Rule 3: Insulate, Insulate, Insulate
Houses are, on the whole, fantastic things. They give us all sorts of benefits: Privacy, space to store our stuff and a whole life-support system of services and systems, from hot water to waste disposal..
But one of the main reason we decide to live in houses, rather than bedding down in a swag under a coolibah tree, is the controlled microclimate our houses allow us to achieve.
Face it: It’s hot out there. Or cold. Or windy, snowy, rainy or whatever.
So it makes sense to try to keep the weather we want on the inside, and the weather we don’t want on the outside. But there’s one big problem: our homes leak heat, both inwards and outwards, meaning the inside climate we’ve worked so hard to create is always escaping, and the less-than-ideal outside climate is eternally working its way in. What’s the biggest way to reduce that leaking? Three words: Insulate, insulate, insulate.
Most building codes worldwide now have minimum standards for insulation, and more and more people are retrofitting their existing homes with one sort of insulation or other. We all know that it’s good, and that we should get ourselves some. We have a rough idea that it works something like a blanket, slowing the transfer of heat from a hotter medium to cooler. We know that it helps to keep the outside out, and the inside in.
It should be simple – but it’s not.
A quick trawl of your search engine of choice for information about insulation will reveal a bewildering cornucopia of different types, materials, performances, measurement systems and purposes. The range of products can be bewildering, while differences in measuring insulation can be downright misleading.
Some insulation companies companies measure the thermal resistance of their products by ‘U’ value, most by ‘R’ value. Each measurement means the opposite (A low U-value means a high R-value, and vice versa). To make things even more confusing, R-values are measured differently in metric (kelvin square metres per watt) and imperial (Degrees Farenheit square feet per Btu). (Note: 1K-m2/w = 5.67446 °F-h/Btu). Check carefully when you compare claims for R-values from overseas.
Some insulation companies measure the performance of their product by itself, and some publicise the ‘whole of wall’ or ‘whole of roof’ performance. Check the small print on any manufacturer’s literature for this. And it’s difficult to compare the performance of reflective insulation with bulk, as they work in entirely different ways.
So what do you need to know when insulating your low-energy house?
The first question you need to ask is “How much do I need?”. Statutory R-levels of insulation are usually set by your local Building Code (The BCA in Australia), but you do have to remember that these are minimum levels only. While a higher R-value is normally better, there are exceptions and there are points of diminishing returns. Getting an energy rating performed on your house design by an accredited house energy rater is often a good place to start. Some insulation companies also publish insulation guides for different locations; these can provide worthwhile advice.
The second question you need to ask is “What type of insulation is best for me?”. There are three main types of insulation available. Bulk insulation uses tiny pockets of air, which resist heat flow, and include Glasswool, Polyester, polystyrene boards and the various types of fluffy batts, blankets and blow-ins. Reflective insulation is great for reducing radiant heat transfer, and includes the foils and other shiny things. Composite insulation uses a combination of reflective and bulk insulation, and includes foil-faced boards, blankets and bubblewraps.
To choose the right type of insulation, you need to know what kind of heat it will be resisting; conductive, convective or radiant. Will most heat be moving outwards or inwards? You also need to know where it will be located and what the limitations of that location will be (how will it be installed? What conditions will it be under? Does it need to be fire resistant? Will it get wet? Will it need an air-space? Will it be crushed or moved by other building elements?).
The third question you need to ask is “How will it be installed?”. This is a biggie. As in every aspect of house design, detail is everything. A good insulation system will be worthless -or even dangerous- if badly or inappropriately installed. Ask your insulation supplier for their standard details or installation instructions, and don’t be afraid to change systems if the installation system doesn’t suit your house. Push your Architect/Designer to detail the installation well, and push your installers to do the job properly.
Insulation is, in many ways, the starting point for most low-energy house design. Get this wrong and everything else you achieve will be leaking out your roof and walls from day one.