Corrugated sheets are one of the most popular materials for roofing, fences and garage cladding due to their strength, durability and affordable price. However, even the highest quality corrugated sheeting will not last long if it is laid on an incorrectly installed sheathing. Sheathing pitch for corrugated sheets - this is a critical parameter on which the load-bearing capacity of the structure, resistance to wind loads and the absence of leaks depend. Errors at this stage lead to sagging sheets, corrosion at fastening points and premature repairs.

In this article we will figure out how to correctly calculate the sheathing pitch for different types of corrugated sheets (roofing, fence, walls), what SNiP and GOST standards regulate this process, and what typical mistakes Beginners allowed. You will find out why for corrugated sheet C8 and NS35 different approaches are required, how the angle of the roof affects the distance between the sheathing boards, and what tools will help simplify installation. And at the end - an FAQ with answers to the most frequently asked questions and useful life hacks from professional roofers.

What is sheathing pitch and why is it important?

The sheathing is a frame made of wooden bars or metal profiles, which serves as the basis for attaching the corrugated sheet. Lathing step - this is the distance between adjacent frame elements, measured along the axes (not along the edges!). This parameter depends on:

  • 🏗️ Roof load-bearing capacity — too large a step will lead to the profiled sheet bending under the snow or the weight of a person during maintenance.
  • 💨 Wind resistance - sparse lathing increases the windage of the sheets, which can lead to the coating being torn off during a storm.
  • 💧 Tightness — an incorrect step can cause deformation of the sheets in the overlap areas, leading to leaks.
  • 🕒 Durability — constant microdeflections due to weak support accelerate corrosion at attachment points.

For example, for corrugated sheet C8 (the most popular for fences) the sheathing pitch is usually 50–60 cm, whereas for roofing NS35 with roof slope 15° a continuous sheathing or a step of no more will be required 30 cm. Ignoring these standards leads to the fact that after 2–3 years the sheets begin to “play” in the wind, and the fastening screws become loose.

⚠️ Attention: If you are installing a profiled sheet on a roof with a slope of less than 10°, the sheathing pitch should be minimal (up to 20 cm) or continuous, regardless of the brand of corrugated sheeting. Otherwise, the water will stagnate in the waves, causing corrosion.

Norms and standards: what SNiP and GOST say

In Russia, the installation of corrugated sheets is regulated by several documents:

  • 📜 SNiP II-26-76 (“Roofs”) - defines the general requirements for the load-bearing capacity of roofing structures.
  • 📜 GOST 24045-2016 (“Bent steel sheet profiles”) - classifies grades of corrugated sheets and their permissible loads.
  • 📜 SP 17.13330.2017 (“Roofs. Updated edition of SNiP”) - clarifies the standards for modern materials.

According to these documents, the lathing pitch depends on:

  1. Profiled sheet brands (its height and metal thickness). For example, S21 withstands greater loads than C8.
  2. Roof angle - the smaller the slope, the more frequent the sheathing should be.
  3. Snow and wind load in the region (determined from maps in SP 20.13330.2016).
  4. Type of construction (roof, fence, wall).

The table below shows minimum permissible sheathing steps for popular brands of corrugated sheets under standard conditions (snow load up to 180 kg/m², wind load - up to 35 kg/m²):

Brand of corrugated sheet Metal thickness, mm Roof angle Max. sheathing pitch, cm Note
C8 0.4–0.5 ≥15° 50–60 For fences - up to 100 cm
S20 0.45–0.7 ≥10° 40–50 With a slope <10° - 30 cm
S21 0.5–0.7 ≥8° 30–40 Popular for garage roofs
NS35 0.6–0.9 ≥5° 20–30 (solid at <5°) For industrial facilities
H75 0.7–1.0 ≥3° 15–25 (solid at <3°) High load-bearing capacity

Please note: if your region belongs to an area with a high snow load (for example, Siberia or the Far East), the lathing pitch should be reduced by 20–30% from the specified values. The same applies to coastal areas with strong winds.

📊 Which professional sheet do you use more often?
C8 (fences, walls)
C21 (garage roofs)
NS35 (industrial facilities)
Another option

How to calculate the pitch of roof sheathing: step-by-step instructions

Calculation of the sheathing pitch for a roofing sheet consists of 5 key steps. Skipping at least one of them may lead to installation errors.

1. Determine the brand of corrugated sheet and its characteristics

For example, you chose corrugated sheet C21-0.5-750. This means:

  • S21 — wave height 21 mm (wall-roof type).
  • 0.5 — metal thickness 0.5 mm.
  • 750 — useful sheet width 750 mm.

This data can be found on the labeling on the packaging or in the product data sheet. If there is no information, ask the seller for a GOST certificate of conformity.

2. Check the angle of the roof

Use a protractor or an online slope calculator. For example:

  • Slope 5–10° - flat roof (garage, shed).
  • Slope 10–30° - standard pitched roof.
  • Slope >30° - steep roof (attic).

3. Check snow and wind loads for your region

Use SP 20.13330.2016 (maps of snow and wind areas). For example, Moscow belongs to III snow region (load 180 kg/m²), and Sochi - to I (80 kg/m²).

4. Use a table or online calculator

Based on the data from points 1–3, select the sheathing pitch according to the table (see section above) or use calculators from corrugated sheet manufacturers (for example, Grand Line or Metall Profile).

5. Adjust the result taking into account additional factors

Reduce the step by 10–20%, if:

  • 🏠 The roof has a complex shape (endova, dormer windows).
  • 🌨️ Region with frequent snowfalls or ice.
  • 🏗️ The corrugated sheet will be used for an insulated roof (additional insulation weight).

☑️ Checklist before installing the sheathing

Done: 0 / 5
⚠️ Attention: If you are installing a profiled sheet on a roof with a slope of less than 8°, be sure to use continuous sheathing from OSB or boards with a gap of no more 10 mm. Otherwise, even a slight deflection will lead to water stagnation and corrosion.

Lathing pitch for fences and walls: key differences

For vertical structures (fences, wall cladding), the requirements for lathing are less stringent than for roofs, but there are some nuances:

  • 📏 Standard step — 50–100 cm for profiled sheet C8–C20.
  • 🌬️ Wind load is the main factor. In open areas (field, coast), the step is reduced to 40–60 cm.
  • 🔩 Fastening - for fences, self-tapping screws with a press washer are used (not roofing ones!), the fastening step is through 1–2 waves.
  • 📐 Fence height - if the height is more 2.5 m, the sheathing is made in two rows (upper and lower beams).

Most often used for fences profiled sheet C8 thick 0.4–0.5 mm. In this case, the optimal lathing pitch is:

  • 🏡 For heights up to 2 m — 60–80 cm.
  • 🏢 For height 2–2.5 m — 50–60 cm.
  • 🌊 For coastal areas - 40–50 cm.

When installing a fence made of corrugated sheets S20 or S21 step can be increased to 100 cm, since these brands have greater rigidity. However, don't forget about vertical racks (supports) - they are installed every 2–3 m, regardless of the sheathing pitch.

💡

For fences over 2.5 m high, use horizontal lathing in two levels (the upper beam is at a height of 1.2 m, the lower one is at the base). This will prevent the sheets from “winding” in strong winds.

Typical mistakes when installing lathing and how to avoid them

Even experienced builders sometimes make mistakes that later lead to problems. Here are the most common:

  1. Ignoring the roof angle

    Many people believe that for profiled sheet C21 one step is always enough 50 cm, but with a slope 5° this will lead to sagging. Solution: use slope-corrected tables (see section above).

  2. Saving on sheathing material

    Beam section 30×30 mm will not withstand the load of snow. Solution: use timber for roofs 50×50 mm or board 25×100 mm.

  3. Uneven sheathing

    If the boards or bars lie in a “wave”, the corrugated sheet will also bend. Solution: check the level every 1–1.5 m.

  4. No ventilation gap

    With an insulated roof, there must be a gap between the sheathing and the corrugated sheet 20–40 mm for air circulation. Solution: use a counter-lattice.

  5. Attaching the corrugated sheet to the sheathing "pull-in"

    The sheets should lie freely, without deformation. Solution: leave a gap 1–2 mm between the screw and the sheet.

Another common mistake is using raw or untreated boards for lathing. Wet wood deforms over time, which leads to bending of the corrugated sheet. Before installation, be sure to dry the timber (humidity no more than 20%) and treat with an antiseptic.

What happens if the sheathing is too thin?

With sparse lathing, the corrugated sheet bends under the weight of snow or when walking on the roof. This leads to:

- wave deformations (sheets become “wavy”),

- loosening of fasteners and leaks,

- accelerated corrosion in places of microcracks.

In the worst case, the coating collapses under heavy snow load.

Tools and materials for lathing installation

For high-quality installation of sheathing under corrugated sheets, you will need:

Basic materials

  • 🪵 timber - section 50×50 mm (roof) or 40×40 mm (fence). For insulated roofs - 50×100 mm.
  • 📏 Edged board - thickness 25–32 mm, width 100–150 mm (for continuous sheathing).
  • 🔩 Fasteners:
    • Wood screws 4.2×70 mm (for attaching the sheathing to the rafters).
    • Self-tapping screws with press washer 4.8×28 mm (for corrugated sheets on fences).
    • Roofing screws 4.8×35 mm with rubber gasket (for roofs).
  • 🛡️ Waterproofing — membrane or film (for roofs).
  • 🧴 Antiseptic - for processing wooden elements.

Tools

  • 🔨 Screwdriver with adjustable tightening torque.
  • 📐 Level (laser or bubble length at least 1 m).
  • 📏 Roulette and a protractor.
  • ✂️ Metal scissors or a jigsaw (for cutting corrugated sheets).
  • 🔧 Drill with a countersink attachment (to recess the screw heads).

To speed up installation you can use pneumatic nail gun (if the sheathing is fastened with nails) or cordless screwdriver with self-tapping strip.

💡

For roofs with a slope of less than 15°, be sure to use anti-condensation film under the sheathing. It prevents the formation of condensation on the inside of the corrugated sheet and extends the service life of the metal.

Practical advice from professionals

Experienced roofers share life hacks that will help you avoid mistakes and save time:

  1. Use a markup template

    Make a wooden template with a length equal to the pitch of the sheathing. This will speed up marking and ensure the same distance between the bars.

  2. Attach the sheathing "staggered"

    The joints of the bars on adjacent rows should not coincide. Shift them to 30–50 cmto avoid weak points.

  3. Check roof geometry before installation

    If the rafters are installed unevenly, the lathing will not save the situation. Use diagonal strings for alignment.

  4. Don't skimp on waterproofing

    Cheap film breaks after 2-3 years. It is better to take a diffusion membrane (for example, Tyvek or Delta).

  5. Consider thermal expansion

    The corrugated sheet “plays” with temperature changes. Leave a gap 5–10 mm between sheets in longitudinal joints.

If you are installing a profiled sheet on an old sheathing, be sure to check its condition:

  • 🔍 Inspect the boards for rot or cracks.
  • 📏 Check the evenness with a level - the deflection is more 5 mm per meter is unacceptable.
  • 🔨 Strengthen weak areas with additional bars or replace damaged areas.

For fences made of corrugated sheets, professionals recommend using metal sheathing from a profile pipe 20×20 mm or 20×40 mm. It is stronger than wood, does not rot and does not require treatment with an antiseptic. However, the cost of such a frame is higher by 30–50%.

FAQ: Frequently asked questions about lathing spacing for corrugated sheets

❓ Is it possible to use a metal profile sheathing instead of a wooden one?

Yes, metal lathing (made from a profile pipe or a hat profile) is even preferable for fences and industrial facilities. It does not rot, does not deform and lasts longer. However, for roofs, wooden sheathing is still more popular due to lower thermal conductivity and ease of installation.

Important: When using metal, be sure to treat the cut areas with an anti-corrosion compound (for example, Tsinkor-Auto).

❓ What sheathing pitch is needed for a C8 profiled sheet on a garage roof with a 10° slope?

For corrugated sheet C8 thick 0.5 mm on a slope 10° maximum sheathing pitch - 30 cm. If the slope is less (for example, 5–8°), continuous sheathing or step required 20 cm.

Also take into account the snow load: for the Moscow region (III district) it is better to reduce the step to 25 cm.

❓ Is it necessary to treat wooden sheathing with a fire retardant compound?

Fire protection is not mandatory according to SNiP for private houses, but is recommended for:

  • 🏢 Industrial facilities.
  • 🏠 Houses with stove heating or fireplaces.
  • 🌲 Regions with high fire danger (forest zones).

For processing, use class compounds G1 (for example, Neomid 450 or Pirilax).

❓ Is it possible to attach a corrugated sheet to the sheathing with nails instead of self-tapping screws?

Technically possible, but highly not recommended. Nails:

  • 🔨 Over time, they become loose due to vibrations (wind load).
  • 💧 The holes are not sealed, which leads to leaks.
  • 🔩 They can damage the polymer coating of the profiled sheet when hammered.

An exception is temporary structures (for example, a canopy in a country house). In this case, use galvanized nails with a wide head and a rubber gasket.

❓ How to calculate the amount of timber for sheathing?

Calculation formula:

Number of bars = (Ramp length / Sheathing pitch) + 1

Total length of timber = Number of timber × Length of slope

Example: slope length 6 m, sheathing pitch 40 cm (0.4 m).

Quantity = (6 / 0.4) + 1 = 15 + 1 = 16 bars

Total length = 16 × 6 = 96 m

Add 10% for trims and joints.