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Insulation Options

Insulating your house is like wearing a winter jacket- it helps you keep the heat inside. This creates comfort and cuts down your heating costs. If you live in an old house, as many do, then you might ask: which part of the house loses how much heat? Renovators are often unsure where insulation is best put to save on heating costs.

If you are building a new property, all walls, roof, and the floor will be insulated, as is the norm today. If you are renting out an older home, then the property needs to be insulated in the roof cavity, stopping heat escaping as well as underfloor, stopping the cold coming inside your home. Where do our homes lose how much heat? According to BRANZ, this is where our houses lose heat.











Please keep in mind that this focuses on existing or more standard homes. High efficiency homes are often different; cooling is often a serious issue and things like thermal bridges (breaks in insulation because of wood framing and so forth) become more important to focus on.


What an R-value really is

The insulation value is measured by the R-Value. The R-Value describes the insulation material's ability to resist heat flow- meaning how good the material is in keeping the heat inside your home in winter and outside your home in summer. The higher the R-Value of your insulation material is, the better it performs. Important to note in R-values that are advertised is that they are stationary R-values. They do not include how materials deal with moisture (in liquid and gas form) or their heat storage capacity. 

While the R-value is important, it is also important to note that the value given by manufacturers depends also on a few things: is the insulation dry? Wet insulation is like wearing wet clothing and does not insulate as well. In time, in nearly all buildings, moisture will pass through the insulation. Some insulation materials can lose in damp and drafty conditions up to 90% of their insulation value.


Is the insulation fluffy or compressed? Insulation that is compressed is less efficient than insulation that is installed with enough room. How thick is my insulation? As a general rule: if the insulation is installed with enough space and dry and the thicker it is the more insulation or R-value it has. Are there gaps around your structural frame, leaving parts exposed?

Will more insulation always save me money?

Very important to note is that more insulation is not always better. The first bit of insulation is the most important. The more we add after that, the less we save from thereafter. Let us imagine for the moment that your current home has no insulation in the walls. Adding 9cm of R2.2 insulation will have a significant impact on energy use and likely save you a few hundred dollars per year. Making out of those 9cm 20cm will also save you money, but not twice as much as the 9cm. In doing the calculations, we sometimes find that adding another 0.5R value barely saves $20 per year, so not necessarily a great investment (this is dependent on wall area compared to roof/ floor area, window area, where the house is located and more- this example does not apply to all homes). It surprises people when we advise them at times that adding more insulation makes little financial sense and they should rather look at other options to save on energy. It is all about balance and making sense.

Does Thermal mass insulate?


In short, yes. Every material insulates to a degree; if you sleep in a tent, then it is already warmer in the tent than under the sky. But thermal mass, as for example, bricks, concrete, timber or earth/ adobe, has additional insulation capabilities: they take the heat during the day from the sun in and then release it again at night slowly, minimizing the heat loss. This capability is in regular R-values not considered as they ignore the effect of the sun energy on the material. Multiple real life studies without occupants; so we cannot blame their behaviour for the changes; show that thermal mass in certain thicknesses and situations outperforms other buildings with a higher stationary R-value. Further, if we take the stationary calculated R-value of those thermal mass buildings, they often should use between 30 and 100% more energy than they actually do. Again the wide range in fault of the calculation is based on the particular situation (how much sun can get onto your walls directly or thanks to reflection) and the thickness of the walls (how much thermal mass and therefore how much energy can be stored). There is a big HOWEVER, it depends on the situation and thickness of the walls!

Also, import when working with high thermal mass walls: Let us say you are planning a rammed earth wall and are curious about the thickness you require. First, as all sides of the home get a different amount of heat on the walls, they will have a different real life R-value which needs to be calculated. Second, different thermal mass materials can store different amounts of energy. Third, color matters: a darker color high thermal mass wall will outperform a light colored one.

If you are curious and want more info or help to calculate the actual heat loss with thermal mass walls, get in touch and we can help you.

Below, we checked out for you different options to insulate your home and stay warmer and more comfortable inside your building. In New Zealand it is now a regulation for all rental properties to have underfloor and roof insulation (2).


(1) Building Performance NZ, 'R-values for common construction types', NZ Ministry of Business, Innovation and Employment,  November 2019

(2) Tenancy Services, 'Current insulation regulations', NZ Ministry of Business, Innovation and Employment, November 2019

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Sheep Wool Insulation

Sheep wool is a fantastic natural insulation material that is renewable and low on carbon emissions in its production. Sheep wool is warm, and the production tends to benefit our local manufacturers.

Straw Bale Insulation

Straw bale insulation is usually a locally sourced, sustainable and renewable product. The insulation value of straw bales is hard to beat.

Cellulose Insulation

Cellulose insulation is often used as a spray in renovations to insulate buildings. Cellulose is mostly recycled paper that is treated for fire and pest resistance.

Rock wool/Glass wool Insulation

Glass wool insulation is the most used insulation in NZ at present. It is easily every building merchant accessible.

Polystyrene & Polyester Insulation

We all know them: polyester from some of our clothes and polystyrene from food containers. But those plastics can also be used for insulation.


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