Thermal Insulation: Avoiding Risks

Research has shown that technical issues that were not important for uninsulated constructions may become more significant when they are better insulated. For example, certain parts of the construction remain colder and create a greater risk of interstitial condensation, and changes to traditional forms of construction to improve the insulation could lead to damp penetration. It is important to anticipate these effects and, by a better understanding of the physical principles involved, avoid the risk of building defects occurring. With traditional building, there was often a considerable safety margin inherent in the construction. With increased levels of insulation, this may be less so, and correct design and specification, as well as careful attention to good workmanship and supervision, may be necessary to ensure trouble free building. Also, in some situations, builders may prefer to select more robust forms of construction. This guide explains the technical risks which may be associated with meeting the building regulation requirements for thermal insulation (conservation of fuel and power) for the major elements of the building: roofs, walls; windows; and floors. For roofs and floors, there are further subdivisions within each element, often related to the insulation system or its position within the construction. The report concentrates on load bearing masonry, timber frame construction and, in some respects, profiled sheet cladding. Within each subject area, explanations of the more important technical issues are highlighted and are followed by actions that could be taken to avoid the risk of failure. Illustrations show construction principles and selected examples of good practice detailing. These examples are not exhaustive and designers and builders may have well established details using other materials that are equally suitable. Throughout the guide, illustrations are numbered 1 to 94 and recommended actions, 101 to 483. The information in the guide represents the recommendations of BRE on good construction practice associated with meeting the required thermal standards. It does not give guidance on which constructions meet particular U values. The guide has been prepared with specific reference to Part L of the Building Regulations for England and Wales, but the potential technical risks and recommendations for avoiding action apply in principle throughout the United Kingdom. This document is not an Approved Document under the Building Act 1984.

Table of Contents:
Introduction; potential risks. Part 1 Roofs: pitched roofs - tile or slate; flat roofs - cold deck, warm deck (sandwich), warm deck (inverted); pitched roofs - profiled sheet. Part 2: walls. Part 3: windows. Part 4 Floors: concrete ground floors - insulation below a screed, insulation below a board, insulation below a slab; timber suspended floors - insulation between joists; upper floors - intermediate floors, exposed soffit floors.