Wednesday, 7 November 2018

Squaring the Circle for Traditional Buildings

It often seems that there is a battle going on between traditional building techniques and high-insulation high-airtightness approaches such as Passive House. Advocates and practitioners of traditional buildings have a strong case that years of experience will show how and when buildings fail, and how they can be built to last. They claim natural materials can absorb and release moisture and are free from dangerous chemicals, so they are better for the building and more healthy for the inhabitants.

But traditional buildings do not use a lot of insulation and are not airtight, so here are two questions: 
How do you keep a traditional Japanese building warm in the winter? 
How does ventilation work in traditional Japanese buildings to ensure good air quality?
I'll get to the answers soon.

High airtightness is sometimes achieved with synthetic membranes, but concrete, plaster on stone or brick, and oriented strand board (OSB) can also play a part in a building's airtight layer. Insulation materials are often polymer-based, especially where a high performance is needed. To get the same insulation as ten centimetres of top-grade foam, you need over 30 centimetres of thatch, over 80 centimetres of wood, a similar thickness of clay mixed with straw, or over two metres of rammed earth. Cellulose fibre insulation is better than all those traditional alternatives, but you would still need over twice the thickness to match foam.

It is interesting to note that a mixture of clay and straw has a similar insulation level to wood, which means that a structure of wooden posts and pillars filled with traditional walls may have an even layer of insulation, avoiding cold spots. But a typical passive house wall has something like ten times higher insulation than a traditionally-built house, so for those walls to perform in the same way, they would need to be ten times thicker.

So how do you keep a traditional Japanese building warm in the winter?
Short answer: You don't. 

When it's cold outside, it gets cold inside. The walls are porous so moisture does not tend to build up. If you want the house to be warm you have to start burning stuff. Today that stuff is usually fossil fuel, either directly, or indirectly with electricity generated from fossil fuels. So you certainly can build with traditional, natural materials, but the inhabitants are only going to be comfortable with a steady flow of un-traditional, unnatural fossil fuels. 

Traditional Japanese heating is with wood burnt in an irori open fire or charcoal smouldering under a kotatsu table heater. Irori are open fireplaces in the middle of the room. Traditional Japanese buildings don't have chimneys, so the smoke finds its way up though the house, killing any bugs on the way, and then out through the ample gaps in the structure.

Traditonal kotatsu burn charcoal in a small irori pit, with a table over the top covered in quilts and blankets. The kotatsu just provides a warm space to sit in rather than warming the whole building, which in some ways is a very efficient use of fuel. This 1820 woodblock by Eisen Keisai also hints at other ways couples kept warm on long winter nights. 

Today people do not want open fires because of the risk of the house burning down, and the increased soot and extra cleaning. Charcoal-burning kotatsu are also a carbon monoxide risk so modern kotatsu use electric heating elements. They are still occasionally fatal because of the heat shock when elderly people get in or out of them. Many people in Japan love their kotatsu, but if they start living in an insulated house, they do not miss them!

Most Japanese homes do not have any central heating system, often relying on kerosene fan heaters, electric carpets, or air conditioners in heating mode. Some houses have underfloor heating, but there are frequent stories of people who use it for one year, see the electricity bill, then never switch it on again. None of these heating techniques is traditional or natural. 

Wood burning stoves may be a more natural method, and cast iron stoves from New England or the west coast of Ireland do look very nice in Japanese houses. The rituals of preparing wood and the cleaning and maintenance may not suit everyone's lifestyle, the smoke may not please the neighbours, and unless the house is in the middle of a forest the source of wood may not be sustainable. An increase in wood-burning stoves has been blamed for poor air quality in London, and since London is not a major producer of wood, you also have to wonder about the carbon footprint of transporting the fuel. 

Wood pellets are much more efficient than burning wood directly, which not only means less wood, but also less ash to clear from the stove and less pollution going through the chimney. The first wood pellets were made from sawdust waste from timber mills. However, as demand increases, and efficiency leads to less waste, trees need to be specially cut and grown for wood pellets. Economically speaking, pellets may have started off being made from a waste product with zero cost, but as and demand increases, the price may go up. The impact is not zero and while burning wood pellets may be better than burning fossil fuels, they do not provide a solution to the world's energy problems, and whatever you are burning, it's still better to burn less. Ideally some of the trees in our dwindling forests will be left as habitat, and end up falling to the ground and emerging in a few millennia as a carbon source for future inhabitants of the planet. But I may be digressing from the topic of traditional buildings. On the other hand, preservation of the environment may be exactly what advocates of traditional building want. 

If I may return to more urgent matters of survival, when a building is airtight, it must be ventilated. The solution used in most passive houses is a mechanical ventilation system with heat recovery. Advocates of traditional building techniques often have a visceral reaction to the idea of mechanical ventilation as it is clearly not a traditional way to ventilate buildings. It uses electricity, so how could that ever be natural?

It is not natural. But what exactly does "natural" mean? When people call for natural materials, what are they asking for? Asbestos occurs naturally in the ground, but I'm guessing you wouldn't want that in your natural building! Polyethylene and polypropylene are completely synthetic and harmless to taste and touch.

If you really want nature, you should go and live outside. Buildings are not natural. Rather than asking a binary question whether specific materials or techniques are natural or not, we need to look at health, comfort and energy use, over the lifetime of the building and make the least bad decisions to get the best health and most comfort for the least energy use and lowest environmental impact.

So how do you ventilate a traditional building? 
I'm temped to say that you don't, but of course traditional buildings are ventilated—just not in a very systematic way. If there is a fire in the building then it is also working as a ventilation system by sending hot air up and out of the building while drawing air in through those thoughtfully provided gaps and porous surfaces. When there is no fire, air must find its way in and out through open windows and doors. The amount of natural ventilation then depends greatly on the outside temperature, wind speed and direction. So if a house is designed to always have fresh air, it will usually have too much ventilation. This will lead to uncomfortable drafts and a steady loss of heat. If it is designed to minimise drafts and heat loss, then there won't be enough ventilation for good air quality and control of moisture. 

The traditional builders will usually choose too much ventilation because that is the only way to guarantee there will be no moisture build up. So the house should not be airtight. If the builders do make the house airtight, they need to put in mechanical ventilation. They could ensure ventilation by providing a fire for you to keep stoked, but if they do that, they need to make sure there is no risk of carbon monoxide poisoning, which again will probably mean avoiding airtightness.

Mechanical ventilation does use electricity, but it provides fresh air, takes excess humidity out of the house, and keeps you warm very cheaply by recovering the heat from the expelled air. Heat recovery ventilation will only work if a building is airtight, making sure that air is coming in and out through the heat exchanger. Also, the insulation will only work effectively and without risk of condensation within the walls if the building is airtight. And if the building is airtight, active ventilation is needed because natural ventilation is unreliable.

Without active ventilation and airtightness, extra insulation is a risk as air leaking out of the house in winter drops in temperature and hits the dew point, producing condensation.

So the traditional builders are going to hand you a choice: 
Pay a lot for heating, or be cold. 

On the other hand, a traditional structure can be wrapped in an airtight insulating layer, and include a ventilation system. This will protect the structure and make it last longer, and will make it nice for the inhabitants, who probably do not want to live a traditional life that is not as comfortable and not as long.

In the fight for survival of traditional building, insulation, airtightness and active ventilation are not the enemy. They may be the saviour! 

Emissions from Wood: