Insulation helps prevent unwanted heat gain in summer and heat loss in winter. This blanket of insulation requires thick insulation in the floor, walls and ceiling. The amount of insulation required depends on your climate, for example, a house in Auckland will not require as much insulation as a house in Dunedin. A house in the Wairarapa, for example, has to strike a happy medium for the frosty winters and searing heat of summer.
Airtightness helps control the heat and cool air entering the building. Eliminating draughts creates a healthier home and means less heating required in winter and cooling in summer. Airtightness can be achieved by sealing all joints in the building envelope and ensuring windows are properly installed. The use of products such as Pro Clima is approved for Passive House for use in New Zealand. A blower door test can tell you just how airtight your building is. Airtight means you can control your climate (this is continued further on).
Window and doors need to be triple glazed, with the option of Low E and filled with Argon gas (depending on the climate, it could be double glazed at the top of the North Island). This means that hot or cool air within the home is not lost through the windows, which have a lower R rating (insulation value) than the walls. There are other more important elements of windows, but these can be explored later. The placement of these windows is important for the climate the house is in and how much solar gain is required, as too much leads to overheating in summer.
Thermal bridges must be eliminated or lessened in a passive house. Thermal bridging is most common in aluminium windows, so thermally broken windows are required, timber or UPVC is the choice here. The edge of a slab foundation and corners of the wall framing all need to be accounted for. Continuous insulation helps prevent thermal bridging.
The final main principle is Heat Recovery Ventilation (HRV)
With an airtight building, airflow must be introduced using mechanical means. Think of an HRV as the lungs of the house. An HRV system takes out the stale air and replaces it with fresh air. So as to not lose all the heat you have created in winter, an HRV system encompasses a heat exchanger. This heats the fresh air to the same temperature as the warm stale air you are expelling so as to not create a temperature drop within the home. (depending on the heat recovery capability of the unit).
Certified Passive Houses are known for their super low energy use, thanks to their super insulation, airtightness, and build quality.
For my own Passive house, we will be adding solar panels and rainwater harvesting to become more renewable.
What materials to use is a huge factor in sustainable design, as well as the actual design itself.
My belief is that sustainable design should be looked at from a multi-angle approach. As well as considering sustainable materials, the design layout etc, the user is the most important factor. If the user for a home renovation or new build is planning on selling the home within a few years, this does not mean that they don’t need to invest in the sustainable options.
Consideration must be made for the potential new owner on the basis of setting them up with a healthy, well constructed and sustainable home.
Every renovated or new home should be healthy to inhabit, warm in winter and cool in summer, damp and mould free and able to withstand our changing demands, families, environment and climate.
This can be achieved in part by choosing sustainable materials that can help the renovated or newly built home last a lifetime.
Sustainable Design Approach
For sustainable materials consider the products origins, use, life span and end of life disposal.
Some products may not be recyclable at the end of their life and can only be landfilled or burnt, but if they last twice as long as other products, this needs to be considered. Some products may last twice as long as others, but are extracted from an unmonitored questionable source and are therefore unsustainable.
Where did the material come from?
The shortest distance from where the item is to your home (to complete its lifespan) the better.
How is the material extracted? Is it a by-product of other processes? Does it create a useless by-product that can only be disposed of? Is the extraction process environmentally damaging? Does it involve mining? Is it a renewable resource? Does the sourcing of these materials impact any native inhabitants such as native flora and fauna?
Let’s take NZ timber as an example. Trees are fantastic to absorb the carbon humans emit and they are a renewable resource as we replant when we chop down. With Radiata Pine and Douglas-fir grown and processed locally the carbon footprint is low, making this a sustainable choice in NZ.
Things to look at here is if it is FSC certified.
“In order to be given FSC certification, a forest must be managed in an environmentally appropriate, socially beneficial and economically viable manner.” (Source FSC UK website page)
If the material has to sustain a heavy production period which includes machinery, water and electricity to run, the carbon footprint of this material could already be high before its even gone anywhere.
For example; Trees felled on a large plantation require human operated machinery to cut, to strip branches, then to lift onto the trucks. The trucks then travel long distances to get it toward the next phase.
Wool requires raising the animal, herding, shearing, sorting, baling and transport before manufacture can begin.
Man-made materials such as plastics and polystyrene require a very lengthy process.
This is then turning the processed raw material into useable goods. So they need to be trucked/shipped to the manufacturer.
This is where machinery and chemicals can be used to create a final product. Mixing materials to make a composite product can also happen, such as composite decking, wool blend carpets etc. More about this (and why you shouldn’t use it) in another post.
For example; The felled and stripped trees will then be cut into blanks for many different purposes. These are then chemically treated to different levels (if required) to be fit for purpose for a building. Some of the by-products of timber manufacturing and processing are shavings and dust. This is used to create products like chipboard and MDF. A lot of NZ timber is exported. Accoya ships NZ timber to the Netherlands to be treated, to then come back to be sold as non-toxic and very durable timber. (There is a specific, but a lengthy reason for this though)
This phase sees the products transported to the retail store to be sold to consumers. Depending on the retailer, the products will likely need to be delivered to the building or project site.
This phase also includes the construction/installation of the materials. For example; assembling the timber framing for housing, installing carpet or flooring, assembling all the individual products to make a kitchen etc.
There is always excess in this process and a consideration to make is what does the retail store or supplier do with excess materials that aren’t sold? Or, as the consumer, what do you do with the leftovers from your project?
This is where we (the consumer) get to use the product. This could be anything from the insulation in our walls to the flooring beneath our feet. What is very important about this section is: How long is its lifespan?
Since humans found faster and cheaper ways to process and manufacture products, we have developed a throwaway society. This could be where we rip up a perfectly good carpet in a newly bought home simply because we don’t like the colour or feel of it. As they are mostly composite materials, most people are likely to throw this in a skip. Which ends up in a landfill.
Lifespan should be considered from a few perspectives and questions should be asked of each material that will be in use.
Is it versatile? Can it adapt to change of owners, style or primary purpose?
How long is it expected to last? What are the manufacturers guarantees? If it breaks or fails, can I simply repair it?
Is it made from man-made (and therefore mostly landfill-bound) materials? Or is it natural and therefore biodegradable materials? Can it be reused in other ways if it is no longer fit for purpose?
Just as important as the lifespan, is its disposal. Nothing lasts forever, and it will eventually need to be disposed of. The question is then, how does this material have to be disposed of? Can it be recycled?
Old Pink Batts or insulfluff in a houses ceiling does not need to be removed, instead, you can lay new insulation over the top. Its a case of the more the merrier. This will actually increase thermal efficiency when installed correctly. Where this fails is if a now deemed unsafe insulation was originally used.
Old carpet that’s threadbare (think the florally patterned stuff from the ’40s to ’70s) is hard to get rid of. However, people planting trees like to use carpet or old underlay at their base to keep the roots moist. Perhaps donating to a community garden is an option.
Unfortunately, when it comes to renovating older homes, there are lots of materials that have no other option than to be landfilled.
Linoleum, hardboard (used on the walls in wet areas until the early ’80s), fibrous plaster ceilings, old electrical cabling and some plumbing pipework. Materials like these have to be destroyed to be removed from the house, as they don’t come out cleanly. Therefore, they are mostly landfill-bound.
In upcoming posts, we will look at common building materials and the sustainable options for each.
Reason for the examples of timber being used: Timber is one of the most sustainable building materials available. As it is a renewable resource and is a natural and local material. It has many diverse uses and has a good end of life disposal options. Every build in NZ contains some form of timber and sustainable options are easily available here.
In Green Perspective Design Studios practice we like to reuse the materials in renovations where possible. This helps divert waste from landfill and ultimately save money and resources.
This isn’t always easy and sacrifices can be made. Eg: insulating existing exterior walls may involve ripping off old gib to then insulate and replace with new gib. Blown in insulation has not been tested long enough for settling.
Each component of a renovation is looked at in a way that will ultimately extend the buildings life, and therefore its purpose. As well as providing a safer and healthier home, for any and all of its occupants in its revitalised new lifespan.