Safintra explains the basics about getting roofing systems, incorporating insulation, to deliver what they should for owners, occupants and the environment.
Common ways of installing insulation as part of the roofing system are to either lay it on top of the ceiling or under the roof covering, over purlin. However, the use of thick and bulky insulation presents issues of stability for the roof sheeting, and if the insulation, whether bulk or rigid, is severely compressed, its performance is questionable.
If used under pierced fixed sheeting, the long fasteners are put under high stress and when installed under concealed fix sheeting, the concern is that thick blanket insulation will bulk up under the sheet and could force the sheet off the clip securing it.
In addition, for insulation to perform at its optimum level and achieve the R-value prescribed by SANS 10400 XA, a continuous layer must be installed with minimal compression or thermal bridging.
Various methods have been developed to address these challenges, such as using u-shaped stirrups or spacers, installing a row of timber purlins or packers which are fixed to the lower row of purlins over the insulation, using metal straps or secondary metal purlins. None of the above methods are successful in preventing that the performance of the insulation material is compromised by the method of installation.
A properly engineered roof spacer system such as Ashgrid® will, by creating a defined cavity or roof space, accommodate blanket insulation at its full depth. Such systems are pre-engineered for rapid and easy installation, and have varying leg heights for various depths of insulation. The resulting R-values of the insulating material may therefore be taken at full design value as stated by the manufacturer.
Testing the performance
Safintra South Africa initiated tests to determine the performance of an insulation blanket installed with its concealed-fix system, Saflok®.
A 135mm fibreglass blanket with a density of 12kg/m³ was installed under the sheet and over purlin. Straining wires were installed with sufficient slack to allow the insulation to maintain as much loft as possible between purlins, within practical considerations. Saflok 700 was installed as the roof covering.
The first test was conducted without a roof spacer system and the second using the Ashgrid® roof spacer system.
The tests clearly showed that:
1. The integrity of the Saflok system was unimpaired, with the clips securely locking the sheeting over the blanket, which had compressed to 15mm.
2. That compression of the insulation blanket at the purlin compromised the thermal performance of the insulation by almost 40%, whereas the roof spacer system allowed the insulation to perform to its full design value.
Safintra further highlights that the cost of a roof spacer system with properly performing insulation is in most instances lower than the cost of additional layers of insulation to achieve the required R-value in the roof space.
135mm insulation without Ashgrid spacer system 135mm insulation with Ashgrid spacer system
Design thickness 135mm 135mm
Design R-value m².K/W 3,375 3,375
Design thermal conductivity W/(m.k) 0,04 0,04
Maximum depth achieved (mm) 85m 125mm
Minimum depth achieved (mm) 15mm 110mm
Average depth achieved (mm) 65mm 120mm
Actual R-value m².K/W 1,772 3,0
A comparison of 135mm insulation installed with and without the Ashgrid spacer system.
Caption: Without a roof spacer system, the 135mm thick insulation is compressed to 15mm at the purlin, reducing the thermal performance by almost 40%.