IHBC Yearbook 2017

36 Y E A R B O O K 2 0 1 7 the case and other companion guides to the Building Regulations such as BS5250:2011 Code of Practice for Control of Condensation in Buildings are weak in their understanding of breathable structures and only deal adequately with modern buildings or with one aspect of moisture, like condensation. A more integrated approach to all moisture types which deals specifically with solid wall construction is necessary to reduce moisture risks. It should be noted that there are still many uncertainties about moisture risks in all buildings. At all times, therefore, a precautionary approach should be taken and as much information as possible should be gained in any project through good assessment, monitoring and feedback. CATEGORIES OF ELEVATED RISK To understand the risk of undertaking external wall insulation (EWI) on an older building it is important to understand where the risks lie and what can be done at the process and planning stage to minimise them. Research undertaken in this area by the BRE, STBA, SPAB and others demonstrates that there are key stages where risk is most elevated. These can be categorised as set out below. Surveys that do not consider these issues should be considered poor. Fabric What is the building made of? Can EWI be fixed to it (for example, some traditional building materials are very weak)? Location Where is the building? Does it get a lot of wind and rain? Is one side more exposed than the others? A building on a cliff in Wales is very different from one on a London street. The more exposed the building is, the more care should be taken over detailing – extended overhangs, wider gutters, proper splash protection and mastic-free seals around windows, for example. In exposed locations the exposure of walls to wind- driven rain should be assessed using BS 8104 – this is vital for determining material suitability. Other factors such as proximity to sources of deposition (such as industrial outlets, motorways and other sources of airborne pollution) should also be considered at an early stage because they will reduce the robustness and effectiveness of the insulation. Significance Are there planning constraints or heritage values ascribed to the building as a whole? Form Has the building got a complicated shape or details which make it difficult to be sure that there won’t be leakage or cold bridging? Does this form have heritage value? If it is complicated, it may be better not to insulate or to consider internal wall insulation. Condition Is the fabric wet internally? Is the building already suffering from damp? If so, has it been assessed correctly? Is it in such a condition that it should be insulated at all? Fixing insulation on damp or defective buildings EWI should not be fitted to wet or damp buildings, which need to dry out before being clad, or which need repair (for example, due to high ground levels, leaking roofs, ill-conceived damp-proof courses, and poorly designed and constructed replacement floors). The moisture may be driven into the building by wind or other natural occurrences. Ventilation Covering up ventilation by reducing infiltration rates and making the building less draughty is another common cause of risk. Understanding how the insulation will affect the ventilation of the inside is essential to ensure that it does not create unhealthy living conditions. If already installed, ventilation should always be checked for correct installation and operation at design capacity, and if not installed, assessed and installed where necessary. The main weakness in this area is not knowing how to assess that the building is in moisture balance and how much ventilation is adequate. Rain during application Insulation systems sometimes get wet during application or because of poor storage or delivery methods. This can lead to failure of the insulation and render systems from excessive moisture and freeze-thaw cycles. Insufficient caution A lack of understanding, skills, budget or time can lead to errors, short-cuts and poor quality work which can cause a variety of moisture risks. THE WHOLE-BUILDING APPROACH In short, the building should be considered as a single entity and a whole-building approach should be used. To fully consider the risk to the building and its inhabitants it is essential that work does not proceed unless it is based on complete and accurate information. The building should not be insulated until the following factors are known and understood: • how the building was constructed and with what materials • the moisture content of the structure and how the introduction of insulation will affect it • the consequences of isolating the external wall from solar gain and wind drying • the context location, exposure of the building and the climatic conditions that the structure will be exposed to over its life-span • the ventilation provision in the building, the occupants’ ability to operate it accordingly and the consequences of their failing to do so. If all of these factors are known and the materials and workmanship are of a very good standard, then the introduction of insulation to the external walls might be the right option. However, it is important to remember that nothing is maintenance- free and that failure to maintain a building will result in it failing. Colin King is director of the Building Research Establishment (BRE). Standard detail around a telephone junction box introducing a large cold bridge and the potential for moisture damage