Want to know how to choose appropriate insulation for your home when renovating or building new?

More insulation isn’t automatically better, but there are ways to determine what to invest in for the best outcome.

Learn what to specify for your ceiling, walls and floor, and what to ask your team so your insulation performs as intended.

Listen to the episode now.

Hello! This is Episode 423, and Way #23 of the 44 Ways to Create Your Sustainable Home series here on the podcast. We’re continuing through Section Five: The Building Envelope.

Over the past few episodes, we’ve covered airtightness, window selection, and how to choose the right building wrap for your climate. 

This episode is about insulation: the various types and what to know about how it works.

Way #23 is: Choose Appropriate Insulation.

Insulation has been part of home construction for decades, and as energy efficiency benchmarks have become part of building and renovating, insulation has been adopted as a worthwhile investment to help reduce the cost of heating and cooling homes. 

But how much insulation do you really need? And where, and what type?

In summer, heat moves in from outside of a home; in winter, it moves from inside to outside. Insulation reduces the transfer of heat through the building envelope. 

Good insulation slows that movement, reducing the work your artificial heating and cooling systems need to do to maintain a comfortable temperature in your home.

Citing the Australian Government resource, Your Home: winter heat losses through an uninsulated ceiling and roof can be 25% to 35%. Your walls are 15% to 20%, and the floor can be 10% to 20%. Summer heat gains are simply those same figures, but in reverse. 

Insulation buffers that heat gain and loss, and depending on where you’re located and the amount of insulation you include, it can reduce your heating and cooling costs by 40% to 50%.

There are two main categories: bulk insulation and reflective insulation, and then you can also have composites of both. 

Bulk insulation works by trapping air within its structure. Those air pockets resist the conduction of heat. It can come as loose fill, batts or panels, or rigid boards. 

Reflective insulation works by reflecting radiant heat away from the foil surface, and it performs best when there is an air gap next to the shiny side. 

Composite insulation combines both, and Anticon is an example of this type.

The common metric to measure the performance of insulation is the R-value: the measure of thermal resistance, or how much a material resists heat flow. A higher R-value means better performance. 

You’ll encounter two types: the material R-value (the performance of the insulation product itself), and the total R-value of the assembly (which includes the insulation, any air gaps, surface resistances and the thermal contribution of other materials in the wall, ceiling or floor).

Each country calculates R-values based on temperatures typical to its climates, so they are not directly comparable. R-values in Australia are metric, whereas R-values in the USA are not measured this way. 

Building regulations in most locations will set out minimum R-values based on your climate and the home’s required performance. In Australia, the National Construction Code sets minimum total R-values for ceilings, walls and floors by climate zone.

The ceiling plane is where insulation typically has the greatest impact. Installing roof and ceiling insulation can save up to 45% on heating and cooling costs. 

If you need a high ceiling R-value, specify a single thick batt designed for that rating, or a rigid board product that holds its form permanently. 

Layering two flexible batts on top of each other can quietly reduce their effectiveness as the upper batt compresses the lower one over time.

In a standard timber-framed wall, insulation is installed in the stud cavities between the internal lining and the external building wrap. In high-performance homes, it’s becoming more common to build walls from a 140mm stud frame, instead of a 90mm stud frame, so it can accommodate a thicker insulation batt for higher R-value performance. 

Thermal bridging through the framing (especially steel frame or structural steel) will reduce the benefits insulation is providing, so external insulation, such as a continuous rigid board fixed over the outside of the frame, can be used to eliminate that bridging.

Floor insulation is less often discussed than ceiling and wall, but as I talked about back in Way #20, Episode 420 with thermal mass, it’s increasingly a consideration to isolate a slab-on-ground from the impact of the ground temperature. 

Slab edge and under-slab insulation are common in Passive House and high-performance construction. 

On a suspended timber floor, insulation is installed in the joist cavities below the floor deck, and access for retrofit is worth thinking about early.

Natural fibre options are increasingly available…such as sheep’s wool, hemp, cotton, cellulose from recycled paper, and recycled textiles. 

One product worth specific mention is wood fibre insulation board: rigid and dense, holding its form permanently, with a thermal mass effect and the ability to buffer moisture in the wall assembly. It’s also fire resistant, which a friend of mine recently experienced when a faulty solar panel sparked a fire on their roof and the wood fibre panels contained it there.

In this Episode, I cover:

• Why insulation matters, and the amount of heat gain and loss through an uninsulated ceiling, walls and floor
• The two main categories of insulation (bulk and reflective) and where composite products like Anticon fit
• How R-value works, the difference between material and total R-value, and why R-values from the USA and Australia aren’t directly comparable
• Why the ceiling plane is where insulation has the greatest impact, and why layering two flexible batts is counterproductive
• Why dark roofs are worth reconsidering in most Australian climates, and their contribution to the urban heat island effect
• Wall insulation, thicker stud frames for high-performance homes, and how to deal with thermal bridging through steel or timber framing
• Slab edge, under-slab and over-slab insulation, plus how to think about insulating a suspended timber floor
• Where spray-in insulation fits, closed-cell vs open-cell, and why it’s still not a mainstream complete solution in Australia
• Natural fibre and low-tox options, including sheep’s wool, hemp, cellulose, recycled textiles (Upparel), and wood fibre panels
• How to model your insulation choices in your energy assessment so you know where the point of diminishing returns actually sits
• The questions to ask your designer or architect and builder so the insulation you specified is what actually gets installed

Plus a whole lot more.

LISTEN TO THE EPISODE NOW.

RESOURCES:

Episode 415 >>> 44 Ways #15: Use Energy Modelling During the Design Phase

Episode 416 >>> 44 Ways #16: Use Other Options to Model Your Design Before You Build

Episode 422 >>> 44 Ways #22: Review Building Wraps to Manage Moisture for Climate

Episode 208 with Sid Thoo >>> Roof Colour: Dark vs Light (and your home’s energy efficiency)

Episode 234 with James Cornell, Life Panels >>> Building Healthier Homes

Episode 235 with James Cornell, Life Panels >>> Moisture Control in Your Home’s Construction

Episode 236 with James Cornell, Life Panels >>> Home Insulation and Wood Fibre Products

Episode 333 with UPPAREL >>> Textile recycling for your renovation or new build

Matt Risinger, Build Show, on the hype versus reality of spray foam insulation >>> Spray Foam Insulation Hype vs Reality

Australian Government’s sustainable design guide on insulation >>> Your Home: Insulation

Industry body for insulation manufacturers and installers >>> Australian Insulation Association

A free guide to simplifying sustainability across research, planning, design, materials, and building, from Amelia Lee’s 30+ years in residential design and construction >>> 44 Ways to Create a Sustainable Home

Access the support and guidance you need to be confident and empowered when renovating and building your family home inside my signature online program >>> HOME Method