Construction of a garage, hangar or shed is impossible without competent calculations loads on trusses - key load-bearing structures that take on the weight of the roof, snow, wind and even seismic activity. Errors at this stage lead to sagging, cracks or collapse of the entire building. But how can an ordinary car owner or self-taught mechanic avoid costly mistakes?

In this article we will look at all types of loads (permanent, temporary, special), we will provide ready-made formulas and coefficients from SP 20.13330.2016, and will also show real examples of calculations for trusses made of profile pipes and I-beams. You will learn how to take into account snow area, roof slope and even the weight of solar panels if you plan to install them. Let's start with the basics - what forces act on a truss and why they cannot be ignored.

1. Types of farm loads: what to consider in 2026

A truss is a rod system that works in compression and tension. Several types of loads act on it simultaneously, which are divided into three categories according to current building regulations:

  • 📌 Constant loads - the weight of the truss itself, the roof, insulation, sheathing. These forces act 24/7 and are calculated with a margin for durability.
  • ❄️ Temporary (variables) - snow, wind, rain, the weight of people during roof repairs. Depends on the climate zone and season.
  • ⚡ Special — seismic activity, blast waves (relevant for industrial zones), emergency situations. Taken into account only in specific projects.

For private buildings (garages, sheds, hangars), the first two categories are usually sufficient. However, if your region is in seismic zones 7-9 points (for example, Kamchatka, Sakhalin, North Caucasus), calculation of special load becomes mandatory.

Important: even in “quiet” regions wind load may exceed snow level. For example, in the steppe zones of southern Russia, wind gusts reach 30 m/s, which is equivalent to pressure ~75 kg/m² on a vertical surface. Now imagine that your farm is not designed for such pressure...

⚠️ Attention: If the roof slope exceeds 30°, the snow load is reduced by 70%, but wind increases 1.5 times due to the sailing effect. This is critical for high hangars!

2. Constant loads: the weight of the truss and roof

Let's start with the simplest thing - static loads. Their calculation is based on specific gravity of materials and the area of the structure. The formula is extremely simple:

Q_post = (Truss weight + Roofing weight + Sheathing weight) × Reliability factor

Where is the reliability coefficient (γ_f) for metal is equal to 1.05, for a tree - 1.1, for concrete - 1.3. Let's look at the example of a truss for a 6x9 m garage with a corrugated roof:

element Material Specific gravity (kg/m²) Area (m²) Total weight (kg)
Truss (profile pipe 60×60×3 mm) Steel — — 180
Profiled sheet C21 Galvanized steel 5.4 54 292
Lathing (board 25×100 mm, pitch 300 mm) Pine 12 54 648
Insulation (mineral wool 100 mm) Basalt wool 10 54 540
Total (with a margin of 1.1) — — — 1802 kg

As you can see, even a “light” roof made of corrugated sheets with insulation provides almost 2 tons load to the farm. And if you plan to install solar panels (weight ~20 kg/m²), add more 1080 kg!

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For trusses longer than 12 meters, be sure to take into account deflection - even with correct load calculations. Use profiles with a section height of at least 1/50 of the span (for example, for 15 m - a 300x300 mm pipe).

3. Snow load: how not to make a mistake with the region

Snow is the main “enemy” of farms in Russia. Its weight depends on snow area (determined from the map in SP 20.13330.2016) and the angle of the roof. Calculation formula:

S = S_g × μ × γ_f

where:


S_g — weight of snow cover per 1 m² (kg/m²),


μ - transition coefficient (depending on the roof angle),


γ_f — reliability factor (1.4 for residential areas, 1.6 for industrial areas).

Let's look at an example for Moscow region (III snow region, S_g = 180 kg/m²) and roofs with a slope of 25°:

  • Coefficient μ for 25° = 0.75 (from the SP table).
  • Reliability factor γ_f = 1.4 (private garage).
  • Roof area = 54 m².

Substitute into the formula:

S = 180 × 0.75 × 1.4 = 189 kg/m²

Total snow load = 189 × 54 = 10,206 kg (!)

This more than 10 tons extra weight in winter! Moreover, in mountainous regions (for example, Krasnoyarsk Territory) S_g reaches 560 kg/m² — farms there are designed with a margin of ×2.

📊 In what region are you building a farm?
Moscow and region
St. Petersburg and Leningrad region
Ural
Siberia
South of Russia
Other
⚠️ Attention: On flat roofs (slope ≤ 12°), snow accumulates unevenly, forming “bags” with a load of up to 2×S_g. For such cases use arched trusses or reinforced sheathing.

4. Wind load: why a truss can “fly away”

Wind affects the farm in two ways:

  1. Frontal pressure - windward side.
  2. Suction (vacuum) - leeward side and eaves overhangs.

The calculation is carried out according to the formula:

W = W_0 × k × c × γ_f

where:


W_0 - standard wind pressure (depending on the area),


k is the coefficient of pressure change with height,


c - aerodynamic coefficient (roof shape),


γ_f is the reliability coefficient (1.4).

For example, let's take Rostov region (II wind region, W_0 = 30 kg/m²), truss height 5 m and gable roof with a slope of 30°:

  • Coefficient k for 5 m = 0.75.
  • Aerodynamic coefficient c for windward slope = +0.8, for leeward = -0.6.

We get:

W_nav = 30 × 0.75 × 0.8 × 1.4 = 25.2 kg/m² (pressure)

W_sub = 30 × 0.75 × (-0.6) × 1.4 = -18.9 kg/m² (suction)

Please note minus sign - this means that the wind is trying to “tear off” the roof. For trusses with a large span (>15 m), such suction can exceed the weight of the structure itself!

What happens if you ignore wind load?

In 2021, in the Krasnodar Territory, a hurricane wind (28 m/s) tore off the roof of a hangar with an area of 500 m² due to incorrect aerodynamic calculations. The trusses were designed only for snow, but not for suction. The repair cost the owner 1.2 million rubles.

5. Practical examples of truss calculations

Now let's combine all the loads and calculate total load on the farm for two scenarios:

Scenario 1: Carport 6x4 m (corrugated sheet, slope 15°)

  • 📍 Region: Kaluga region (III snow, II wind).
  • 🏗️ Truss material: profile pipe 40×40×2 mm.
  • ❄️ Snow: S_g = 180 kg/m², μ = 1 (slope ≤ 25°).
  • 💨 Wind: W_0 = 30 kg/m², k = 0.65 (height 3 m).
Load type Calculation Total (kg)
Constant (40 kg + 5.4×24 + 12×24) × 1.1 528
Snow 180 × 1 × 1.4 × 24 6048
Wind (pressure) 30 × 0.65 × 0.8 × 1.4 × 24 817
Total — 7393 kg

Scenario 2: Hangar 12x20 m (sandwich panels, slope 10°)

  • 📍 Region: Novosibirsk (IV snow, I wind).
  • 🏗️ Truss material: I-beam 16Sh1.
  • ❄️ Snow: S_g = 240 kg/m², μ = 1.
  • 💨 Wind: W_0 = 23 kg/m², k = 1.0 (height 8 m).

For such a flight it is required intermediate support or a truss with a height of ≥ 1/8 span (i.e. ≥ 1.5 m). The total load here will exceed 25,000 kg, so it is better to entrust the calculation to an engineer.

I determined the snow and wind areas according to SP 20.13330.2016|

Measured the exact pitch of the roof (in degrees)|

Took into account the weight of all layers of the roof (including insulation and waterproofing) |

Checked the strength of the support pillars (foundation)|

Added a 20% margin for unexpected loads -->

6. Common mistakes and how to avoid them

Even experienced builders sometimes miss critical points. Here TOP-5 errors, which lead to deformation of trusses:

  • 🔴 Ignoring aerodynamics. On roofs with a slope >30°, the wind creates lift, which is not compensated by the weight of the snow. Solution: use wind cords and anchorage.
  • 🔴 Incorrect truss pitch.
  • 🔴 Saving on material. A profile pipe 20x20 mm can withstand 4 times less than 60x60 mm at the same length.
  • 🔴 Lack of consideration of dynamic loads. For example, vibration from the hangar gate or the movement of equipment inside.
  • 🔴 Independent calculation of complex trusses. For spans >12 m or roofs with broken geometry, you need designer.
⚠️ Attention: If the truss is made of used metal, reduce the design load by 30% - corrosion and microcracks reduce strength.
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For trusses with a span of up to 6 m, simplified formulas can be used. For structures >12 m, calculations in programs are required (SCAD, Lira-SAPR) taking into account the node connections.

7. Programs and calculators for calculations

Manual calculation is suitable for simple structures, but for accuracy it is better to use specialized software:

Program Opportunities Cost Difficulty
SCAD Office 3D modeling, node calculations, wind and seismic loads From 50,000 ₽ ⭐⭐⭐⭐
Lira-SAPR Strength analysis, section optimization, dynamic loads From 35,000 ₽ ⭐⭐⭐⭐
Arkon Calculation of metal structures, drawings, specifications From 25,000 ₽ ⭐⭐⭐
Online calculators (for example, Kalk.Pro) Basic calculations for simple trusses Free ⭐

For a one-time project, you can use free demo versions or order a quote from freelancers (cost from RUB 3,000). The main thing is to check that the report contains:

  • 📄 Force diagrams (compression/tension in each rod).
  • 📊 Calculation for deflection (permissible deflection ≤ 1/200 of the span).
  • 🔧 Recommendations for attaching to the foundation.

FAQ: Frequently asked questions about truss calculations

Can wooden trusses be used for a garage?

Yes, but only for spans up to 6 m and subject to treatment with an antiseptic and fire retardant. For wooden trusses, the reliability factor is increased to 1.2, and the pitch is reduced to 1-1.5 m. Popular sections: timber 100×150 mm or laminated wood.

Example: for a 6x4 m garage in the Moscow region, you will need a truss made of 100x200 mm timber with reinforced units with M12 bolts.

How to take into account the load from solar panels?

Solar panels add 15-25 kg/m² (depending on model). Their weight is added to the constant load. In addition, the panels increase roof windage - wind load must be multiplied by 1.2.

Tip: install panels parallel to the slope, and not perpendicular - this will reduce wind resistance.

Which truss is better: from a profile pipe or an I-beam?

A profile pipe is cheaper and easier to install, but is suitable for spans up to 12 m. The I-beam can withstand heavy loads (up to 50 m), but requires highly qualified welding.

Comparison for a span of 15 m:

  • 🔹 Pipe 100×100×4 mm: weight ~300 kg, maximum load ~5 t.
  • 🔹 I-beam 20B1: weight ~500 kg, maximum load ~12 t.
Is it necessary to coordinate the farm calculation with the supervisory authorities?

For private buildings (garages, sheds) approval is not required if:

  • Area ≤ 50 m².
  • Height ≤ 3 m (to the roof ridge).
  • There is no connection to the house.

For hangars >100 m² or buildings in security zones (for example, next to a gas pipeline) you need project with expertise.

How to test a finished truss for strength?

Visual signs of overload:

  • 🔍 Deflection of rods >1/200 of the span (for example, for 6 m - deflection >3 cm).
  • 🔍 Cracks in welds or near bolted joints.
  • 🔍 Deformation of support units (bearings, beams).

For an accurate diagnosis, use strain gauge (rental cost ~1,500 ₽/day) or contact the non-destructive testing laboratory.