Home Insulation Questions Frequently Asked Questions

Click on the questions below to find out more about insulation and it’s benefits. If you cannot find the answer below

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What is the R value?

The R-value explains how well a particular product can perform. It measures the abilities of insulation material by industry standards. This means that the bigger the R-value, the more the product can withstand the transfer of heat energy. This has become more important as the health benefits of good quality insulation have been better recognized.

There are minimum requirements measured in R-value that need to be met and they fluctuate depending on where in New Zealand you live. It also depends on what materials your home is constructed of.

Why should I insulate my home?

Insulating your home is one of the smartest investments you can make. This is briefly described below.

Insulation keeps your home warmer in winter, cooler in summer, and will lower your energy costs. Without insulation or an ineffective amount of insulation, your home will lose heat through the walls, ceilings, and floors.

If your home was built before or during the 1970s, it is highly unlikely that you have any insulation at all.

There are health benefits to having insulation as well. The dampness in the air is diminished by the insulation, thus improving the quality of the air you and your family are breathing in. This is beneficial for the treatment of asthma and other respiratory illnesses.

Having adequate insulation also decrease your power bill.

How long will it last?

We only use/sell products that carry excellent warranties.  Products that have been BRANZ appraised have a 50-year durability rating.  Foil products are shorter in life than other insulation materials as their performance can be reduced by dust which reduces reflectivity. Green Dog Insulation does not deal specifically with foil products, however, we are happy to fix or replace foil for your home if you request this. Generally speaking you can expect with modern products such as Terra Lana wool insulation, that they will last the lifetime of your home.

What does BRANZ stand for and what is it all about?

Building Research Association of New Zealand (BRANZ), BRANZ is an independent and impartial research, testing, consulting, and information company providing ongoing services and resources for the building industry.
Our two main areas of activity are to:
• Research and investigate the sound construction and design of buildings that affect the built environment in New Zealand
• Enable knowledge gained from research within BRANZ to be widely distributed and taught throughout the commercial and construction industry.

BRANZ's core purpose is to improve people's lives through our research and to inform, educate and motivate those who shape the built environment.

How much will I save a year on heating costs?

This does depend on how much your monthly heating bills are, but generally a house which is going from no insulation to becoming fully insulated, could be saving up to 60% of your heating bill. A well-insulated house should save you around $400 -$500 per year.

How is wool insulation different to polyester insulation?

Wool “breathes” as it absorbs and desorbs the moisture within the home. It helps remove the damp chill in older homes and reduces condensation and mould in damp environments (kitchens, bathrooms).  The amazing thing is the water molecules are held inside the fibre, leaving the insulation dry to touch. Inert mineral and synthetic fibres do not have this property and therefore do not handle rapid changes in temperature and moisture nearly as well. This means they are damp to the touch as the moisture is retained within it.

Do rats and mice nest in it?

Rats and mice will nest in anything: Wool, polyester, fiberglass, cellulose. This is hard to avoid. However, vermin will not eat Terra Lana because their teeth cannot cut through the wool fibres, which then get stuck in their throat. Vermin can, and do, chew fibreglass down to a powder and swallow it.

What’s the difference between Terra Lana (wool) and Pink Batts?

The heating ability of equal R rated products is the same. For example, R2.6 Terra Lana has the same thermal resistance as R2.6 Pink Batts. Terra Lana has an initial higher expense than Pink Batts of around 20%, however, the increase in price has large advantages. These are as follows:

  1. Environmentally Sustainable – Wool is one of New Zealand’s most sustainable natural resources. The wool Terra Lana use is either low-grade virgin wool or recycled waste wool from local textile and carpet manufacturers.  Sheep wool is completely biodegradable and can be composted without causing harm to the environment. Even the melt bond fiber which holds the insulation together decomposes safely without emitting toxic substances.
  2. Longer lasting - the wool is combined with a small amount of melt bond polyester fiber and passed through an oven. The heat melts the polyester which diffuses throughout the batting, causing tiny outer scales that hook the fibers together. As the insulation comes out of the oven the melt bond fiber cools, setting the height of the insulation. The natural crimp or ‘springiness’ of the wool fibre plus the resilience of the polyester mean the insulation will maintain it’s height for a long time (BRANZ appraised for 50 years) and therefore its ability to entrap air. By contrast, the glass fibers in fiberglass insulation break down over time when subject to movement or vibrations, (such as earthquakes) causing the insulation to slump, reducing its effectiveness.
  3. Naturally Healthy - Wool is a protein fiber similar in structure to human hair so even if wool fibers are ingested or inhaled they readily break down into their base proteins and cause no harm. This means that no protective clothing or gloves are required when installing Terra Lana. Fiberglass is literally that, fibers made up of fine filaments of glass.  If ingested, these can aggravate the respiratory system. Due to these issues, protective clothing, gloves, and face masks are required to reduce the effects of the fiberglass on the skin and respiratory system.
How much insulation should be installed?

The amount of insulation a home should have will vary, depending on where it is located and how it was built. The amount varies depending on the three areas of your home in which you insulate.

  • Ceiling - your ceiling insulation should sit between the ceiling joists. If you have downlights, they should be I.C rated. If not I.C rated, you MUST clear a space around them to avoid a fire risk. See more at downlights.
  • Underfloor- insulation needs to be stapled
  • Wall - the wall cavity needs to have building paper in place against the outside wall. R 2.6 and R 2.8 require 90mm cavity. R 3.2, 3.6 and R 4.1 require 140mm cavity.
What sort of disruption will there be to my home?

Most installation jobs will be completed in less than a day, but the answer really depends on the size of your home. We will notify you of the expected length of time when we book in your job.

What is involved in installing under floor insulation?

Under floor insulation is installed between the flooring joists from underneath the house. It is not invasive and does not require the home owner to do anything. A minimum ground clearance of around 450mm is required in order to gain access under the house.

What is involved in installing ceiling insulation?

In order to get into the ceiling, we need to have an access hatch somewhere in the house. Often these are located in hallways, washrooms, or bedroom closets. There are generally two forms in which we install insulation - batts/nugget form which is inserted between the beams, and blanket form that is laid over the trusses or rafters.  This is the optimum way to install insulation and minimize heat lost out of the house.

For houses with skillion roofs (sloping ceilings with a small gap between the ceiling lining and roofing material) or exposed rafters, we can supply and install a special insulation blanket that is specially designed to fit into these types of roofs.

How do I know what you're installing is safe?

We only quote, supply and install products that are BRANZ tested from reputable manufacturers. All of our installers are security checked and have been properly trained and accredited in installing insulation correctly and safely.

Why should I replace my down lights?

If your house has old downlights, then you might want to consider replacing them with newer downlights with either CFL or LED light bulbs.

Old downlights are a fire risk, allow cool air to move into your house, and allow dust from the roof to be blown into the house as they are not sealed units. Having downlights that require a 150mm safety clearance reduces the effectiveness of your ceiling insulation by up to 50%, but this is necessary to keep you and your family safe.

By contrast, there are now available modern downlights that are rated for insulation to be laid right up against them as they are not a heat risk and that are sealed units so that the air in your roof space cannot pass down into your home.

Replacing your downlights with energy-efficient units that allow insulation to be placed right up to them will dramatically increase the effectiveness of your insulation and will produce very large savings on energy costs paying off the cost in as short as a couple of years.

When should I install insulation?

The most economical time to install insulation is during construction of new buildings and during renovations before walls, floors, and ceiling spaces are closed in. However, it's also common (and cost-effective) to install insulation or upgrade insulation in existing homes.  (Smarter Homes website www.smarterhomes.org.nz)

Where should I install insulation?

Most heat is lost through the ceiling so that should be your top priority for insulation.

The design and construction of your home will affect the specific types of insulation you can use, and where the insulation can be placed.

With some construction systems - such as aerated concrete blocks, glass blocks and straw bales - little or no additional insulation may be required.

Roof and ceiling insulation
Roofs and ceilings work most effectively if they are insulated together. About 42% of heat loss from an average uninsulated home occurs through this area (up to 60% in older houses).

Wall insulation
About 24% of heat from an average uninsulated home is lost through the walls. Wall insulation can double as a moisture barrier.

If you're using a framed construction system, insulation should be placed within the wall framing. Insulation can also be installed outside the framing (but the insulation must be weatherproof to be effective).

Note that the amount of insulation you can install may depend on the thickness of the walls and the size of the framing. If you're building a new home or renovation, consider increasing the framing size to fit in more insulation.

If you're using a solid construction system such as concrete, insulation should be placed on the outside of the solid wall. The inside of the wall can also be insulated.

Wall insulation can be fitted to existing homes by:

  • Removing wall claddings and installing blanket or biscuit insulation - this is the best option for timber frames
  • Pumping or 'blowing? bulk loose-fill or foam insulation into the top of the wall cavity, or through holes in the top of an external wall - this can be done for timber frames, but is labour-intensive and difficult to get a consistent fill
  • Fixing solid or blanket insulation to the outside of solid walls - this will include external cladding as part of the system.

Floor insulation
Up to 20% of heat loss occurs through the floor of uninsulated houses. Insulation should be used:

  • on the underside of suspended timber or concrete floors
  • on the edge and underside of concrete floor slabs.

In existing homes, depending on access, you can fit:

  • foil and/or bulk insulation beneath suspended timber or concrete floors
  • Insulation around the edge of a concrete slab.

WARNING: Installing underfloor foil insulation can be risky.  Be careful not to pierce electrical cabling with staples.  Existing foil insulation, if improperly installed, can be live.  If you are unsure about anything, hire a professional installer or get an electrician to check things out.

What are the benefits of insulating my home?

Improved thermal comfort all year round:
Insulation keeps warm air within your home during winter and slows the flow of heat into your home in summer. This means you have more comfortable temperatures in your home all year round.

Reduction in noise levels:
Insulation is a great sound absorber and can assist in reducing noise in between rooms and floors or your home. This makes for more quiet environments in your home.

Save on your energy costs:
Did you know that BRANZ research has shown that installing insulation in your ceiling alone into an uninsulated home, it would pay itself back over 4 years? This means that over 20 years it would have provided a net benefit of $3000. (Based on a 150m² home).

Helping the environment:
Insulation is a way to help reduce the consumption of fossil fuels, such as coal, petroleum, and natural gases, which are adding to the Green House Effect. Wool insulation is also an environmentally sustainable type of insulation which is derived from recycled wool.

Insulation controls condensation:
Insulation brings the air temperature above dew level to help stop the formation of condensation. Wool insulation also wicks away moisture keeping your home dry.

Bringing insulation to the people...


This week I've had Terra Lana insulation installed in the ceiling and underfloor at my home. I'm writing to advise you that Pm well pleased with the work of your employees, Jon, Andy & Nathan.



I am in my sixties and I have a warm open plan living-dining room and kitchen area. Since the insulation has been installed, this now keeps me warm even on the coldest of winter nights with just 1200watts oil fin electric heater. Last winter it took me 2200watts of the same heating source to heat that area, so I am very pleased.



We were very happy with your service, from the first phone call I made to you through to the assessment and the installers of our new insulation and the guy who came to check it all out. Top marks to all of you. And yes, we have noticed a difference, our living area holds the heat better, even with our cursed 14 downlights.

Neil & Doreen