Insulation and R-Values
Insulation
Insulation is a material that slows or stops the transfer of heat with the aim of keeping a building warm in winter and cool in summer.
Insulation needs to be continuous to be effective. Even 5% gaps in insulation can reduce its effectiveness by half. (Edwards, 2018)
The ceiling or roof is the home’s weakest point, losing the most heat in winter and allowing in the most heat during summer. The ceiling should be the priority for insulation, followed by the walls and then the floor.
The following are the most common types of insulation:
Batts – A form of bulk insulation made from wool, glass wool or polyester, easily installed in structural framing.
Loose-fill – Small polystyrene blocks or loose-fill fibre that can be pumped into wall cavities.
Foam – A dense board product used for smaller spaces. Certain types of foam board can be used as insulation underneath and at the edges of concrete slabs. Spray foam is also available and is applied as a wet spray that rapidly expands and hardens.
Reflective – Unlike the products above that rely on small air cavities to create an insulating effect, reflective insulation has a shiny surface that reflects radiant heat.
R-Values
A material’s insulating effectiveness is measured by an R-value, which is a measurement of resistance to heat flow. A higher R-value equals better performing insulation. The Building Code of Australia sets out minimum insulation requirements for the climate in which you’re working.
Higher R-value batts will be thicker. For example, a typical timber stud wall can fit 90 mm insulation batts valued at R2.5. In the ceiling, where more space is usually available, an R5.0 batt will fit in a 240 mm-wide space. Comparatively, an R3.0 batt is often 130 mm wide or an R3.0 polystyrene board is 85 mm. (Milne et. al., 2013)
Note that R-values in the United States aren’t measured in standard international units. American R6.0 is equal to Australian R1.1.
A typical brick veneer wall with R2.0 batts and plasterboard lining will have a total system R-value of 2.24.
Working with a collaborative NatHERS energy-assessor will help you optimise the R-values depending on your project, climate and budget, and avoid diminishing returns. We work with an energy-assessor on every project as a non-negotiable.
Where to find more
The information above is extracted from my book, 101 Things I Didn't Learn in Architecture School; And wish I'd known before my first job.
While the book is written for students and graduates of architecture, it is also an excellent handbook for anyone embarking on their own project. We provide a free copy with every on-site briefing and feasibility meeting, or you can purchase your own copy here.
My knowledge of this subject comes from years of working under Jenny Edwards, building scientist and Director at Light House Architecture and Science. Her website includes further excellent resources and case studies on this topic. See below for two of Edwards’ articles, referenced above.
Another great resource on basic principles in Australia is the YourHome.gov website which is free to access.
References
Milne, Geoff, Reidy, Chris, and Chris Reardon. 2013. “Building Rating Tools.” Your Home: Australia’s Guide To Environmentally Sustainable Homes. Department of the Environment and Energy. www.yourhome.gov.au/you-begin/building-rating-tools.
Edwards, Jenny. 2018. “Windows 101 – R U Confused.” Light House Architecture & Science. www.lighthouseteam.com.au/journal/windows-101-r-u-confused.
Edwards, Jenny. 2018. “Gaps are No Good.” Light House Architecture & Science. www.lighthouseteam.com.au/journal/gaps-are-no-good.