Vocabulary
Terms and definitions on affordable and sustainable housing *
Thermal Insulation and Airtightness
Area: Design, planning and building
Increasing the thermal properties of the building envelope is a passive strategy to reduce energy loss and ensure significant reductions in energy demand (Grecchi, 2022). Van den Brom et al (2019) define thermal renovation as “renovation measures that are taken to reduce energy consumption used for thermal comfort”, and combines thermal insulation, airtightness and efficient electrical system into a single category. Accordingly, deep ‘thermal’ renovation occurs when significant improvement in at least three building components bring thermal performance to a level equal to or higher than the current building regulation standards (van den Brom et al., 2019). These building components include roof insulation, floor insulation, façade insulation, window improvements, heating system, domestic hot water system, and ventilation system (van den Brom et al., 2019). Other authors (Institute for Sustainability & UCL Energy Institute, 2012; Sojkova et al., 2019; Traynor, 2019) divide electrical systems into a further category for clearer practical application.
The concept of airtightness is revered for saving energy, avoiding structural damage, contributing to thermal comfort (Bastian et al., 2022), and is key to reducing heat loss through ventilation (Roberts, 2008). Draught proofing involves draught-stripping, replacing leaky windows and closing off unused chimneys (Roberts, 2008). The location of an airtight layer should be identified, and all penetrations through it minimised, sealed, and recorded (Traynor, 2019). This airtight layer can be airtight board, a plastered wall, or a membrane with appropriate tape at all junctions such as window openings (Traynor, 2019). Triple-glazed windows in combination with any frame material are the most efficient glazing system at reducing primary energy cost and CO₂ emissions (Sojkova et al., 2019). All air pockets should be sealed to prevent draughts and thermal bridging. Thermal bridging should be eliminated wherever possible but can also be reduced to the extent that no physical problems such as moisture and mould occurs, with low internal surface temperatures (Bastian et al., 2022).
There are many forms of insulation to consider during DER that considerably contribute to a reduction in heat loss. Filling external cavity walls with insulation can reduce heat loss through walls by up to 40% (Roberts, 2008). Ground floor insulation and roof insulation are also necessary steps in DER (Grecchi, 2022; Roberts, 2008; Traynor, 2019). Ground floor insulation can occur in suspended timber floors between joists or above solid concrete floors (Traynor, 2019). Roof insulation can be added between structural elements, or using a ‘cold’ roof solution, with insulation laid or sprayed over the existing ceiling (Traynor, 2019). Alternatively, green roofs can reduce the amount of heat penetration through roofs, playing a similar role to roof insulation. This is done by absorbing heat into their thermal mass alongside the evaporation of moisture but will require structural upgrades to manage the new load (Roberts, 2008).
External wall insulation (EWI) protects the building fabric, improves airtightness and is relatively quick and easy to install (Roberts, 2008). EWI can also help mitigate overheating by absorbing less heat than the original material, while allowing existing thermal mass from solid masonry walls and concrete to be retained within the insulated envelope (Bastian et al., 2022). The two main external insulation systems are ventilated rainscreen systems and rendered insulation systems (Roberts, 2008). EWI is inappropriate for historical building use because it will cover the historical architectural character. Gupta & Gregg’s (2015) preserved the original exterior façade by using internal wall insulation inside the front façade and EWI on all other façades. However, drawbacks to this solution can include loss of internal floor area, and reduced energy efficiency as notable heat loss can occur where the internal insulated wall meets the external insulated wall (Gupta & Gregg, 2015).
Created on 26-06-2024
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* This vocabulary consists of definitions of key terms related to the combined research conducted by the 15 early-stage researchers. Each term has multiple definitions, each connected to one of the three main research areas: Design, Construction and Planning; Community Involvement; and Policy and Funding.
The joint construction of this vocabulary allows the researchers' projects to be interwoven. As such, the vocabulary is a tool for conducting transdisciplinary research on affordable and sustainable housing.
Entries are reviewed by RE-DWELL researchers and supervisors. The vocabulary is updated regularly.