D & D Roof Insulation uses the ASHRAE zone method to compare the thermal resistance performance of faced fibre roof insulation installed with and without Insultrak.


In order to compare the thermal resistance performance of faced fibre roof insulation installed with and without Insultrak™, the manufacturers of the system (D & D Roof Insulations) recently applied the ASHRAE method so that they could determine whether roof insulation spacers in over-purlin, fibre-glass roof installations offered any advantages.

What is the ASHRAE zone method?

The ASHRAE zone method is a series/parallel calculation of heat flows and incorporates an edge effect zone that approximates the tendency for heat to enter and leave highly conductive elements, which might intrude through a system (ASHRAE Fundamentals Handbook 2009, Vol. 27.5). The calculation of width of edge effect is in accordance with guidance given in ISO6946.

Results of the exercise
The results may be summarised in absolute terms or as a percentage reduction relative to an installed thickness of fibre insulation:

Thermal resistance (R-values in m2K/W):
•    100mm fibre insulation installed over-purlin under roof sheet without Insultrak™ – 1,49.
•    100mm fibre insulation installed over-purlin under roof sheet with Insultrak™ – 2,16.
•    Percentage increase in thermal resistance (R-value) with Insultrak™ – 45%.

The absolute value obtained correlates extremely well with the results of hot-box testing of installed 101,6mm (4 inches) fibre published. Graph caption: ASHRAE Fundamentals handbook 1985, table 5c.
ILZE to redraw

The calculated result is obtained by assuming a net average 60mm of effective thickness of fibre as a result of the caternary effect and the compression of the fibre by the purlins and supporting wires.
The average effective thickness of fibre with the Insultrak is similarly very conservatively estimated at 80mm. In practice, the fibreglass insulation achieves its full thickness of 100mm nearly across the full span of an 1 800mm purlin centre. The results of this study show that there are thermal advantages of roof insulation spacers in an over-purlin fibre-glass roof installation.

About D & D Roof Insulation

D & D Roof Insulation is one of the leading innovators and suppliers of most commercially available roof insulation products in South Africa for the past 15 years. Following previous product successes such as the development of Starlite®, which was the first faced fibre roof insulation material in South Africa to achieve an A1 fire rating, the development of a solution such as Insultrak was therefore a natural progression.

D & D Roof Insulation
Tel: 012 800 3606
Fax: 012 800 3835
Email: info@roofinsulation.co.za
Website: www.roofinsulation.co.za