Wind suction protection

Measures for the mechanical fastening of objects or components on the pitched roof are referred to as wind suction protection on the pitched roof in order to protect them against the lifting forces of the wind, the negative wind pressure ( wind suction ). In detail, this article relates to the wind suction protection of small-format covering materials, in particular roof tiles and roofing stones on sloping roof surfaces.

In order to be able to absorb the forces generated by the wind suction , roof tiles and roof tiles are laid in a wind suction- proof system.

description

Wind suction safety system, consisting of roof battens, pan and fastening

A wind suction safety system is understood to mean the interaction of individual components to counteract wind suction . The system consists of a substructure (e.g. roof batten), a covering material (e.g. roof tile ) and a fastening (e.g. storm clip ).

The respective combination is tested in a system test according to DIN EN 14437. The ratio of fastening to brick, tile to roof batten and fastening to batten is assessed on the basis of prescribed failure criteria. The result of the test is on the one hand the force that a fastening can hold against the wind suction . This force is called the design load. On the other hand, there is a total force per m². This results from the number of fastenings and the weight of the roofing itself .

Testing system from Friedrich Ossenberg-Schule GmbH + Co KG to test storm clips according to DIN EN 14437

Every design load relates to this interaction. A storm clip of the same design can be used for different roof tiles, but the design load must be determined anew for each roof tile in the test procedure.

Execution of wind suction protection

Wind suction protection can be achieved in four different designs.

Without attachment.
Every third roof tile is attached.
Every second roof tile is attached.
Each roof tile is attached.

When is no fastening required?

In some sub-areas of a roof area, the wind load can be so low that the weight per unit area of the roofing is sufficient to be able to absorb the loads.

Laying scheme: No pan needs to be attached.

The manufacturers of roof tiles and roof tiles show the corresponding surface weights of the covering for the various roof tiles, which result from the dead weight of a roof tile. This value is called gd, ┴.

The weight per unit area is sufficient for wind suction security if the weight is equal to or, in the best case, greater than the wind load. Since the surface weight is determined vertically, the corresponding roof pitch of the object to be calculated must be taken into account by multiplying cos (DN °) .

The formula for this is: ${\ displaystyle g_ {d, \ alpha} = g_ {d, \ perp} \ cdot \ cos (\ alpha)}$

In this way, the weight per unit area can be compared with the wind loads from the individual roof areas , taking into account the roof pitch , and it can be determined where it is sufficient.

Every third roof tile is attached

The comparison will make it clear that the dead weight is sufficient in only a few or none of the areas. For all other areas, the use of a mechanical fastening must be checked. There are different types of mechanical fastenings with which a roof covering can be secured.

Laying scheme 1: 3. Every third pan is attached.

So far, the wind suction protection by fastening with storm clips has largely proven itself. If no resistance to lifting according to EN 14437 has been determined for a stapling of every third roof tile, the weight of the unsecured roofing may be increased by 30%.

The formula is: . ${\ displaystyle g_ {d, \ alpha; 1: 3} = g_ {d, \ perp} \ cdot \ cos (\ alpha) \ cdot 1 {,} 3}$

This value is compared with the wind loads from the not yet secured roof areas. This makes it clear where the attachment of every third roof tile is sufficient. If a resistance to lifting was determined in a system test for the laying scheme 1: 3 (every third roof tile is attached diagonally), this must be included in the calculation.

Every second roof tile is attached

In the areas in which the fastening of every third roof tile does not yet achieve sufficient resistance, a check is now made to determine which resistance to lifting is offered by the clamping of every second roof tile.

Laying scheme 1: 2. Every second pan is attached.

With the help of the design load, which was determined in a test procedure according to DIN EN 14437, the resistance to lift-off Rd, α; 1: 2 is calculated. This indicates the resistance of the partially fixed roof tiles in KN / m².

Calculation of the lift-off resistance

First, the number of brackets per m² is multiplied by the design load. Then the weight of the roof tiles in KN / m² calculated in the test under 45 ° is adjusted to the actual roof pitch by dividing cosDN by cos45 ° and multiplying by the weight in KN / m². Now both results are added up and give the lift-off resistance in KN / m². ${\ displaystyle R_ {d, \ alpha; 1: 2}}$

The formula is: . ${\ displaystyle R_ {d, \ alpha; 1: 2} = m _ {\ text {fixing}} \ cdot R_ {d, f} + W_ {k, d} \ cdot {\ frac {\ cos (\ alpha) } {\ cos (45 ^ {^ {\ circ}})}}}$

Each roof tile is attached

Depending on the building geometry, layer structure, topographical or geographical location, it is possible that even 1: 2 bracketing is not sufficient in all areas.

Laying scheme 1: 1. Each pan must be attached.

In order to be able to specify a design load for a stapling of each roof tile, the design load determined in the test procedure may be used for the calculation by increasing the number of staples per m² to the same number as roof tiles m². If there is a design load from a separate test in which each roof tile was attached, this must be taken into account.

The formula is: ${\ displaystyle R_ {d, \ alpha; 1: 1} = m _ {\ text {fixing}} \ cdot R_ {d, f} + W_ {k, d} \ cdot {\ frac {\ cos (\ alpha) } {\ cos (45 ^ {^ {\ circ}})}}.}$

The proof of a bracing of each roof tile can now be checked. It should be noted that this is the same formula as with 1: 2 brackets, but a higher value is entered. ${\ displaystyle m _ {\ text {fixing}}}$

Note on wind suction calculation

The processor is constantly faced with the following questions:

Which bracket is required and is it correct?
When and in which roof areas do you need to clamp?
How many brackets do you need?

Providing the relevant property data, the user receives the following results:

the display of all currently assigned storm clips for the selected roof tile
a precise indication of whether and how in which roof areas the brackets must be used
the determination of the strip width
a quantity calculation for the individual roof areas

Various manufacturers of roof coverings offer programs for calculating wind suction to make it easier to determine the appropriate wind suction protection.

literature

German roofing trade - set of rules