Designing the Right Single Ply Roofing System

Fastener Withdrawal Resistance & Resistance To Wind Load

Fastener withdrawal resistance tests are recommended on certain refurbishment projects to determine the suitability of the roof deck.
The withdrawal resistance test may be conducted by an independent laboratory or the fastener manufacturer or their designated representative. The results of the pullout tests must be designated on a roof plan to indicate the areas at which the tests were conducted and forwarded to Icopal for review.

On refurbishment projects, a core cutter should be used to remove existing roofing material prior to conducting the withdrawal resistance test (even if the existing roofing membrane is specified to remain).
Existing roofing materials will contribute to a higher, misleading pullout value.

The withdrawal resistance tests should be carried out in various locations of the roof deck, such as:

  • Roof corners
  • At perimeter areas (minimum of 3 each).
  • Field of the roof (with at least 2 tests conducted at the low areas of the roof deck).

Resistance to wind load

The affect of wind upon a single ply roof covering should be determined at an early stage. Wind loads are determined by completion of a calculation as recommended in EN 1991.

The calculation will take the following factors into account:

  • Geographical Location (eg, coastal, urban, rural)
  • Site topography
  • Building height
  • Building design
  • Large openings
  • Method of attachment

This calculation must be carried out early on in the design process.

Completion of the membrane wind uplift calculation will confirm the fasteners centres / spacings for the following roof zones:

  • Corners / Perimeter
  • Field Area or central zone

The calculation will also confirm the width of the perimeter zone.

Regardless of the type of membrane attachment, mechanical fasteners are always required at the roofs perimeter, angle changes and any details. This ensures that any tensions generated in the field membrane are not transferred to other areas.

In warm roofs, the insulation boards may also be mechanically attached. This should always be kept separate from the attachment of the waterproofing membrane.
Icopal recommends that Insulation boards should be secured at a rate of 11 fasteners per 2400 x 1200mm (3.8 fixings/m²)

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