EN 1991-1-4: Wind on Free-Standing Walls and Parapets - Net Wind Pressure per Zone (Section 7.4)

About this Free-Standing Wall and Parapet Wind Calculator

This calculator gives the net wind pressure on each zone of a free-standing wall or parapet to EN 1991-1-4 Section 7.4.1, using the recommended values with no National Annex. The peak velocity pressure is worked at the top of the wall, the wall is divided into zones A, B, C and D from its free end (Figure 7.19), and the net pressure coefficients of Table 7.9 are interpolated on the length to height ratio, the return corner length and the solidity.

• Boundary wall designer sizes masonry, concrete and panel fence walls, and their footings, for the high end-zone pressures.
• Roof parapet engineer gets the net pressure on parapets for the parapet itself and its connection back to the roof structure.
• Acoustic and screen wall engineer checks noise walls and screens, using the solidity ratio for walls that are not fully solid.

Each zone's extent from the free end, net coefficient and net pressure are summarised together, with a check that the solidity is within Table 7.9. It is an engineering-grade calculation you can duplicate and adapt in a CalcTree workspace.

More info on Free-Standing Wall and Parapet Wind

Reference height

The reference height is the top of the wall, the height of its base above the ground plus the wall height. This lets the same page cover a wall standing on the ground and a parapet on a roof. The peak velocity pressure is worked there from Section 4.

Zones from the free end

The zones are set out from the free end of the wall (Figure 7.19): A over a short end strip, then B, C and D in turn along the wall, each defined as a multiple of the wall height. On a wall too short to reach a zone, that zone does not occur and carries no pressure. A wall free at both ends has the same zones from each end.

Table 7.9 and interpolation

Table 7.9 gives the net pressure coefficients for a solid wall without return corners at three length to height ratios, and the page interpolates linearly between them. A return corner as long as the wall is high gives its own row, with linear interpolation on shorter return corners. For a wall that is not fully solid, the coefficients are interpolated on the solidity ratio down to the lowest solidity the table covers.

Net pressure

The net pressure on each zone is the peak velocity pressure times its net pressure coefficient (Section 5.2). It acts across the wall, on its windward face and away from its leeward face together, so it is the load for the wall's bending and its support.

Common Calculation Errors to Avoid

• Using one coefficient for the whole wall Zone A at the free end carries the highest net pressure. Designing the full length for the zone D value understates the load at the end.
• Ignoring return corners A return corner changes the coefficients near the free end. Leaving it out, or treating a short return as a full one, gives the wrong end-zone pressure.
• Applying Table 7.9 to an open fence or screen Below the lowest solidity in the table the wall is a plane lattice under Section 7.11, which this page does not cover.
• Leaving out the base height of a parapet The reference height is the top of the parapet above the ground. Enter the base height so the peak velocity pressure is taken at the right level.
• Forgetting shelter is not applied Walls behind other walls may take a shelter factor under Section 7.4.2. This page does not apply it, so results for a sheltered wall are conservative.

FAQs

What is a free end?

The end of a wall that is not tied into a return or another wall. Flow round the free end causes the highest net pressures, which is why zone A sits there.

How does a return corner change the result?

A return corner turning back from the free end changes the coefficients near that end, lowering zone A. Table 7.9 gives a row for a return corner as long as the wall is high, and the page interpolates linearly for shorter ones.

Can I use this for a roof parapet?

Yes. Enter the height of the parapet base above the ground and the parapet height. The reference height becomes the top of the parapet, and the zones are set out from its free end.

What if the wall has gaps?

Enter the solidity ratio, the solid area over the overall area. The page interpolates Table 7.9 down to the lowest solidity it covers. Below that, treat the wall as a plane lattice under Section 7.11.

Is the shelter factor included?

No. The shelter factor for walls behind other walls (Section 7.4.2, Figure 7.20) is not applied here.