With a skillion roof the traditional air space between ceiling and underside of roof is insulated. Skillion roofs may be finished in different materials, but the most common in New Zealand is still profiled metal roofing. (See Industry Solution 11C) Skillion roofĪ skillion roof is where the ceiling line is parallel to the roof line, with only roof structure between. With the new H1 requirements calling for a much higher level of insulation (R6.6) in residential and small buildings, the system will prove attractive to architects but will require a very different way of detailing roofing junctions, particularly if skillion roofs are used. The use of insulation above the structure, beneath the roof membrane, means interior components are kept warmer which reduces the risk of condensation within the build-up, resulting in a drier home for all. Manufacturers and suppliers of roofing systems have developed specific products and details to comply with the design conditions of warm roof construction. Therefore there is often no insulation layer required at ceiling level. Here the insulation is applied continuously above the structure so that everything within the building envelope is kept insulated, including the structural parts of the roof. The warm roof solution is more common overseas but will become more usual in New Zealand over time, due to MDH. Some methods of heating and cooling using the roof void may need to be modified (refer to Chapter 12 on Services). Ensure that the thermal barrier is continuous from roof to wall, avoiding these thermal bridges. It is possible that we will need to develop new details at this junction, or possibly new insulation materials to create adequate R6.6 insulation rating at this area and to avoid thermal bridges. It will be extremely difficult to install and maintain at the junction between the wall, ceiling, and roof plane. Thermal batts will sit very high above ceiling level, and potentially be subject to crushing from anyone moving around in the attic space. The new H1 requirements for much higher levels of roof insulation ( R-value 6.6 for residential in all 6 climate zones and up to 7.0 for large buildings over 300m ²) will mean an extensive build-up of insulation at ceiling level. For excellent detailed information refer to the Metal Roofing Design Guide (NZMRM, online) and SMACNA and NRCA documentation. This is a major step forward to speed up and simplify traditional roof-building. Recent advances in metal roofing mean that fleecy-lined roofing can be installed quicker and easier, reducing the chance for moisture to drop from the underside of the metal roof and removing the need for the layers of chicken mesh and tar paper (see COLORSTEEL Dridex® later in this chapter), although a dedicated water-resistive barrier is still required. Although this is crude and more sophisticated building wraps can now be used, this is still the way the majority of roofs in Aotearoa are currently built. Condensation forming on the underside of the metal roof drops onto the building paper and runs down to the outside gutter. Heavy strength building paper is installed, traditionally supported on chicken wire mesh to stop it sagging between purlins and rafters. The dew point of condensation is therefore inside the thermal envelope, so traditionally-designed profiled metal cold roofs require condensation to be caught or the moisture ventilated so it does not infiltrate the insulation and the house below. The term cold roof means that the insulation is set below the actual water resisting layer, often at ceiling level. There are two primary roof systems, a cold roof (our traditional solution) and a warm roof. Clearly, items such as watertightness, safety, maintenance, sight lines and height limitations are important factors when dealing with roof design – but let’s start with the basics. After the Sk圜ity convention centre fire it is likely there may be new regulations around fire for roofs. Roofs are obviously a vital part of waterproofing MDH, and correct design and installation is important given the height above ground.
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