Insulation (What product best suits my project?)

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Why should I install insulation?

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Effective home insulation can reduce heat losses and your heating bill by up to 50%.

It is a requirement in new homes! 

NZBC Acceptable Solution H1/AS1 effective 31 October 2007 specifies minimum insulation requirements for residential buildings You will save money on heating by using less energy and getting the best efficiency from your heating system.

Heat is lost when the outside temperature is lower than the inside. In an un-insulated house typical heat loss is: 42% through the ceiiing, 24% through the walIs, 12% through windows, 10% through floors and 12% through ventilation (poorly sealed doors, windows).

Installing insulation when building is logical – it’s cheaper to install during construction.  Remember, a good insulation product will not only keep you warm during the winter but will also keep your home cool during the summer by reducing heat outside getting into your home.

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 What is best?insulation_install.jpg

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The best insulation is a cocoon that wraps the house in a ‘thermal envelope’.  The ceiling, walIs, windows and floor form a protective surround.  Insulation materials are given R-values, a measure of their resistance to transfer heat. The regulations require a mean thermal envelope R-value of R1.5.   The higher the R-value the better the insulation effect.  Remember most heat is lost upward through the ceiling.  Here is where the greatest R-value insulation gives the best returns! Recommended thermal ratings above the minimum code for a comfortable home environment include R2.2 for ceilings, R1.8 for walIs and R1.5 for under floors. Insulation must be fixed thoroughly with no edge gaps to allow heat to escape.  A 10mm gap can Iose up to 50% of your heat.

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Which product should I use?

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Insulation comes in many forrns and products, blanket rolls, segment blocks or pads, loose fill, sheets, polystyrene, rockwool, glass wool, cellulose loose fill, polyester or wool/polyester mix, or basically wool alone.

Some thermal insulation products can supply acoustic insulation at the same time, especially useful for filtering out unwanted noise from either outside your home or between rooms. Ask for endorsing information on this from the insulation supplier.

Check the benefis and features, cost and performance efficiency (R-value).  You want a product known to last (durability of 50+ years). Choose a product that has a BRANZ Appraisal (Building Research Association of NZ ), not just a BRANZ test, this ensures you are getting an approved / credible insulation product.

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Ease of handling and insulation

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Natural or man-made?  Will it burn, resist vermin, mould and rodents? Is it corrosive to pipes and electrical wiring?  Does it have acoustic absorption properties to help reduce household noise?

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Thermal Bridging 

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A thermal bridge in a building occurs wherever poor insulating materials (such as framing) within the wall run from the warm side to the cold side of the wall. This means that heat has an easy path to travel from the inside of the building to the outside – much the same as picking up a hot pot off the stove with a wet cloth (poor insulator) the heat will travel easily from the pot to your hand through the cloth. 


Typically poorly insulated framing makes up around 25% of traditional framed walls in New Zealand and takes up space which cavity insulation cannot be inserted. This significantly reduces the overall thermal performance of the wall regardless of how good the cavity insulation is.

  •  A warmer wall means there is less potential for water vapour in the air to reach its dew point, which means less potential for mould
  • Cold surfaces are the major cause of condensation, if you have a warmer surface on a wall then you are less likely to have condensation on that surface. Exterior insulated sheathing is a good way to keep the entire wall frame warmer so that when the water vapour in the house is trying to move toward the outside (as it does when its colder outside) there are no cold surfaces to trigger condenstation.  Reduct condensation and you are less likely to have mould probelms.

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 Useful Tips to Remember

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1. The higher the R value the better the insulation.
2. Insulation must be installed without gaps to give its full benefit.  Once the wall linings go on it’s difficult and expensive to change things – do it rıght first time.
3. Insulation is bulky and awkward to transport; make sure you ask for a delivered-to-site-price.
4. If noise irritates you ask about acoustic absorption insulation between living and sleeping areas or upper and fower floors.
5. You may also want to insulate your hot water cylinder, especially if it is an older one.
6. Most heat, approximately 42%, goes out through the ceiling which is normally accessible and gives very good returns once insulated.