Solid Wall Terrace Retrofit Research Project.

Pre-1919 solid walled housing is commonly referred to by the acronym HTT (Hard to Treat) owing to the difficulty in bringing its fabric up to the thermal standards required to meet our 80% carbon reduction targets by 2050.

This study used IES dynamic thermal simulation to examine the particularities of the heating season performance of the solid walled brick terrace: arguing that the terrace's reduced external surface area puts it in an advantageous position to be a thermally efficient form of housing, once the deficient aspects of the surface to air fabric are modernized. It sought to determine whether the inherent thermal mass of the existing structures is an important resource to be harnessed with the application of External Wall Insulation (EWI).

The simulation is based on (and it's performance compared to) a typical mid-sized brick terraced house in Sheffield to gain assurance that it is reflecting real-world conditions. This revealed subtleties to the party wall heat transfer between neighbouring houses, and lead to a novel means of simulating their performance while admitting the influence of their thermal mass - which is found to be an important factor.

The design solutions used for the simulated improved building are predicated on the philosophy of natural fibre hygroscopic materials, which are more likely to work in composite with the existing vapour permeable building fabric - so the resultant elemental u-values are inferior to those which would be achieved with high performance synthetic insulants. The study however sought to determine whether what my be deemed "super insulation" is actually required, given the diminishing scale of improvement found to be achieved with exponentially thicker layers - it is a notional rule of thumb that the first 75mm of insulation will save over 80% of the energy (over an uninsulated wall), the next 75mm a further 7%, the next 75mm a further 2%. The effect of three different levels of insulation is therefore analysed against resultant energy savings, physical building conditions, and thermal comfort, to gain insight into what might form optimised design solutions for the retrofit of the solid brick terrace for desired internal conditions. The study also questioned contemporary notions of domestic thermal comfort, arguing that an adaptive principle is, in tandem with building improvement, an essential part of the solution.

The graphs shown below demonstrate that it is indeed the case that there is a law of diminishing returns when it comes to increasing the thickness of insulation, they also demonstrate that introducing a basic amount of insulation significantly improves the mean radiant temperature at a given air temperature and therefore the perceptible thermal comfort of a space.