The roof sheathing is a frame that determines the strength, durability and tightness of the entire roof. From the right one sheathing pitch it depends on whether the roof can withstand a snow load, whether it will bend under the weight of a person during repairs, and whether the corrugated sheeting will begin to β€œdrum” in strong winds. But how to determine the optimal distance between boards? Why do metal tiles and ondulin require different approaches? And what mistakes lead to leaks after just a year of operation?

Many home craftsmen mistakenly believe that the sheathing can be installed β€œby eye,” relying on leftover lumber or advice from neighbors. However wrong step is fraught with consequences: from deformation of the roofing to the collapse of the rafter system under extreme loads. In this article we will analyze SNiP standards 2026, we will present ready-made tables for popular materials and show how to calculate the sheathing for a specific region, taking into account wind and snow loads.

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What is roof sheathing and why is it needed?

Lathing is a system of bars or boards laid perpendicular to the rafters. It performs three key functions:

  • πŸ”Ή Support base for roofing materials (corrugated sheeting, metal tiles, ondulin, etc.).
  • πŸ”Ή Load distribution from snow, wind and the weight of people on the rafter system.
  • πŸ”Ή Ventilation gap between the waterproofing and the roof (prevents the formation of condensation).

Without sheathing, even the strongest roofing material will sag under its own weight, and fasteners (screws, nails) will not be able to securely fix the sheets. At the same time sheathing pitch is the distance between centers two adjacent boards, and not between their edges. This nuance often causes installation errors.

Depending on the type of roof, the sheathing is:

  • πŸ“Œ Solid (for soft roofing, roofing felt) - the gap between the boards does not exceed 10 mm.
  • πŸ“Œ Sparse (for corrugated sheeting, metal tiles) - pitch from 200 to 1000 mm.
  • πŸ“Œ Combined (for complex roofs) - alternating solid sections and thin ones.
πŸ“Š What roofing material do you use?
Corrugated sheet
Metal tiles
Ondulin
Soft roof
Other

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SNiP 2026 standards: minimum and maximum steps

There are rules in Russia SNiP II-26-76* (updated edition 2026) and SP 17.13330.2017, which regulate the pitch of the sheathing depending on:

  • πŸ“œ Type of roofing material.
  • πŸ“œ The angle of the slope (the steeper the roof, the less often you can do the sheathing).
  • πŸ“œ Climatic zone (snow and wind loads).

General recommendations for popular materials:

Material Minimum pitch (mm) Maximum pitch (mm) Slope angle
Corrugated sheeting (grades C20-C44) 300 1000 from 8Β°
Metal tiles (Monterrey, Superia) 300 400 from 14Β°
Ondulin (Onduline, Bituwell) 300 600 from 6Β°
Ceramic tiles 320-340 360 from 22Β°
Soft roof (Shinglas, Katepal) Solid β€” from 12Β°

Critical error: for metal tiles with a lathing pitch of more than 400 mm, the manufacturer’s warranty is void! This is due to the risk of deformation of the sheets under point loads (for example, if a person stands on the roof).

⚠️ Attention! In regions with a high snow load (for example, Siberia, the Urals), the pitch of the sheathing under the corrugated sheet is reduced by 20-30% of the norm, even if the slope angle is more than 30°.

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How to calculate the sheathing pitch for your region

The formula for calculating the sheathing pitch takes into account snow (S) and wind (W) loads, as well as weight of roofing material. Main parameters:

  1. Snow load (S) - depends on the climate zone (map in SP 20.13330.2016). For example:
    • Moscow: 180 kg/mΒ²
    • St. Petersburg: 150 kg/mΒ²
    • Novosibirsk: 240 kg/mΒ²
  • Wind load (W) β€” relevant for coastal regions (Kaliningrad, Sochi) and steppe zones.
  • Slope angle (Ξ±) - the steeper the roof, the less snow is retained on it.

    • Simplified calculation algorithm:

    1. Determine the snow load for your region using the map in SP 20.13330.2016.
    2. Multiply it by the slope inclination coefficient (for example, for 30Β° coefficient = 0.8).
    3. Add the weight of the roofing material (corrugated sheeting - 5-7 kg/mΒ², metal tiles - 4-6 kg/mΒ²).
    4. Compare the total load with the load-bearing capacity of the sheathing (for a board 25x100 mm - up to 150 kg/mΒ²).

      5. Determine the snow zone according to SP 20.13330.2016|

      Measure the slope angle |

      Consider the weight of the roofing material|

      Check the load-bearing capacity of the boards (section Γ— wood type)|

      Add a safety margin of 20-30% -->

      Example: for Moscow (S = 180 kg/mΒ²) and a roof with an angle of 25Β°: 180 Γ— 0.8 (angle coefficient) + 6 (metal tile weight) = 150 kg/mΒ².

      With a lathing pitch of 350 mm, the load is distributed over 2 boards, so the actual load per 1 mΒ² of sheathing will be ~75 kg/mΒ², which is safe for a 25Γ—100 mm pine board.

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      Typical mistakes when installing sheathing

      Even experienced roofers make mistakes that shorten the life of the roof. Here are the most common:

      • 🚫 Uneven step β€” leads to β€œwaves” on the corrugated sheeting and leaks at the joints.
      • 🚫 Use of raw wood - after a year the boards are moving, the fasteners are weakening.
      • 🚫 No gaps between the boards of the continuous sheathing (there should be 3-5 mm to compensate for expansion).
      • 🚫 Savings on fasteners - nails instead of screws or insufficient number of fixation points.
      • 🚫 Ignoring the counter-lattice β€” without it, the waterproofing sags, and cold bridges form.
      ⚠️ Attention! If the sheathing is mounted on top of the insulation, the thickness of the boards must be at least 30 mm, otherwise the screws of the roofing material will not hold securely.

      The error with discrepancy between the pitch of the sheathing and the wave of the roofing material. For example, for metal tiles Monterrey with a wave of 350 mm, the lathing must be attached strictly under every second wave, otherwise the sheets will β€œwalk” when there are temperature changes.

      What happens if the sheathing is too thin?

      With a pitch of more than 1000 mm for C20 corrugated sheeting, the roof may sag after the first winter. In places of deflection, microcracks form through which moisture penetrates. In addition, when walking on such a roof, the sheets are deformed and the mounting holes expand, which leads to corrosion.

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      Lathing for different roofing materials

      Each material has its own requirements for the lathing. Let's look at the nuances of the most popular options.

      Profiled sheeting (C20, C21, NS35, etc.)

      For corrugated sheeting, the sheathing pitch depends on stamps (the higher the load-bearing capacity, the less frequently the lathing can be done) and inclination angle:

      • πŸ“ Angle 8-15Β°: pitch 300-400 mm (solid sheathing in valleys).
      • πŸ“ Angle 15-30Β°: step 450-600 mm.
      • πŸ“ Angle >30Β°: step up to 1000 mm (but no more than the distance between the rafters).

      Metal tiles (Monterrey, Superia, Cascade)

      Manufacturers of metal tiles always indicate the recommended step in the instructions. For example:

      • πŸ“ For Monterrey with a wave of 350 mm - a step of 350 mm (fasten under every second wave).
      • πŸ“ For Superia β€” pitch 300-400 mm (depending on the thickness of the metal).

      Ondulin (Onduline, Bituwell)

      Ondulin is a flexible material, so the lathing should be more often than for metal:

      • πŸ“ Angle 5-10Β°: solid lathing or step 300 mm.
      • πŸ“ Angle 10-15Β°: step 450 mm.
      • πŸ“ Angle >15Β°: step up to 600 mm.
      πŸ’‘

      For ondulin, use a lathing made of boards 100-150 mm wide - this will prevent the sheets from sagging in the heat (ondulin softens at +50Β°C).

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      Lathing materials: what to choose

      Traditionally, sheathing is made from wood, but today there are alternatives. Let's compare the options:

      Material Pros Cons Service life
      Edged board (25Γ—100 mm, 50Γ—50 mm) Cheap, easy to install Rots, requires treatment 15-20 years
      Beam (50Γ—50 mm, 60Γ—60 mm) High strength Heavier, more expensive boards 20-25 years
      OSB-3 (18 mm) Does not rot, smooth surface Expensive, difficult to install 30+ years
      Metal profile Doesn't burn, doesn't rot Expensive, cold bridges 50+ years

      For most private homes, the optimal choice is edged board 25Γ—100 mm from pine or spruce, treated with an antiseptic. Important:

      • 🌲 Wood humidity is no more than 20% (otherwise the boards will move).
      • 🌲 The cross-section of the board depends on the pitch of the rafters: if the rafters are located less than 600 mm, take a thicker board (for example, 32Γ—100 mm).
      • 🌲 For continuous sheathing, use moisture-resistant plywood FSF or OSP-3.

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      Step-by-step instructions for installing lathing

      Let's consider a universal algorithm for discharged sheathing under corrugated sheets or metal tiles.

      1. Preparing the rafters:
        • Check the evenness of the rafters using a level (the permissible difference is no more than 2 mm per 1 m).
        • Secure a waterproofing membrane (e.g. Tyvek or Izospan AM) with a sag of 10-20 mm.
      2. Installation of counter-lattice:
        • Nail 30x50 mm bars on top of the waterproofing along the rafters - this will create a ventilation gap.
      3. Marking the sheathing pitch:
        • Mark the first board at the eaves (it should be 10-15 mm thicker than the others to compensate for the deflection).
        • Apply markings taking into account board centers, not the edges!
      4. Fastening boards:
        • Use galvanized nails 70-90 mm or self-tapping screws 50-60 mm.
        • Attach each board in two places to the rafters (closer to the edges).
    5. Geometry check:
      • Measure the diagonals of the slope - the difference should not exceed 20 mm.
    ⚠️ Attention! If the slope length exceeds 6 m, use double boards at the joints of sheets of roofing material to avoid deflections.
    πŸ’‘

    The most common mistake is attaching the sheathing to the rafters β€œoverlay” without a counter-lattice. This leads to wet insulation and rotting of wooden elements.

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    FAQ: Frequently asked questions about sheathing spacing

    Is it possible to make a lathing step of 1 meter for C20 corrugated sheeting?

    No, this exceeds the maximum permissible pitch (600 mm for a tilt angle of 15-30Β°). At a pitch of 1000 mm, the C20 corrugated sheet will sag under the snow load, and the mounting holes will be deformed. An exception is if the slope angle is more than 45Β° and a region with minimal snow load (for example, Krasnodar Territory).

    What lathing pitch is needed for ondulin on a roof with an angle of 10Β°?

    For an angle of 10Β°, the recommended pitch is 450 mm. If you live in a region with high snow loads (for example, Siberia), it is better to reduce the pitch to 300 mm or make a continuous sheathing at the bottom of the slope (the first 1-1.5 m from the eaves).

    Is it possible to use unplaned boards for sheathing?

    Yes, but only if she chamber drying and treated with an antiseptic. Unplaned boards with natural humidity (more than 22%) will begin to warp in a year or two, which will lead to deformation of the roof. The best option is edged board of the 2nd or 3rd grade with a humidity of up to 20%.

    Is it necessary to treat the sheathing with fire protection?

    Definitely! Without treatment, wood rots in 3-5 years, especially in places of contact with metal elements (fasteners, ridge). Use compounds like Senezh Ognebio or Pirilax. They protect against mold, wood-boring beetles and increase fire resistance.

    How to attach the sheathing if the rafters are installed in 1.5 m increments?

    If the rafter pitch is large (more than 1 m), the sheathing needs to be strengthened:

    • Use a board with a cross-section of at least 32x100 mm.
    • Add longitudinal spacers between the rafters (every 500-600 mm).
    • Double the sheathing boards at the joints of sheets of roofing material.

    If the rafters are installed at intervals of more than 1.8 m, it may be necessary continuous lathing from OSB.