Lathing distance for corrugated sheeting: how to calculate the pitch for a roof without leaks and deflections

Corrugated sheeting is one of the most popular roofing materials for garages, outbuildings and private homes due to its strength, durability and affordable price. However, even the highest quality corrugated sheet will not save the roof from leaks or deformations if it is not properly installed underneath. sheathing. The main parameter that determines the reliability of the entire structure is distance between sheathing boards. Errors at this stage lead to sheets bending under the snow, creaking in the wind and a reduction in the service life of the roof by 2-3 times.

In this article we will look at how calculate the sheathing pitch for corrugated sheeting depending on the angle of inclination of the roof, brand of material and climatic conditions. You will find out what regulations govern SNiP II-26-76 (updated edition 2026), how to avoid common mistakes during installation and what to do if the roof is already sagging. And for those who plan the work on their own, we have prepared step-by-step instructions with checklists and tables with ready-made pitch values for different types of profiled sheets.

Warning: if you are installing corrugated sheeting on a roof with a slope of less than 8°, the sheathing must be solid (from OSB or plywood) - otherwise leaks at the joints of the sheets are guaranteed!

1. Why is the sheathing pitch critical for corrugated sheeting?

Sheathing for corrugated sheets performs three key functions:

• 🔹 Load distribution — evenly transfers the weight of snow, wind and the material itself to the rafter system.
• 🔹 Ventilation — creates a gap between the corrugated sheet and waterproofing, preventing condensation and rotting of wooden elements.
• 🔹 Fastening sheets — provides rigid fixation of the corrugated sheet in places where screws are screwed in.

If the sheathing pitch overpriced, the corrugated sheet bends under the snow, and the fastenings become loose. If understated - the consumption of materials and the weight of the structure increases unnecessarily. The optimal distance depends on:

• 📏 Roof angle (the lower the slope, the more frequent the sheathing).
• 🏗️ Brands of corrugated sheets (metal thickness and wave height).
• ❄️ Snow and wind load in the region (by SP 20.13330.2016).

Critical mistake: on roofs with a slope of 5–8°, the sheathing is installed in increments of 30–40 cm, although such corners require a solid base or a spacing of no more than 15 cm. This leads to leaks at the joints of the sheets after 1–2 winters.

2. Sheathing pitch standards according to SNiP and grades of corrugated sheets

The main document regulating the installation of roofs made of corrugated sheets is SNiP II-26-76* (updated edition 2026). According to him, the sheathing pitch depends on:

1. Wave heights of corrugated sheets (h).
2. Metal thickness (t).
3. Roof angle (α).

Below is a table with recommended steps for popular brands of corrugated sheets (the data is relevant for central Russia, where the snow load is up to 180 kg/m²):

Brand of corrugated sheet	Wave height (mm)	Metal thickness (mm)	Roof slope	Max. sheathing pitch (cm)
S-8	8	0.4–0.5	≥15°	30–40
NS-20	20	0.45–0.7	≥10°	30–50
N-60	60	0.7–0.9	≥8°	50–100
N-75	75	0.8–1.0	≥6°	100–150
MP-35	35	0.5–0.8	≥12°	40–60

⚠️ Attention: For regions with high snow load (Urals, Siberia, Far East), the sheathing pitch is reduced by 20–30%. For example, for NS-20 with a slope of 10°, instead of 50 cm, make 35–40 cm.

3. How to calculate the sheathing pitch yourself

To accurately calculate the sheathing pitch, use the formula:

Step (cm) = (Ramp length (m) × 100) / (Number of sheets along the width of the ramp + 1)

But this method gives maximum permissible step. To take into account the loads, adjust the result according to the table:

Snow load (kg/m²)	Step reduction factor
Up to 120	1.0 (step unchanged)
120–180	0.8
180–240	0.6
Over 240	0.5 (solid sheathing)

Example: The length of the slope is 6 m, we use corrugated sheets NS-35 (step according to the table - 50 cm), snow load - 200 kg/m².

1. Basic pitch: (6 × 100) / (Number of sheets + 1) ≈ 50 cm.
2. Load adjustment: 50 cm × 0.6 = 30 cm.

How to find out the snow load in your region?

Open SP 20.13330.2016 (updated version) or use the online map on the Hydrometeorological Center website. For Moscow and the region, the load is 180 kg/m², for Krasnoyarsk - 320 kg/m².

4. Typical mistakes when installing sheathing

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

• 🚫 Uneven sheathing — differences in height of more than 2 mm per 1 m lead to “waves” on the corrugated sheet.
• 🚫 Savings on boards — the use of damp or thin (less than 25 mm) bars leads to their deformation.
• 🚫 No gaps — there should be a gap of 2–3 mm between the ends of the boards to compensate for the expansion of the wood.
• 🚫 Ignoring the counter-lattice — without it, condensation accumulates on the waterproofing.

⚠️ Attention: If you attach corrugated sheeting to the sheathing nails instead of self-tapping screws, the step between the boards should be reduced by 30% - nails do not provide rigid fixation under wind loads.

Make sure that all boards are treated with an antiseptic |

Check the evenness of the sheathing with a level (tolerance - 2 mm/m) |

Leave 2–3 mm gaps between the ends of the boards|

Install a counter-lattice for ventilation|

Check the step according to the table taking into account the loads

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5. Lathing for different types of roofs

The sheathing pitch varies not only according to the slope, but also according to roof structures:

🏠 Shed roof (slope 5–15°)

Requires continuous sheathing or a step of no more than 20 cm due to high snow load. Exception - corrugated sheets N-60 and higher: a step of 30–40 cm is allowed for it with a slope of 10°.

🏡 Gable roof (slope 15–45°)

The optimal step is 30–60 cm, depending on the brand of profiled sheet. On the ridge and valley, the step is reduced to 10–15 cm for rigidity.

⛪ Complex roofs (hip, mansard)

At the junctions of the slopes (valleys) sheathing is made solid to a width of 30–50 cm. In other areas, the pitch is calculated using standard tables.

6. Materials for sheathing: what to choose

For sheathing under corrugated sheets use:

• 🌲 Edged board (25×100 mm or 32×100 mm) - the best option in terms of price and strength.
• 🪵 timber (50×50 mm) - suitable for pitches over 60 cm (for example, under N-75).
• 📦 OSB or plywood (thickness 12–18 mm) - for continuous sheathing on flat roofs.

⚠️ Attention: Do not use unedged board — its uneven edges lead to distortions of the profiled sheet. Also avoid materials with humidity above 20%: when drying, the boards “lead” and the roof becomes deformed.

To extend the service life of the sheathing:

1. Treat all wooden elements antiseptic (for example, Senezh Ultra).
2. In places adjacent to metal elements (pipes, snow guards), use waterproofing tapes.
3. To attach the sheathing to the rafters, use rough nails (length 70–90 mm) or self-tapping screws.

7. How to correct sheathing errors if the roof is already installed

If after installing the corrugated sheeting you notice sagging or creaking, do not rush to redo the entire roof. Depending on the problem:

• 🔧 Deflection of sheets under snow → Install additional sheathing boards on top of existing ones in problem areas.
• 💧 Leaks at joints → Check the tightness of the seals and add sealant tape under overlaps.
• 🌬️ Creak in the wind → Strengthen the fastening of the corrugated sheet (add screws to the wave) and check the rigidity of the rafters.

For a temporary solution (for example, before winter), you can install snow guards - they will reduce the load on the sheathing. But this does not eliminate the need for rework in the spring.

FAQ: Frequently asked questions about the sheathing pitch under corrugated sheeting

Is it possible to make a sheathing step of 1 meter for N-60 corrugated sheeting?

Yes, but only if the following conditions are met:

• Roof slope ≥15°.
• Snow load ≤180 kg/m².
• Corrugated sheet thickness ≥0.7 mm.

For regions with high loads (for example, mountainous areas), the step is reduced to 60–80 cm.

Is a vapor barrier under the sheathing necessary if the roof is cold?

For cold roofs (without insulation) vapor barrier is not required. A waterproofing membrane laid with a ventilated gap of 2–3 cm is sufficient.

How to attach the sheathing to the rafters: with nails or self-tapping screws?

Both options are acceptable, but:

• Nails (70–90 mm) are cheaper, but become loose over time.
• Self-tapping screws (for wood, 50–60 mm) more reliable, especially in regions with strong winds.

For lathing under heavy corrugated sheeting (for example, N-114) use reinforced fastenings - self-tapping screws with hexagonal heads.

Is it possible to use metal sheathing under corrugated sheeting?

Yes, but only in industrial construction. For private houses, metal sheathing is not practical due to:

• High cost (3-4 times more expensive than wood).
• Difficulty in installation (requires welding or specialized fasteners).
• Risk of corrosion at points of contact with corrugated sheets.

What sheathing pitch is needed for corrugated sheeting on a garage with a 5° slope?

With such a small slope, the sheathing should be solid (from OSB or boards with a gap of 1–2 cm) or in increments of no more 10–15 cm. Use corrugated sheeting with a wave height of 44 mm (for example, NS-44 or N-60).

⚠️ Important: be sure to use on flat roofs joint sealant (for example, Tytan Professional).