ETAG 031 is part of a family of European Technical Approval Guidelines (ETAGs). It was prepared in 2010 under the Construction Products Directive (CPD) – now the Construction Products Regulations (CPR) – to provide a basis for the consistent assessment of inverted roof systems throughout Europe.

Its guidance covers a thermal insulation material, used in conjunction with either a filter layer, a separation layer or water control layer (“water flow-reducing layer”). Together these two components are known as the ‘kit’, for use on a flat roof – which ETAG 031 defines as any roof with a pitch less than 8.5 degrees. (The typical definition of a flat roof is a roof with a pitch less than 10 degrees.)

Are inverted roof solutions “ETAG 031 approved”?

An ETAG can be used by a formally recognised assessment body to issue European Technical Assessments (ETAs). An ETA is typically obtained for products where no harmonised European standard exists, which can then be CE marked.

Thermal insulation materials used in inverted roof kits are the subject of their own harmonised European standards (such as EN 13164 for XPS), so obtaining an ETA is unnecessary. ETAG 031 references these harmonised standards when specifying how insulation performance should be tested and declared.

Kits are assessed for a conventional Agrément certificate (such as a BBA certificate) as normal. The product is not necessarily assessed directly against ETAG 031 (the BBA certificate for Polyfoam’s inverted roof system makes no mention of the document), and so is not “ETAG 031 approved”.

However, the insulation is essentially manufactured to conform to the technical standards in ETAG 031. By extension, that makes assessment and Agrément certification a lot more straightforward. ETAG 031 remains widely referenced in the inverted roofing sector, as it includes guidance on how to assess the performance of inverted roofs as a whole.

What components of an inverted warm roof are part of ETAG 031?

The inverted roof ‘kit’ comprises the thermal insulation layer and the water control layer.

Above the kit, components – such as gravel ballast, paving, drainage layers, bedding layer material and growing medium – are considered in a “set generic specification” in terms of how they affect, or may be affected by, the performance of the kit. Any of these components, in combination with the kit, make up the inverted roof ‘system’.

Waterproofing is installed below the system on the structural deck. It does not depend on the inverted roof system for its own performance, and nor does it contribute to how the system functions. Waterproofing is therefore not a consideration in ETAG 031.

What thermal insulation is appropriate for an inverted roof system?

ETAG 031 says the thermal insulation layer should be extruded polystyrene (XPS) manufactured to EN 13164, or expanded polystyrene (EPS) manufactured to EN 13163. It should feature either a butt joint, rebate joint or tongue and groove joint.

Insulation should be loose laid and not subjected to direct trafficking. Where the finished roof will be trafficked, the protective overlay should be appropriate to the intended use.

XPS insulation is classified as suitable for untrafficked, pedestrian and parking deck roofs, as well as green roofs and roof gardens. ETAG 031 can only be used to assess EPS for untrafficked and pedestrian roofs, as that type of insulation has a “limited history of use in green roofs and roof gardens”.

The fire performance of inverted roof systems is covered in this blog post.

About Polyfoam Roofboard solutions

Polyfoam Roofboard Extra, manufactured by Polyfoam XPS, is manufactured to EN 13164. Combined with Polyfoam Slimline Zero membrane acting as a water control layer, it is certified by the BBA as an inverted roof solution.

It has a declared thermal conductivity of 0.033 W/mK, and a design thermal conductivity of 0.034 or 0.035 W/mK depending on thickness. To find out more about design thermal conductivity and how it is calculated in accordance with ETAG 031, read our follow-up blog post (coming soon). The post also describes how a rainwater cooling effect for inverted warm roofs is calculated in accordance with ETAG 031.

Polyfoam XPS also manufactures Roofboard Super, an inverted roof insulation designed for car parking decks or roofs expected to receive significant levels of foot traffic.

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