EN 1991-1-4: Wind Pressure on Monopitch Roofs (Section 7.2.4)

About this Monopitch Roof Wind Pressure Calculator

This calculator gives the net wind pressure on each zone of a monopitch roof to EN 1991-1-4 Section 7.2.4, for wind blowing onto the low eave, using the recommended values with no National Annex. It divides the roof into zones F, G and H (Figure 7.7), interpolates the external pressure coefficients of Table 7.3a on the roof pitch, and reports a pressure load case and a suction load case for every zone.

• Designer of lean-to and skillion roofs gets zone pressures for rafters, purlins and roof sheeting on carports, verandahs and lean-to extensions.
• Industrial building engineer checks single-slope sheds and canopied buildings where the low eave faces the prevailing wind.
• Reviewer sees the Table 7.3a interpolation and the internal pressure pairing laid out for each load case.

Each zone's pressure and suction are shown side by side with the pitch check. It is an engineering-grade calculation you can duplicate and adapt in a CalcTree workspace.

More info on Monopitch Roof Wind Pressure

Reference height and peak velocity pressure

The reference height of a monopitch roof is the height of the building to the high eave. The peak velocity pressure is worked at that height from the basic wind velocity, terrain category, orography factor, turbulence factor and air density through Section 4, with the basic velocity pressure (Eq. 4.10) reported alongside.

Zones from Figure 7.7

The zones are set out from the upwind, low eave using the length e, the smaller of the crosswind dimension and twice the height. Zone F sits at each upwind corner and G between them, both e/10 deep, and H covers the rest of the roof.

Table 7.3a coefficients

Table 7.3a gives a suction and a pressure coefficient for most pitches. The page interpolates linearly between the tabulated pitches, suction with suction and pressure with pressure. Above 45° the table gives a pressure value only, so the suction case is held at zero there, and a pitch outside the table is held at the nearest row with a failed pitch check.

Two load cases

Coefficients of opposite sign are not mixed. Load case 1 takes every zone's pressure coefficient with the negative internal coefficient, and load case 2 every zone's suction coefficient with the positive one, because each pairing gives the larger net value (Section 5.2).

Common Calculation Errors to Avoid

• Checking only wind onto the low eave This page covers wind onto the low eave. Wind onto the high eave and wind along the eaves (Table 7.3b) give different zones and larger suctions and must be checked separately.
• Taking the reference height at the low eave Section 7.2.4 uses the height to the high eave. The low eave height understates the peak velocity pressure.
• Mixing pressure and suction across zones Within one load case all zones take the same sign of coefficient. Combining a pressure value in one zone with a suction value in another is not a code load case.
• Using c_pe,10 for fixings The coefficients are for loaded areas of 10 m² or more. Cladding and fixings with smaller loaded areas need c_pe,1.
• Treating a very shallow roof as monopitch Below 5° the roof is treated as flat under Section 7.2.3.

FAQs

Which wind direction does the page cover?

Wind blowing onto the low eave, the θ = 0° case of Table 7.3a. Wind onto the high eave and along the eaves use other columns and Table 7.3b, and need a separate check.

Why are there only two load cases?

A monopitch roof has a single slope, so the code's suction and pressure values give one all-suction case and one all-pressure case. Each is paired with the internal coefficient that makes the net value larger.

What pitch range is covered?

Pitches from 5° to 75°. A pitch outside that range is held at the nearest table row and the pitch check fails.

Where is the reference height taken?

At the height of the building to the high eave, or at the minimum height for the terrain category if that is higher.

Can I change the turbulence factor and air density?

Yes. Both are inputs on this page, so values from the National Annex for the country of use can replace the recommended values.