathing to the metal frame of the canopy?

    To attach the sheathing to metal rafters, use:

    • 🔹 Self-tapping screws for metal (length 25-35 mm) - for wooden sheathing.
    • 🔹 Bolts M8-M10 with growers - for metal sheathing.
    • 🔹 Aluminum rivets (diameter 4-5 mm) - for thin-walled profiles.

    When attaching wooden boards to metal, be sure to use galvanized hardware and rubber gasketsto avoid corrosion at points of contact between different materials.

    If the rafters are made of profile pipe, pre-drill holes in the metal 0.5 mm larger than the diameter of the bolt - this compensates for thermal expansion.

    How to strengthen the sheathing if the canopy is already sagging under the snow?

    If the sheathing is deformed, but the canopy frame is intact, follow these steps:

    1. Install temporary supports from timber 100×100 mm or telescopic racks.
    2. Remove the corrugated sheeting and inspect the sheathing. Remove rotten boards or bent profiles.
    3. Strengthen the structure:
      • 🔹 For wooden sheathing - add additional boards between the existing ones, reducing the step by 2 times.
      • 🔹 For metal sheathing - weld corners 40×40 mm or sheet steel trims.
  • Increase the angle of the canopy to 10-15° (if the frame design allows it).
  • Install snow guards and arrange for regular roof cleaning in winter.

    • If the deformation is severe, consider replacing the corrugated sheet with polycarbonate — it is lighter and better tolerates point loads.