Countless factors need to be considered to build a sustainable house. This is especially difficult when building large structures with multiple stories. Large teams are hired,  comprehensive studies are conducted and time-consuming simulations are run. Such measures have their place in large-scale buildings and are useful for relative comparison. Building a sustainable home need not be that difficult.

Here are three factors to look into;

1. Water

Water permeates all aspects of our daily lives. We extract large quantities from the ground. We store large quantities in tanks. Even larger quantities are used over our lifetime. Once used, water also has to be drained in some way. Since most places do not have direct supply, boreholes are a common source of water in Kenya. The borehole water supply is more stable. This will not stay that way if too much is extracted at a time. Cities like Mombasa are slowly expected to have issues of borehole supply for exactly that reason. It takes time for water to recharge the aquifers. There is only so much we can extract within a certain period. Taking too much or drilling too many boreholes close to each other affects that supply over time. This is further aggravated by the impervious hard surfaces within cities. Water needs can be supplemented by rainwater harvesting. Depending on the expected rainfall in an area, it can be used as the main source of water. The amount of water collected is affected by the annual rainfall and roof surface type & area used for your home construction. Harvesting rainwater also reduces the burden of stormwater management by lowering peak flow rates. Rainy season floods that exceed drainage system capacity lead to overflows that are detrimental to the surroundings. The effects of these floods can also be decreased by reducing the use of impervious hard surfaces. Landscaping using permeable surfaces or a combination such as grass concrete pavers helps avoid water build-up on the surface. They are also vital for the gradual recharging of the groundwater reserves. Water usage can also be optimized to reduce wastage by reuse and efficient usage. Grey water (waste water from eg. the sink) can be reused for toilet flushing and irrigation. These require minimal changes in plumbing. Using water-efficient fixtures will reduce wastage of water. A general strategy of reducing wastage through adoption of water-saving habits makes a huge difference in the long-run.

2. Energy

The fact that you are consuming energy (electric power) as you read this is enough to prove how important it has become in our lives. It is a hot day as I type this and the fan is on. The space is fairly shielded from the sun as it is surrounded by trees so I have to switch the lights on in some spaces even during the day. In warm places, enhanced ventilation can reduce the use of fans and AC within the house. Mechanical ventilation is not as healthy as natural ventilation. Increasing access to natural lighting within the house can reduce usage of light during the day. Artificial lighting during the day is just not the same as sunlight. Lighting fixtures with lower rating are a great option for reducing the long-term power consumption. It is also great to use renewable energy options such as solar and wind power. Though very common and now in vogue, I do not understand the full life cycle of the different options and products to confidently call them sustainable. Nevertheless, switching to renewable sources such as solar is increasingly becoming feasible. Most businesses are switching to solar. The one thing that indicates, more than the supposed concern for the environment, is that it makes economic sense. Other sources such as wind and biogas are options to consider. While using renewable power sources is a plus, it is not as effective as reducing power consumption altogether. I am not advocating for complete shunning of the possibilities that the electricity-powered devices afford us. Consumption of energy can be reduced by using energy-efficient appliances. There are places where we are using the tech in place of better & natural options.

3. Materials

Building materials form the essence of any construction project. The bulk of the house and cost depends on the building materials used. Ideally we want to reduce usage and wastage of these materials. Whenever we do use them, we want to do it responsibly. The materials we use affect us and our health. The best way to reduce material usage is to limit the size of the built structure. This can be done by minimizing excessively sized spaces within the house. Multi-purpose spaces can also be planned so that you have one common space instead of separate spaces that are seldom used. Reducing wastage requires creative thinking and careful planning. Broken tile pieces can be used in outdoor spaces. Careful dimensioning of some details can help avoid wasted remnants. Some products come in standard sizes. Adjusting a few details to fit the sizes exactly can reduce waste. Natural materials that have been carefully sourced are an ideal option. Getting what is locally available is one of the best things you can do. This reduces transport distance to the site which saves on potential pollution. Local materials would not need labour sourcing from afar to get the required know-how. The final form of the materials should have been subjected to minimal processing to reduce the impact it would have had. On the site, materials that require less machinery to work with will reduce energy consumption. Using recycled materials such as plastic and glass bottles is common. I am biased against both. They can, however, be a good option in places where you cannot avoid them. If you are going to use plastic, it might as well be recycled. Considering the reusability of materials from the start can be even better. The use of modern materials commonly used in different parts of finishing such as paint have a negative effect on our health. Careful choice of these is necessary. Deliberate use of design strategies that avoid them altogether would be better in the long run.

There are other factors such as lighting and landscaping that can also be looked at. Setting up of the site and building techniques are also important issues to consider. Water, energy and materials are a great starting point. They have a huge impact and some of the modifications suggested do not take much to incorporate. 

The question of sustainability tends to be posed incorrectly in my opinion. It should not be whether you want to build a sustainable house. The better question is how sustainable you want the house to be. Not all standard practices are unsustainable just as not all aspects of sustainable homes are sustainable. While quantifying sustainability can be difficult without using a consultant or some common simulations, you do not necessarily need that level of accuracy. 

Most of the considerations suggested above are simple to understand. Applying them can be just a little bit harder. The difficulty should reduce over time as the necessity of sustainable building becomes apparent and the approach becomes standard. Three principles to start with are outlined here.