Why should I build an energy efficient house?
My family and I have lived in a HomeStar 10 house
since 2017. We didn’t set out to build a Homestar 10, that happened along the way, and that’s another story, but we built the house because I had been getting this same question from clients for years and I found it difficult to convince people of the cost/benefit. So we said, right, let’s build an energy efficient house, live in it for three years, get some data and find out what was good, what was ok, and what was a waste of time. After the first year, we gathered some data: Average Temperature throughout the year 21.88 degree, Hottest day, (internally) 27.6 degrees, coldest day 17.8 degree, cost to run, $1498.60. Within the first three weeks, we knew this was something else, when one morning we looked outside and there is a -4 degree frost and inside it was 19 degrees with no heating on. But there was so much more… Health improvements, no colds or flu, you don’t need a summer and winter duvet on the bed, just a summer one, having the same room temperature in every room, you can literally raise the temperature in your home by roasting a chook.
What is Holistic Design?
You can’t pick and choose your energy efficiency. Putting Photovoltaic panels on a code built house does not make it energy efficient. When we start thinking about the home in the terms of energy loss, we start to make critical decisions about the methodology around design and construction of that house or renovation. This is the best way to approach an energy efficient home design. It is when we take into account; the orientation to the sun, wind direction, thermal efficiency of construction, energy use, water use, sustainable materials, construction waste, biophilic connection
, chemical off- gases, acoustics, we develop a healthy sustainable home.
Aren’t all new homes Healthy?
One of the most misunderstood aspects in the construction industry in New Zealand, is the effect on health by our homes and the buildings we work in. If our homes are cold and damp they will breed mould in the walls, cause asthma, and even early death. The World Health Organisation recommends that our home internal temperature doesn’t drop below 18 degrees throughout the year, without being mechanically heated. Yet there are some brand new housing in this country, where the internal temperature is regularly below this. The building code is under review at the moment but this will take years to change.
Doesn’t it cost more to build 'efficient' houses?
Yes, it does cost more to build an energy efficient house, that is over a ‘code built house’. But that’s the whole point. What you need to remember is that the price of electricity increases 100% every decade, and has done since the 1970’s. So, as I tell my clients, you either spend the money on the build, or you spend the money over the lifetime of the build (house) but you will spend the money.
What is a Square Metre Rate?
Thirty years ago when the government changed the building code, they introduced a legal minimum of quality that a new home in New Zealand had to be built too. The idea was, and hoped for, that the industry would use that as a base line and build better. The reality was that the industry saw it as a finish line not a start line. The first thing they did was take an existing plan and price to the building code. If the plan was 100 square metres, say, and cost $95,000 to build (remember the code changed in the 1990’s) it was $950 per square metre to build and would be legal. Now the industry could compete on price, not quality. The real problem has been that the government never moved the finish line. While the rest of the world has upgraded their building codes (the UK/Ireland/Wales, six times in the same time span), New Zealand’s building code has been adjusted, once, the introduced H1 (energy calculations in 2007). Square metre rate only applies to volume built, minimum code housing. There is so much more to take into account than just price.
Where is the best place to spend my money?
The best money you can spend on your new home or renovation is where you will never see it. Insulation, air tightness are two basic items that make a huge difference to any new home or renovation. Good ventilation, energy efficient windows etc. Warmer in winter and cooler in summer. Please prioritise this over the stone bench tops and ‘gold plated’ taps, you can, and probably will change those in time to come.
Why Airtightness, shouldn’t my house ‘breathe’?
A major factor in energy loss in New Zealand homes, is air tightness. The building code says ‘you should consider air tightness’, nothing more. If your home changes the internal air every hour, through the walls and windows, then you are reheating or cooling that new air every hour. Control of this movement or loss of air, means controlling the energy required to heat and cool the home. A code built house will change the air 6-7 times an hour. A ridged air barrier brings that air movement down to 3 air changes an hour. But if you use a ridged air barrier, you must, use a mechanical heat recovery ventilation system to change the air and keep the home healthy. We live in a country that has relatively high humidity and we create humidity in our homes everyday, so we must control this humidity to remain healthy.
Remember, you can have all the insulation in the world but if the wind can blow through it, then it’s a waste of time and money. Think of it, as if you are standing in an open paddock, you’ve got a lovely thick woollen jumper on, but there is a southerly wind blowing off the snow caped mountains, you’re not going to be warm until you put on a wind break.
Why do I need an Energy Recovery Ventilation System?
If you use a ridged air barrier, or a RAB and air tightness wraps, you will be controlling the air movement from inside to outside the home, through the walls and gaps in the framing. The problem being, we humans will still be living inside. We breath out carbon dioxide, we create humidity with showers, cooking, etc and this will build up in an air tight house. You need to change the air mechanically without loosing all that lovely energy you have trapped inside the house. So we use a specialised ventilation system that changes the air but recovers the heat and puts it back into the house.
People also ask ‘if I put in an energy recovery ventilation system, can I open a window. Yes, no problems, live life normally, it’s for when you need to control that heat loss in winter, and you don’t want to have the extra power bills.
What would you recommend as the ‘Basics’?
My recommendation is to have a base line for your new build. Position the home to take advantage of the sun and wind. Insulate your foundation. Use a Ridged Air Barrier on the exterior framing. Have your exterior framing 140mm, instead of 90mm framing. Fill this framing with R4.1 insulation or better, have a service cavity installed. This is a batten that goes on the inside of the stud work with an internal wrap between, and the plasterboard is then on the outside of this. Your electrical wiring and plumbing goes in this cavity instead of through your ‘air tightness layer’ which is the external framing. Have your window/door joinery moved into this air tightness layer of insulation. This will control moisture on the glass because the whole aluminium window is no longer exposed to the outside cold air, only the front face of the window. Install R5.2 or better insulation in the ceiling. It is actually quite cost effect to have two layers of R3.6, which gives you R7.2. You put one layer of insulation at a batt between the rafters and then a second layer of blanket going in the opposing direction over the top of the first layer. Have a balanced mechanical heat recovery ventilation system. All of these measure will take about 5 to 7% of your budget, but the change in comfort level will be out of this world.
How far should I go?
That is entirely up to you and your budget. It doesn’t matter if you have a $500,000 or a $5,000,000 budget, it’s never enough, so do the best you can. Having said that there are so many little things that can be done that, adds up to a huge difference.
One thing I have noticed is that people who live in energy efficient houses tend to live in them longer. Not only because of better health and wellbeing outcomes but you would never want to go back to a ‘code built house’.
Will I get my money back if I build an energy efficient house?
Let me get this off my chest; the sooner New Zealanders stop seeing houses as financial asset builders and see them a home to be lived in and enjoyed, the sooner we will have a better built environment for our communities. We are the only country in the world that has an industry built around and focused on, creating a profit from residential housing.
Having said that, as more and more energy efficient houses are built and compete with code building housing on the re-sale market. The more people will appreciate the value of an energy efficient home, when compared to an average home and they will pay more. We are already seeing that start to happen, in a small way.
What are the Benefits of Low Energy?
Energy use in the home has a major influence on the health of the occupants. If you can only afford to heat one room of your home, then your health is at risk. If your home is to have a concrete floor (and most do) I highly recommend you insulate the slab and install an in-slab hydronic heating system. This is a very energy efficient form of heating. It doesn’t rely on air movement, on burning fuel, it is constant and holistic. You can have the same temperature in every room. We can also design to ensure it takes advantage of passive heating to create thermal mass.
What are some small steps I can take?
Every little bit helps with energy conservation. Not only conserving electricity but water is a major part of consumption in most NZ homes. You are going to be buying appliances, light fittings, taps, shower heads, heating, etc, for you new home or renovation and making your selections around energy use, all adds up to a low energy home.
Why should I Recess my Windows?
The weakest part of an external wall, in any home, is the windows and doors. The building code was written around keeping water from entering the framing of the house, not around thermal efficiency. The building code says we must have the aluminium window and door joinery suspended in a cold, draughty cladding cavity. So we take the weakest thermal point of an external wall, position them away from the insulation layer (the wall) out in the cold, and then wonder why condensation forms on the joinery and glass. The simple act of setting those windows back into the insulation layer (read; insulated timber framed wall) and having a flashing system that takes any water falling on that window, out to the outside of the dwelling, improves the thermal efficiency of those windows. When you have done that, you can improve the thermal efficiency of those windows by employing thermally broken aluminium joinery, or uPVC or Timber or even Fibreglass.
Should I Collect Rain Water?
World wide water has become a commodity with a price on its head, and yet we waste huge amounts of water every day. Think about this; when it rains, water lands on the roof of our homes, we collect this water, put it into a pipe and dump it at sea. We then, drill down to an underground aquifer or tap into a local stream to water our gardens. There are many options now to collect and re-distribute rain water, and some councils are mandating it.
Why should I consider Acoustics?
Part of the holistic approach to the comfort of a home is acoustics. It is an aspect of a home that is seldom considered but it can be a game changer to comfort. As we age, our hearing changes, and this can become a distraction to everyday life. Most new homes have areas of very hard surfaces, tiles, wooden floors, concrete finishes, stone benches, in the main living areas. Which unwanted sound bounces off and can become uncomfortable when we mix music, conversation, and general noise from inside and outside the home. There are a selection of materials that can be used to dampen this noise pollution and give comfort.
Skylights, why do I need them?
We employ good design and construction methodology to keep the heat in the home, but there are times when we need to get rid of this energy/heat. Passive ventilation
is part of this good design. Creating natural, cool convection in a home is very important. Low level external windows and a couple of skylights go along way to creating this air flow. Understanding the natural wind directions of the site is the other. Ensure that you employ skylights that have internal blinds because skylights can also provide passive heating and you don’t want that when you are trying to cool a home.
How do I control over heating?
Controlling passive heating
is an important part of controlling, over heating in any home. Internal blinds/curtains help but shading the external glass is the most efficient way to control that passive heating. If the sun can’t get to it, then it can’t absorb the heat. There are many ways to achieve this. Soffit overhangs, verandahs, a Breeze Soleil, LowE glazing, vegetation can all be employed to control passive heating. The strategic placement of a deciduous tree that gives shading in summer and allows light in, during the winter, is just one way to achieve some control.
You can use these links to learn more; and if they spark more questions in your mind, you can always contact me for some answers.