Traditional Whole House Retrofit at Ton Pentre: monitoring results

STBA Responsible Retrofit Series: Whole House Retrofit Ton Pentre
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The case study report on a multi-year project to deliver and assess a whole house retrofit of a small solid wall mid-terrace home in the South Wales Valleys has just been published.

The Sustainable Traditional Buildings Alliance (STBA), which is managed by the SDF, worked in partnership with RHA (formerly known as Rhondda Housing Association) to carry out the retrofit at a void 2-bed mid terrace pre-1919 dwelling in Ton Pentre. The project was co-funded by the Housing Association and the BEIS Thermal Efficiency Innovation Fund (TEIF) – see here for the full report.

The project began in 2021 with an initial survey, which made use of the STBA Survey Tool. This tool has been designed with PAS2035 in mind, and collects sufficient data in detail to enable design decisions to be made with minimal risk.

The retrofit took an innovative approach to insulating the solid rough stone rear wall. Made of random local sandstone bedded in lime mortar (with a high proportion of coal dust waste used as an aggregate), it was insulated internally using 40 mm of lime plaster enhanced with an aerogel filler, and rendered externally using air lime and limewash. The system was designed to achieve good thermal performance with a low moisture risk.

The retrofit was completed in 2022, and the case study report comes out now with the first year of post-occupancy monitoring already completed. Results show that an excellent internal air quality and indoor comfort have been achieved, and the measured U-value on the rear wall – 0.53 W/m².K – is even better than predicted. The first monitoring report is available on the SDF website, and monitoring will continue for a further two years.