The best solution?
I'm really pleased to have another guest post from Mark Brierley for you today (you can see his first one here). Mark is a certified Passivhaus consultant and blogger, and he is generously sharing his knowledge and experience with us today. You can read more of his writing at his excellent blog, or stay tuned for another guest post from Mark next week.
"The easiest and most effective time to insulate a house is when it is being built, and if you are involved in building a house, it makes sense to invest in lower energy use. Even if you can afford to buy a house with cash, the tax breaks you get from having a mortgage in Japan mean that you are better off borrowing money for your house, and following other suggestions in this blog to get higher returns on your own cash.
Financially, there is always a trade-off between the up-front capital cost of insulation, and the running costs for heating or cooling. If you are borrowing money to build your house, then your capital payments are not up-front investments, they are monthly payments. Your energy bills are also monthly payments, but the energy bills will continue after you have paid back the loan. Nobody has a crystal ball, but there is at least a fifty percent chance that energy will become more expensive rather than less expensive. On the other hand, Japanese banks offer cheap fixed-rate loans, so you know exactly how much you will be paying. Investing in insulation means you pay less overall, and you are also insulated from any spikes in energy costs.
Not all insulation is equal
Heat is lazy, and will always find the easiest way to get from hotter places to colder places. The same principles apply to heat whether it is leaving your warm house on a cold winter night, or coming into your cool house on a hot summer day.
Heat has basically two ways of escaping: conducting through the walls, or leaking through gaps as hot air. This means that along with the insulation, your walls, floors, ceilings, doors and windows need to be airtight. If you have an airtight house, you need ventilation. If you use natural ventilation, such as air vents or opening windows you will lose a lot of air and the heat with it when it is windy, and you will not get enough fresh air when it is still.
Mechanical ventilation means that you get the right amount of air for a healthy and comfortable house. Mechanical ventilation can also use heat exchangers which warm up the fresh air coming into your house with the heat from stale air leaving. The electricity used by the fan may seem like a waste of energy, but it uses much, much less than the heat you will save doing this. Mechanical ventilation will only work effectively if your house is airtight. You can imagine how ineffective it would be to suck air through a straw with lots of holes in the sides.
This combination of insulation, air tightness and mechanical ventilation with heat exchange is the basis of the Passive House standard, which I think is a gold standard in low-energy building. Passive House, or Passivhaus in German, came mostly from a German and Scandinavian reaction to the oil shocks of the 1970s. It is built on forty years of research and measurement, and the experience of several failed attempts to build low-energy houses.
Even if you are not trying to reach the Passive House standard, you can learn a lot from the research into using less energy, and avoid many problems that can come from attempts at low-energy building. You can read more about my experience building and living in a Passive House in Japan here. You will need to research this because unfortunately you can't just walk into a builder in Japan and pick up a Passive House off the shelf.
As well as saving money, better insulated houses are more comfortable, healthier, and can last longer since the insulation will also protect the structure. In many countries energy efficient buildings have higher resale values, but building resale values in Japan are low, energy efficient buildings are scarce, and it is difficult to find evidence of this being true in Japan.
Well-insulated houses are cheaper to heat, but partially insulated houses will not necessarily save any money. As mentioned above, all insulation is not equal, and needs to be carefully designed and properly installed to reduce your heating bills.
Actual energy use is often twice the predictions from regular building codes, but the decades of research and measurement of Passive House buildings in a range of European climates mean that energy use is very close to the predictions, and these buildings reliably use up to 90% less energy than conventional houses.
If installed correctly insulation will always make your house more comfortable, but unless you have a well-insulated house you may end up paying the same energy bills as before to make your house comfortable for more of the time. Moderate insulation will give you a choice between comfort or cheaper heating bills. The performance of Passive House means that you can have both comfort and lower energy bills."
Thanks again Mark. Lots to think about there. I am planning to build a small Passivhaus in a few years time -hopefully the concept will have become more popular by then!
Any questions for Mark? Feel free to post them in the comments, and stay tuned for next week's post.