Thermal retrofits of homes are central to the UK's fuel poverty and net zero carbon policies but there are concerns about poor quality installation and so new standards are to be introduced (PAS2035). We have explored retrofit installers' perceptions of the barriers to installing internal wall insulation (IWI) and of current regulations and standards for retrofits. We conducted four focus groups with retrofit installers. Thematic analysis identified three themes. (1) IWI is viewed as impractical in situations other than new builds, extensions and conversions as it is too time-consuming and expensive. (2) Installing IWI is perceived as an unskilled job with no need for training or referring to standards during installation. (3) Because standards lack credibility, installers can be sceptical of potential problems caused by on-site installation adaptations, for example thermal bridging. Our results show that retrofit standards have not improved retrofit quality. Awareness and credibility of standards is low, and new standards (PAS2035) will introduce additional costs which may reduce the pool of installers willing to engage in the retrofit market. Policies need to address installer training, professional identity and social practices, and reduce barriers to change in order to increase success.

房屋的热改造是英国燃料匮乏和净零碳政策的核心，但人们担心安装质量差，因此将引入新标准 (PAS2035)。我们探讨了改造安装者对安装内墙保温材料 (IWI) 的障碍以及改造的现行法规和标准的看法。我们与改造安装人员进行了四个焦点小组。专题分析确定了三个专题。(1) IWI 在新构建、扩展和转换以外的情况下被认为是不切实际的，因为它太耗时且成本高。(2) 安装 IWI 被认为是一项不熟练的工作，在安装过程中不需要培训或参考标准。(3) 因为标准缺乏可信度，安装人员可能对现场安装调整（例如热桥接）引起的潜在问题持怀疑态度。我们的结果表明改造标准并没有提高改造质量。标准的认知度和可信度较低，新标准 (PAS2035) 将引入额外成本，这可能会减少愿意参与改造市场的安装人员的数量。政策需要解决安装人员培训、专业身份和社会实践问题，并减少变革障碍以提高成功率。