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Insulate Magazine Issue 11 - October 2017

When is an Insulation Manufacturer not and Insulation Manufacturer headlines the October issue of Insulate Magazine. Possibly the best front cover for an Insulation publication EVER.

The only independent

The only independent insulation industry trade magazine Insulate Debate Warm Flat Roofs are Simply the Solution when it Comes to Quality and Performance warm flat roof, correctly designed, specified and built, is one of the simplest construction A elements of the building envelope, writes Paul Forrester, Technical Services Manager at PIR insulation manufacturer, Recticel. However, its performance remains reliant upon a basic, but essential value: high-quality workmanship. Structural deck, vapour control layer, insulation and waterproofing combine to create a warm flat roof; the perfect example of a fabric-first approach in action. It’s a tried-and-tested solution, not least because it keeps the roof structure at or around the same temperature as the building interior. This eliminates the possibility of condensation occurring - which could otherwise cause deterioration of the structure - and ensures the roof performs for the building’s intended lifespan. And yet questions such as, “Does a roof need a vapour barrier?” continue to be asked, highlighting that misapprehensions remain about the ramifications of flat roof design. Too often, poor roofing performance results from a lack of awareness good-practice principles. A warm flat roof, correctly designed, specified and built, is one of the simplest construction elements of the building envelope. However, its performance remains reliant upon a basic, but essential value: high-quality workmanship. 26 insulatenetwork

www.insulatenetwork.com Space Consideration Compromises can also be caused by on-site constraints, a good example being that of hybrid roofs. Imagine a flat roof constructed on timber deck and joists: it’s not surprising that people sometimes look at the space between joists and wonder if it can be filled with additional insulation. If there is a restriction on the thickness of insulation that can be accommodated above the structure, then the temptation to utilise the extra space is even greater. However, problems can occur if a standard warm roof is designed and constructed, but with additional insulation incorporated below the deck. Not only is a vapour barrier or vapour control layer (VCL), a vital component of the roof, it must be correctly positioned - on the warm (internal) side of all the insulation. There are numerous reasons why incorrect placement of insulation relative to the VCL should be avoided, perhaps best summarised in the foreword of BS 5250:2011 + A1:2016 Code of practice for the control of condensation in buildings, which states: ‘Bearing in mind that occupants often fail to use buildings There are numerous reasons why incorrect placement of insulation relative to the Vapour Control Layer (VCL) should be avoided in the manner intended, be it by choice, lack of understanding or force of circumstance, designers are advised to err on the side of caution and adopt robust, fail-safe solutions.’ Label with care To that end, section H.2 of the standard lists three acceptable scenarios for the placement of insulation in a flat roof: cold roof, warm roof and inverted roof. Nowhere does it support the design and construction of hybrid flat roofs. Some insulation manufacturers, however, are happy to advocate hybrid constructions, usually when the balance of the two insulation thicknesses is considered to be “correct”, i.e. the layer of insulation between the joists does not have higher thermal resistance than the layer of insulation installed over the deck. A condensation risk carried out in accordance with the method detailed in BS EN ISO 13788 insulatenetwork 27