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To achieve a “healthy home, health living” rating for your home requires an understanding of the elements needed.  Our homes are actually a living environment that becomes the residency for unhealthy and undesirable creatures, if we don’t understand why they are there.  With the correct knowledge and use of the right elements your home will become a “healthy home”.

Understanding Insulation

The importance of insulation is to understand how heat is lost, warm air will always want to go from where it is to where it isn’t. The two main culprits of heat loss are all your cold external surfaces and  infiltration or draughts. Insulating these surfaces considerably reducers your amount of heat loss and energy use. Floors and ceilings are of coarse the first, and in most cases the easiest to do as these two surfaces are mostly accessible. Be careful in choosing the right type of insulation as an R-Value label isn’t necessarily an indicator of the product performance under all conditions. When the weather is at its worst, is when you need that R-Value claim to be working. Next the external walls, once you have insulated the floor and ceiling your next biggest heat loss is the walls and more difficult to achieve (or should i say time consuming) has a higher cost to re establish the walls back to what they where. However the external walls are very significant in the your whole insulation programme and need to be given a serious priority. Benefits are, reducer’s heat loss and eliminates convective wall draughts, this alone is a wonderful benefit.

Insulation Materials

As the demand for insulation increases so does the variety of products, but basically they all fall under the same group of fibre based materials while others are foams (polystyrene's). All made with different types of manufacturing plants and methods according to what the manufacturer is trying to achieve. Some forms of insulation are pure in there fibre content while others include a mixture of other fibres to enhance the performance. Some are chemical free and others have to include chemicals to meet building code requirements. It may seem easy to choose the right product for your application if you are looking at R-Value and cost alone, but in our experience R-Value and cost is a poor indicator of performance or effectiveness especially over the long term. You only want to insulate once so choose carefully.

Insulation Benefits

  • Improved indoor comfort
  • Healthier living environment
  • Savings in energy and health costs
  • Reduced condensation occurrence
  • Reduced risk of mildew growth
  • Lower heat gain in summer
  • Higher durability of internal finishes because of lower moisture levels within the building

Insulation And Lighting

Modern recessed light fittings seriously compromise your ceiling insulation as building code requirements require an insulation clearance around the light fitting. Check you’re fitting’s manufacturer’s specs on the correct procedure and insulation placement. Heat loss and heath aspects are another serious consideration.  Learn More

Where To Insulate?


High levels of ceiling insulation can provide the highest benefit in terms of energy savings. About 40% of heat loss from an uninsulated house is via the roof, due to warm air's tendency to rise. 


Effective under-floor insulation has a great impact on the experienced comfort in a house because a warm floor removes that cold air layer pushing all your heat to the ceiling. If the under-floor insulation material incorporates a vapour barrier, it can prevent ground moisture ingress into the house (rising damp).


Wall insulation levels should be maximized when the building is constructed, as upgrading at a later stage can be expensive or difficult. If you are considering renovating or wish to make any room warmer then insulating your existing walls makes very good sense. We now have a retrofit solution to insulate existing walls without much disruption and leaves most of your jib lining intact.

Call or use our enquiry form for further information.


Ensure your new windows have a high overall thermal performance, which must consider both the frame material and the glazing material in order to provide the true thermal resistance (R-value) of the window. The Windows Efficiency Rating Scheme (WERS) is a four star rating system for windows and is a recommended guide for choosing windows.

Approximate R-Value For Glazing

  Single Glazing Double Glazing Double Glazing with Low E glass
Timber/PVC  0.19  0.36  0.48
Aluminium  0.15  0.26  0.31
Aluminium thermal break  0.17  0.31  0.40

How Insulation Works

Thermal resistance can be provided in two ways:

Bulk insulating materials trap numerous pockets of still air to reduce heat loss from conduction through the structure. Air is a poor heat conductor.

Note: Product installation is critical - Negawatt has developed installation techniques that improve the product performance by up to 25%. Poorly installed insulating materials (e.g. with small gaps around the edges) achieve only 50% of the performance of properly installed insulation.

  • Bulk insulation in walls must be protected against airflow's by an air tight jib layer and a wind barrier (building paper) on the outside of the cavity. If you use high density wall insulation then air movement is eliminated.
  • Bulk insulation must be protected against moisture to insulate effectively. If moisture is allowed to entrer bulk insulation no matter what type it is then the thermal resistance is lowered and becomes less effective. 
  • Some insulation products slump over time, leaving edge gaps between the bulk insulating material and the framing, which reduce the thermal performance by up to 50 percent.

Reflective foil insulation reflect heat radiation to reduce radiated heat loss from the structure. They must be installed facing at least one adjacent, un-ventilated airspace of at least 20 mm width to provide effective insulation.

Note: Product installation is critical - Negawatt has developed installation techniques that improve the product performance by up to 25%.

  • Single aluminium foils often loose their thermal performance within a few years by delaminating and becoming tarnished or corroded. And often severely ripped due to wind exposure and rodents.
  • Thermal performance of foils is reduced to near zero when condensation forms on the reflective surface. This can be prevented by using a reflective insulation product incorporating a heat conduction barrier (e.g. Air-Cell) and by inhibiting moisture ingress into cavities.

What Levels Are Required?

All building construction must comply with the New Zealand Building Code, which requires thermal resistance of the building envelope to avoid fungal growth or the accumulation of contaminants on linings and other building elements (NZBC Clause E3), and to achieve an adequate degree of energy efficiency (NZBC Clause H1).

Your Guide To Smarter Insulation

In respect of energy efficiency, NZS 4218 'Energy Efficiency - Small Building Envelope' sets out minimum requirements for the thermal resistance of building elements for housing and small buildings.

Reflecting climate variation across the country, for the purposes of this standard, New Zealand is divided into three climate zones with Zone 1 being the warmest areas.

The minimum total R-values of NZS 4218, Section 3.1 'Schedule Method' are:

Building thermal envelope component Minimum Total R-values [m2 ºC/W]
Climate Zone 1 Climate Zone 2 Climate Zone 3
Roof / Ceiling R 2.9 R 2.9 R 3.3
Wall R 1.9 R 1.9 R 2.0
Floor R 1.3 R 1.3 R 1.3

If these requirements cannot be met by some building elements, specific thermal building design is required, using calculation methods or computer modeling techniques. Ask Negawatt for advice on ways to achieve the code requirements.

Note that these R-values are minimum standards, and new buildings only providing this level of performance cannot be considered as particularly 'energy efficient'.

Going Beyond The Minimum

Installing higher R-values has proven to be more cost efficient over time and to provide greater overall comfort. Installation costs are the same regardless of the R-value installed, so you gain a proportionately greater benefit for cost incurred through installing a higher R-value.

Negawatt can advise you on the selection of well-balanced insulation levels and window options to improve energy efficiency of houses beyond the minimum requirements of the New Zealand Building Code. Find out more.

Impact of Installation Systems on Insulation Performance

The way insulation is installed impacts greatly on the performance achieved. Once installed the building component is termed as having a system R-value. The product R-Value as stated on the packaging or information pamphlet of the insulation is not necessarily the system R-Value achieved.

For example, the amount of timber in each area of insulation has a considerable effect on the thermal envelope. The reason for this is the high thermal conductivity of timber, allowing faster heat transfer than the insulation and therefore acting as a thermal bridge.

If these areas of differing conductivity are not encapsulated by the insulation then thermal system performance is reduced by the effect of the thermal bridging by up to 25%. If the insulating materials are poorly installed (e.g. with small gaps around the edges), the thermal performance is reduced by another 50%.

The chart below shows R-Value comparison of biscuit and overlay installation techniques for NOVAtherm Polyester Insulation.

  Biscuit R 2.4 Overlaid R 2.4
Description R2.4 Insulation laid between the ceiling joists directly on top of the ceiling lining - known as "batts" R2.4 Insulation laid over the ceiling joists in blankets - like a duvet over the rafters
System Performance R 2.02 R 2.67

Biscuit versus Blanket

Negawatt prides itself on ensuring that you make the right choice and get the best value for money. We do not sell a one-product solution - instead we stock the best products across all areas, and we help you make the best choice. Before jumping in and spending a lot of money, make sure you have the right diagnosis for your home. It's easy to spend a lot of money and be disappointed in the results.

Extremely Alarming Insulation News

If you are building new or have recently built, this government report on home insulation and its standard of installation is extremely alarming. Your new home may be performing well below the building code requirements. Download Here


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