The Parka Wrap: Retrofitting insulation onto the existing walls of occupied homes

Abstract

RESEARCH QUESTION Are there safer, more effective ways of improving wall thermal performance while limiting occupant disruption?

RESEARCH AIM Design new retrofit methodology where insulation is overlaid on an existing wall.

ABSTRACT

Currently, there is limited research to improve an estimated 830,000 homes in New Zealand that have no insulation within the external walls. Unfortunately, there is no comprehensive policy, standard or best practice guideline to housing providers and homeowners for retrofitting external walls that are not insulated. Therefore, this research aims to understand how practitioners can design and implement building interventions over existing wall claddings to increase thermal performance in existing occupied as-built homes.

While retrofitting homes have underlying barriers to implementation, the research will primarily focus on application technique and practical knowledge while considering thermal and hygrothermal performance. Aspects of construction and social costs will be acknowledged within the research but is out of scope.

The thesis is divided into seven chapters. Chapters one and two outline the research purpose and define the research question. They are followed by review of key background literature in chapter three and case studies within the subject field in chapter four. These lead to the evaluation of testing methodologies and the design of experiments in the fifth chapter which also describes the software simulations of proposed materials and assemblies.

Chapter six describes actively tested iterative scaled sections of building walls within a controlled environment. The knowledge gained from scaled testing is analysed and applied to a typical New Zealand bungalow wall and tested with wind, water and seismic pressures to provide insight into the process of retrofitting homes. The final chapter will review the value of the research and conclude with next steps.

International research and practice show an existing building’s walls can be retrofitted externally. In New Zealand, cold houses cost New Zealand $7 Billion annually in respiratory healthcare, however there are major knowledge gaps in how to retrofit to create thermally efficient homes without causing harm to the building’s durability. Case studies of attempted improvements using external insulation suggest it can easily result in a negative outcome with building damage (moisture entrapment) when available building science is ignored or misunderstood. Precedents internationally have suggested positive outcomes when the insulation has been applied as an external blanket; however, specific material combinations are critical to this success or failure.

Modelling the implementation of the proposed Parka Wrap system to existing buildings shows a 60% reduction of energy required to maintain 20 degrees inside a typical house where insulation already exists in floor and ceiling. Physically testing existing walls pre-retrofit shows they are leaky for both air and water as water is driven through existing cladding by wind pressure. The effects of wind alone contributes to cold internal environments. The addition of water requires either drainage and/or significant drying potential to avoid damage to structural framing. The subsequent physical testing for water penetration in NZS4284:2008 test rig included seismic racking, and repeated water penetration testing has shown evidence of successful development of a robust weathertight assembly with predictable thermal performance. Further software based analysis of proposed design ensures avoidance of predictable moisture accumulation.