Insulated roofs spacer systems are best installation practise

This article is part 3 of a series on sustain-ability in the built environment, aimed at professionals, specifiers and owners looking to green building best practise. They focus specifically on the role played by metal roofing and cladding systems in creating better buildings.

Detailed installation methodologies for insulated roof spaces are often over-looked at design stage. As a result the insulation performance may be negatively affected during the on-site installation process, and not achieve prescribed R-Value’s stipulated in the SANS 10400XA standards.

Of key importance, it is imperative that insulation maintains its full design depth throughout the roof assembly in order for it to achieve its R-value. Compression of insulation compromises the R-value & thermal performance of the material.  It also increases thermal bridging along purlin lines.
Factors such as cost, aesthetics, thermal performance & combustibility all play a major role in the selection of an appropriate insulation material for a project.  

Rigid insulation boards & flexible insulation blankets are the two most popular types of insulation used in commercial roof assemblies in South Africa.

  • Rigid insulation boards generally cope better under compression but as their specified depths increase so do the associated costs, and increased risks with long fasteners and system instability.
  • Flexible blanket insulation installed over purlin will be subjected to considerable compression along the purlin lines if the outer weather sheet is not elevated. Suitable spacer systems should be employed in these instances to prevent or reduce compression.



There are various forms of spacer systems available in South Africa.

Continuous spacers or ‘packers’ are available in a number of forms such as Timber, XPS or Steel. They are secured directly to the purlins in continuous lengths on top of the insulation blanket which is draped over purlin.

  • Packers will cause compression at the purlin but allows the blanket to regain some loft between purlins by elevating the weather sheet.
  • It is necessary to compensate for this loss in overall R-value by increasing the depth of the specified insulation blanket and packer accordingly.  (See table)

Mechanical spacer systems form the backbone of site assembled roofing systems where warranted   thermal performance is required. They eliminate compression of the insulation blanket and take the guesswork out roof assembly performance.

  • Lightweight structural steel bars (acting as purlins) are mechanically locked into each other to create the lengths required.
  • The bars are supported by brackets, which are available in a variety of heights to accommodate varying blanket thicknesses. The support brackets create a defined cavity for the insulation material and keep fasteners within safe working lengths. Specific loading requirements are achieved by varying the support bracket centres.

TABLE:  R-Value’s achieved by 135mm Glass Fibre Insulation Blanket using various Spacer & Packer options:

Table R Values

For further information contact Safintra: /
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Branches in SA : Johannesburg, Durban, Cape Town, Nelspruit, Polokwane, Port Elizabeth, Bloemfontein
Further operations in:  Namibia, Zambia, Mozambique, Malawi, Tanzania, and East Africa.