The Northern Ireland Housing Executive has published an account of a retrofit pilot project to improve five houses to different energy efficiency standards. The scheme was completed in 2018, followed by two years of post-occupancy evaluation. The purpose of the pilot was to understand the benefits and challenges of implementing various retrofit measures, which would then inform the strategy for future retrofit schemes on a much larger scale. The aim of this report is to disseminate the lessons learned to stakeholders who may be considering, or are currently undertaking similar retrofit work, perhaps for the first time. This may include but is not limited to Housing Associations, homeowners, designers, students, policymakers and government bodies. The report describes the process from its very early, ambitious beginnings, to the detailed and target-driven approach finally delivered.
In summary, the five houses were chosen for their similarities in terms of location, orientation, size and layout, making them suitable for comparative purposes to demonstrate the impact of applying different packages of measures. The Standard Assessment Procedure (SAP) was the method of calculation to determine the pre and post-retrofit energy efficiency rating, with one house required to meet a high SAP B, one low SAP B, one high SAP C, one low SAP C and finally a privately owned property that was to meet a SAP C of any level.
The design was developed through collaboration with industry leaders, BRE and MosArt and aimed to improve energy efficiency primarily through fabric-first measures, with limited renewable energy solutions.
We were grateful to have Bryson Energy help fund the works to the privately-owned house, which allowed us to complete the aesthetics and thermal continuity of the terraced row.
We were also resolute in our desire to appoint a main contractor with relevant experience in many of the measures we implemented. This worked well as BlueBuild Developments were able to bring their expertise in EWI and renewable energy installations and were extremely forthcoming in helping us to achieve our energy targets.
The measures implemented included external wall insulation, loft insulation, gas boilers, heating controls, new windows and doors, improved construction detailing to reduce thermal bridges at critical locations, an airtightness strategy, and innovative ventilation systems.
The following is an overview of the outcomes of the scheme, of which more detail can be found in the report ‘Journey to Retrofit’.
There are many examples of published projects that investigate the impact of energy improvements in houses, including Innovate UK’s Retrofit for the Future programme. This detailed the energy upgrade of 40 houses, showcasing what did and did not work well. Such guidance is informative and useful to a point, but it was important to the Housing Executive to gain first-hand experience and knowledge through delivering a scheme in-house and to test the local market for energy-related skills, products and materials.
There are different levels of retrofit standards available, from the minimum requirements of the Building Regulations to the Passivhaus retrofit standard, EnerPHit. With such a broad range of performance targets, it was imperative to understand how far we needed to go and how much it would cost. This became the premise for the scheme and led to an intricately designed experiment to improve each house to a different level, to test the practicalities of each option against the cost and the improvements made.
The site in Newry was identified early on in the process as the pilot resonated with the Council’s plans for a Newry Sustainable Zone at the time. The terrace of five three-bed, two-storey houses were perfect for comparison purposes and maintained long term tenants for the most part. Throughout the process there were regular engagement sessions held, to gain a better understanding of the pre-retrofit performance beyond what the energy performance certificates could tell. The project was developed with experts such as MosArt, Passive Haus architects, and the Buildings Research Establishment, BRE. Also, Bryson Energy provided funding for one property that was privately owned, allowing a continuous external wall insulation and render system around the houses.
The project encountered many challenges, mainly in relation to funding, and also the fact that technology was moving on so quickly. It was difficult to pin down exactly what measures, techniques, materials or products should be trialled. This led to a complex matrix of work packages, tailored to each house to meet the desired energy target, which worked well for the most part, though the small tweaks from one house to the next could lead to confusion on-site. An important lesson learned from this scheme was that it is possible to have too much variation in one pilot scheme, and a more reserved approach to test one or two concepts would give clearer results. However, in a technical sense, there were a lot of excellent learning points to emerge, that have informed the Housing Executive in how to implement quality retrofit within a more manageable budget. In particular, the intricate design of alternative details addressing typical thermal bridges such as around openings and at eaves level provided the organisation with a set of thermally robust construction details that could be implemented across the majority of its stock.
Increase in the number of comfortable days, defined in terms of temperature (18°-21°) and relative humidity (40%-70%).
Decrease in heat loss by 45%.
Decrease in air permeability to an average of 5 m³/h/m² from 15-22 m³/h/m².
Decrease in CO2 emissions by 50%.