The focus of the 2013-2014 Springboard-funded Postgraduate Certificate in Digital Analysis & Energy Retrofit programme was a study of a Scottish multi-unit residential social housing building typology which the UK Building Research Establishment had constructed on their Ravenscraig research park near Glasgow. Their study building was called ‘4-in-a-Block’.
Each student was required to develop a deep energy retrofit design proposal for this ubiquitous Scottish inter-war housing typology which is also the subject of British Research Establishment (BRE) Scotland research and monitoring. The project performance requirement was the now well established (in DIT) Nearly Zero Energy Building (NZEB) rating of 45kWh/m2a.
The project also provided the means to compare the Irish Dwelling Energy Assessment Procedure (DEAP) with the UK Standard Assessment Procedure (SAP). The typology was chosen because of its similarities to the form of the reference dwelling in DEAP which should have resulted in very predictable energy balance calculations.
The differences between SAP and DEAP were startling with one of the near Passive House standard Scottish retrofitted apartments rating best in SAP (86) and worst in DEAP (D1). The primary energy factor of mains electricity seemed to account for most of the discrepancies, underlying how central this factor is when DEAP is used to inform design choices. With its primary focus on carbon emissions, SAP seemed more accepting of electrically-based heating solutions.
An analysis of the lifecycle cost of various retrofit measures, using the Energy Performance of Buildings Directive methodology was incorporated into the study. This tended to penalise the use of mechanical systems with ongoing annual maintenance costs and short life spans like gas boilers or solar thermal hot water systems. The fact that these were highly regarded in both SAP and DEAP suggested that recalibration of both national methodologies was required to align with the EPBD principle of cost optimality. Recalibration of the primary energy factors is under active consideration in both methodologies in 2018.
A review of the standard of airtightness delivered by the BRE contractors revealed an average q50 of 6.7 m3/m2h, approximately ten times the minimum air leakage rate allowed for the certification of a Passive House. Even NZEB retrofit typically demands q50 pressurisation test results in the 1-2m3/m2h range to ensure economical sizing of ventilation and heating systems. (To put this in context the record in 2018 is 0.07 m3/m2h - almost 100 times more airtight that the BRE apartments).
Good levels of airtightness are also required to avoid the damaging effects of “interstitial condensation”, which must be assessed and controlled under Irish building regulations. Such poor standards of construction were not expected in the BRE test block and turned out to have been largely a result of the relatively open method of procurement used by BRE which was reliant on volume UK house builders to provide non-volume retrofit services on a semi-voluntary basis. The leakiness of the construction was (correctly) heavily penalised in DEAP, especially when MVHR systems were included.
Over fifteen project designs were produced by a class of architects and architectural technologists using a variety of digital modelling and environmental design software applications. One of the more successful student projects employed an external airtightness layer, a technology that has since become relatively commonplace in problem NZEB retrofit projects, but only when condensation risk is well analysed and controlled for.
These are selected posters of the ‘4-in-a-Block’ project: