Jablite is the UK's largest producer of EPS products for insulation and civil engineering applications

Why Over-Specify Inverted Roof Insulation?

The current habit of routinely specifying 300 grade XPS or EPS insulation for inverted roofs makes no sense, says Richard Lee, Managing Director of Jablite Insulation

October 2013: Richard explains: “We believe that 300 grade inverted roof insulation is specified when, in the majority of cases, it is unnecessary.

“We conducted a rigorous performance analysis of Jablite 200 and 300 inverted roof insulation grades and confirmed they provide an identical thermal performance and both are BBA certified and ETAG 031 approved.

“The difference in compressive strength is 90KN/m² for Jablite 200 and 120KN/m² for Jablite 300.

“For the majority of pedestrian traffic roofs the design load performance of Jablite 200 is more than sufficient.

“XPS insulation boards are only available in 300 grade and some 300 grade XPS boards have a lower design load capability than Jablite 200!

“Naturally, we began to wonder if habit has led to an unquestioning over-specification of insulation for inverted flat roofs.”

Jablite insulation for inverted roofs is BBA certified for use on zero fall flat roofs, balconies, terraces, green roofs and all slopes between 1:80 and 1:6.

Jablite consulted structural engineers, contractors and membrane suppliers. “The advice we have received is that the difference in compressive strength – in the majority of cases – has absolutely no impact,” says Richard.

Loads imposed by roof-top plant vary from project to project and largely depend on the self weight of the units and the type of bearing design specified.

A simple calculation determines the design load requirements of the insulation and in most instances 200 grade Jablite FRI fits the bill. In fact, specifying 200 grade material reduces the total insulation weight and therefore the load on the roof deck.

And, as Steve Broadhurst, Technical Services Manager, comments: “For those situations where heavier-than-usual load bearing is required you still have the option to specify the 300 grade material. Either way Jablite FRI provides the solution.”

In addition, all Jablite insulation for inverted roofs is available in 1mm increments and can be ordered to exactly meet the specified U-value requirements of the project – making Jablite insulation by far the most cost-effective option.

Jablite’s technical experts will provide detailed performance analysis, including load bearing and U-value calculations to help you specify or select the most appropriate inverted roof insulation for any project.

So why would anyone routinely over-specify 300 grade insulation, when you can make an informed choice and cut down the overuse of material and reduce unneeded material thickness?

“We think specifying 300 grade insulation for inverted roofs has become a habit, it is time to challenge that and to offer an alternative, more precise specification option,” says Richard.

“It makes economic and sustainable sense to specify what is needed – for nearly all inverted roofs with pedestrian traffic; Jablite 200 performs well within the design load parameters.”


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