Heritage Retrofit

30 BCD SPECIAL REPORT ON HERITAGE RETROFIT FIRST ANNUAL EDITION UNHEATED AREAS It is important that ventilation requirements are also assessed and addressed for unheated areas of a building such as roof and sub-floor spaces. Where insulation or airtightness are improved in a home, this can make unheated areas colder and less well ventilated, particularly if measures are applied incorrectly (sub-floor vents being blocked by insulation, for example, or loft hatches being left uninsulated). For unused roof spaces, adding significant levels of ceiling-level insulation will make the roof space colder, increasing the likelihood of condensation and associated problems, and increasing the risk of water tanks and pipework freezing unless these are also adequately insulated. Moisture-related problems are exacerbated where gaps in the insulation and airtightness layer (such as loft hatches or spotlight openings) allow warm, moisture-laden air to enter the roof space, and where insulation blocks existing vents. While such problems may be minimised by good practice and attention to detail, additional ventilation may be needed in any case, typically in the form of eaves, ridge or slate vents, for example. It should also be borne in mind that in the UK’s temperate climate, external ventilation often admits warm moisture- laden air. As warm air can carry more moisture than cool air, condensation may occur in a void cooled by high levels of insulation. So, increasing ventilation levels can bring its own issues, and uncontrolled ventilation may simply add to the problem. Ventilation paths must be carefully thought through to ensure that the overall strategy is effective and appropriate, and avoids stagnant pockets of air. Ventilation in sub-floor spaces can already be compromised by the build-up of debris in the floor void and/or in and around vents, which again presents risks of condensation and associated issues. Any such blockages should be removed as part of a retrofit project, and care must be taken to avoid blocking up ventilation routes with insulation, and to increase ventilation provision if necessary. Where the building is in an area with high levels of radon, strategies for ventilation (both sub-floor and for the main building), airtightness and insulation will require particular consideration. SAFEGUARDING PERFORMANCE ‘Despite all efforts made in its provision, ventilation is still one of the most difficult aspects to safeguard in use.’ ( Designing Out Unintended Consequences , see Further Information) Once a ventilation system has been chosen, the key question is: how can its operation and performance be maintained in the long term? Or, more simply, how much risk can be designed out? This is a vital question, and covers the following considerations: • Design – is the designer experienced in traditional building retrofit and do they understand the systems under consideration? • Installation and commissioning (particularly for higher-end ventilation systems) – is a specialist installer being used, or at the very least is the installer familiar with the selected system? Leading on from this, will the system be commissioned by an expert? • Control and use – are the end- users engaged? How simple can the system and its controls be made? How foolproof is the system? How will users know if it fails? Are the maintenance needs clear? What are the consequences of failure? • Supplementing ventilation provision (leading on from the previous question) – is supplementary ventilation available (use of windows, for example) in case of system failure? To maximise chances of success, insulation must be considered alongside airtightness and ventilation, following a whole-building approach to retrofit. Worst-case scenarios must be anticipated and risk designed out accordingly – this will often lead to simpler, more foolproof solutions rather than overly-complicated designs. The building must be considered in the context of its users and their behaviours. Experienced designers, installers and commissioners must be used, and occupants must be involved from the outset and be made fully aware of any behavioural impacts and maintenance needs in the future. At the heart of all this lies understanding: ‘Regardless of your reasons for retrofitting, the key to success is understanding. Understand your home, your lifestyle, your environment, your priorities, the upgrade measures available, the importance of careful planning and detailing, and the whole-house approach and joined-up process’. ( A Bristolian’s Guide to Solid Wall Insulation ) Further Information Bristol City Council/STBA, A Bristolian’s Guide to Solid Wall Insulation , BCC, 2015 (http://bc-url.com/bristol ) C King and C Weeks, Designing Out Unintended Consequences When Applying Solid Wall Insulation , BRE, 2016 (http://bc-url.com/insulation ) N May and N Griffiths, Planning Responsible Retrofit of Traditional Buildings , STBA, 2015 (http://bc-url.com/retrofit ) Royal College of Physicians, Every Breath We Take: The lifelong impact of air pollution , 2016 (http://bc-url.com/air) T Sharpe et al, Characteristics and Performance of MVHR Systems , Innovate UK, 2016 (http://bc-url.com/mvhr) R Sharpe et al, ‘Higher Energy Efficiency Homes are Associated with Increased Risk of Doctor-diagnosed Asthma in a UK Sub-population’, Environment International , Vol 75, 2015 (http://bc-url.com/asthma) Zero Carbon Hub, Ventilation in New Homes , 2016 (http://bc-url.com/vent) NICHOLAS HEATH is an independent sustainable energy consultant specialising in traditional and historic building retrofit. He is director of NDM Heath Ltd, associate technical director of the Sustainable Traditional Buildings Alliance, a qualified SAP and BREEAM energy assessor and the author of numerous research publications and technical guides. Condensation on a window pane is often a good indicator of inadequate ventilation. A 1930s copper cupola providing passive stack ventilation on a former school building in Bath