You don’t need a super-fantastic-amazing funny-looking low energy house to cut down your home energy use if you know what you’re looking for. Not every house in suburbia is a low energy house. You have probably noticed it yourself. Some homes are just naturally bright and sunny. They’re always nice to be in and mysteriously toasty warm in winter. During the summer, all the owner has to do is open the back door and a cool breeze magically flows through the house. Other homes are the exact opposite. In winter, the sun never seems to come into the windows. The cold breeze rattles the floorboards underfoot. And that state-of-the-art gas heater only seems to warm the few inches of air around it. In summer the heat is oppressive and no matter what you try, even with the air conditioning turned up all the way, it is always more comfortable under the tree outside.
By David Shankbone CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0/)], via Wikimedia Commons
These differences, especially amongst generic suburban house stock, are usually accidental. One building that perfoms beautifully will sit next to one that is completely useless. The trick is telling one from the other. Finding the low energy houses. They will sell for (or rent out at) the same price. But one will require almost constant electric heating and cooling, lightbulbs switched on even during the day, the most elaborate coping mechanisms (like doing the dishes by hand in winter time – to keep your hands warm) in order to cut electricity (and therefore carbon) consumption. So what do you look for in order to invest wisely in your comfort, reduce your bills and avoid one of “those” houses?
The heating and cooling of spaces accounts for the majority of the energy (and therefore carbon) consumed in a house so it is really important to get orientation right. What you are looking for is a house that gets a lot of sunlight coming into it during winter but is nice and shaded in summer. This is actually pretty easy because the sun is in a different position in summer than what it is in winter. In summer, the sun hangs almost directly overhead (rises in the East and sets in the West – something we all know). So living rooms with a lot of windows to the west will get a lot of hot sun coming in all throughout the year – especially in summer. So the first step, especially if you live in a hot climate like I do in Australia is avoid any houses that have main rooms with big windows to the West unless they have a fairly large overhang (like a verandah) that will shade almost all of the sun out. Another solution for west-facing facades is to grow a deciduous climber like Virginia Creeper over the wall. This will shade the house during summer, but when the leaves drop off in winter, the sun will get through and warm up the wall.
During winter, the sun still rises in the East and sets in the West, but as it flies up and overhead, it does it at a more Northern angle in Australia (a more Southern Angle if you live in the Northern Hemisphere). So living rooms that have big windows with no (or a very small) overhang or eaves to the North (South!) is the most important thing. The small overhang will stop the sun getting in during summer but your room will be wonderful and bright and warm during winter. When I was a kid, my dad would always talk about whether a house was “facing the right way” or not. This is what he meant. When looking at a house, is the main living area facing towards the winter sun? This will save you more money on heating than anything else. It is an absolute must for people who live in fear of their heating bills.
I have seen first hand the amazing difference that insulation can make to the comfort of a house. Never move into a house that has no insulation in the roof. In summer the roof space inside your h0use can warm to 40 or sometimes even 50 degrees celcius. This heat will radiate down onto you. During winter, the warm air inside your house will rise (warm air rises) and seep up into the roof space leaving you very sad and cold. The roof is the most important part of the house to have insulated. The walls are the next important, followed by the floor. But if you live in a cold climate, make sure there are no cracks in the floor and the wind can’t whistle in underfoot. That is no fun.
The heating of water (for showering, the hot tap in the kitchen and in some cases heating the house) usually accounts for just over a quarter of home energy consumption. Have a look at where the hot water heater is placed. Is it in a shadow under the house? Is it against the hot western wall? The latter will be cheaper because the sun will heat a lot of the water for you. The former will rely entirely on your lovely big carbon footprint.
All windows, even the best-glazed of all, allow more heat transfer than even the most basic single leaf brick wall. If you live in a hot climate, avoid houses where a lot of sun is going to shine onto windows (thankfully, houses like the Queenslander generally have shaded verandahs right the way around which cancels out this problem). In colder climates, having a lot of high windows can be an issue. Even if they are double glazed, they are less efficient than the walls around them. Skylights are a big culprit as the heat from your room will rise to the ceiling and then drift through the glass and outside.
Of course, the opposite is true as well. In a cool climate, good north facing windows will let in a lot heat during the day. Just make sure to have good curtains with pelmets to close at night.
A note on curtains – when you shut your curtains during winter, they operate as air conditioners. The small space between the glass of the window and the curtain will get cold because the air outside will cool it down. Cold air sinks. When this happens, the cold air will leak out below the curtains causing a vacuum which will suck warm air in from the top of the curtain. The cycle will continue when this warm air gets cold and leaks out the bottom of the curtain. The best way to stop this is to put a pelmet (or a rolled up blanket) above the top of the curtain to stop the air cycling. It makes a significant difference to the warmth of a room in winter.
In a hot humid climate it is important to be able to open up a house and receive a decent amount of ventilation. The fresh air will prevent the house from becoming musty and damp (if you notice any damp corners when inspecting a house… walk away). Often, you can get enough fresh air by the infiltration of fresh air through the construction (which you may not even notice) but this won’t help cool you down. To maximise ventilation, look for houses that are only one room thick and have windows on both sides of each of the rooms. Another great layout is if one corner of the house has large windows, and the corner diagonally opposite has a small window. The breeze will be most noticeable in the small-windowed-room as the air rushes through the tiny exit. In a hot, dry climate, ventilation is less desirable as the hot, dry breeze will not cool you down at all. It may even make the house significantly less comfortable.
Due to their thermal mass, rammed earth walls take nearly twelve hours to transfer heat through from outside:
Image: Architecture Republic. See the whole project here.
Thermal mass is an interesting phenomenon. Think of heavy materials (concrete, asphalt, stone, rammed earth) and how they tend to absorb heat more than lightweight ones. After a long hot day, the surface of the road will still be warm where everything else has cooled down. This is because the road is thermally massive. Thermal mass can be used to your advantage. Little details like heavy stone tiles on the floor below where the winter sun comes in actually do make a big difference to the heat of the room in the evening. In summer, these tiles will remain shaded and cool underfoot. Some of these modifications (like adding some heavy stone tiles under windows) are easy to do yourself and can be taken away once you move on. Other modifications (like installing thermally massive wall heat-banks) are more permanent solutions that will see you into the future.
Time Lag is where the warmth of the day takes a while to get inside the house. This is pretty common with stone, earth and haybale houses (anything that is thermally massive). With insulation, heat will touch one side but will never get through to the other side. With a stone wall, the heat will touch one side, make its way through the thick wall, and (sometimes 12 hours later) eventually make its way inside. This is great if you get hot days and freezing cold nights as during the day, your walls will be cool from the night before. When evening hits, the walls will be warm from the sun being on them all day and will keep you warm at night. BUT! if you live in a climate where the summers are hot during the day and night… and the winters are cold all day and all night (ie: Sydney), then this effect won’t be as important as good insulation.
Dark colours tend to absorb heat, whereas light colours more effectively reflect the sun’s heat. There is almost n0 advantage to using dark colours on external walls and roofs to assist with heat gain in winter (its better to heat the house from within or by solar gain) but dark coloured floors inside the house (especially where the winter sun will shine) can be advantageous. In summer, dark houses will collect a lot more heat than lighter coloured houses. Recently, in Australia, it has become fashionable to have black roof tiles. One of the more ridiculous ideas in the history of Architecture in this country. Avoid houses like this if you wish to survive the summer.
By keeping all of these principles in mind (and paying attention to the way buildings around you perform) you will quickly be able to tell which houses are going to keep your bills in check and which aren’t. With a bit of creative problem solving, you might even be able to change a few things around in order to make your home more comfortable. Please try to keep in mind that things like orientation, insulation and the placement of thermal mass are much more important than whether your house has a walk-in-wardrobe and what colour the shower screen is.