Innovative Houses: Concepts for Sustainable Living (2014)

Is it possible for each of us to produce as much energy as we use?  Could well designed homes enable each  us to do so for the same price as a traditional home?  Well, that has been the objective underpinning "net-zero" design principles since the idea's first incarnation as the “Passivhaus” project in Germany in the 1990s.  Modern construction, energy, telecommunications and design technologies are now beginning to work in tandem to deliver self-sustainable housing.  In Innovative Houses: Concepts for Sustainable Living, Avi Friedman (an architect) uncovers some of the newest principles and practices that are making "net-zero" a potentially ubiquitous practice.

Sounds good, but what possible reason could you have for wanting to build such a thing (besides achieving new levels of pretension at your next Shoreditch supper club)?

Well, net-zero houses divert the generation of power away from conventional, polluting power plants and into local, more sustainable and cleaner methods.  They drive down consumption of both energy and resources and inspire an ethos of collective and individual responsibility in a society that is still geared towards unsustainable mass consumption.  Plus, in my opinion, they’re really cool.  They often incorporate the most cutting-edge technologies and contemporary design principles in order to create a home or office that looks and feels genuinely modern and creative, whilst continuing to serve that larger societal and, often economic, need.

With that in mind, I’ll share and comment on the major net-zero design considerations raised by Friedman.  Hopefully this blog entry will be one of my more practical pieces and should be informative for anyone interested in designing a net-zero home or office, or anyone just trying to reduce the energy consumption or environmental footprint of their home.

In order, I’ll be looking at:

• architecture and orientation,
• energy and resource efficiency measures,
• implementing on-site renewable energy, and
• other sustainability considerations and trends (e.g green roofs and home farming).

In addition, I’ll be including photos of some of my favourite net-zero homes featured in the book.

Architecture/Orientation

One of the central tenets of a net-zero building is that you don’t actually have to put in much energy, or prevent much energy from escaping, if you design it in order harness natural sunlight and airflow.

Aspects such as the building’s dimensions and site orientation are critical to taking advantage of passive solar gain, natural daylight and indoor airflow, which can all help to regulate internal temperature for free and without energy consumption.  There are also much larger decisions that designers must consider before even purchasing a site, such as: the local wind patterns, sun orientation, topography, the ground depth of winter frost and shadows cast by other buildings and trees.

Principally, a building should be orientated so that it has the elongated side facing south (or north in Southern hemisphere).  Facing true south, rather than magnetic south, is highly recommended, but the orientation can vary by up to 20 degrees with minimal effect on solar input.  This orientation allows that building’s side to gain energy between 9 a.m. and 3 p.m. during the cold season.  In summertime, when the sun is high in the sky, it still moves along a southward arc in the Northern hemisphere.  According to the California Energy Commission (2011), by designing a house to take full advantage of the sun’s heat, energy consumption can be reduced by 30 to 40 per cent.  In colder climates, however, such an organisation can reduce the heat load by up to 60 per cent.

The south-facing façade should contain large windows for ease of solar exposure.  In contrast, the opposite façade should have fewer openings and more insulation in order to minimise heat loss.  To reduce the heat loss from the northern façade, it is recommended that only 5 to 10 per cent of its surface should be fenestrated. 

Primary living spaces, such as living rooms, kitchens and bedrooms, which require the most heat and light, should be placed along the wall with the highest sun exposure (and should be top-lit by an opening, which doubles as a wind catcher and light funnel).  Secondary or less used spaced, such as utility rooms and stairs, should be located on the north side.

Designing a house to have windows near the ground and others near the top of a room improves natural ventilation and high ceilings also encourage airflow, which can then be seasonally controlled.

Designers can then use two types of thermal reservoirs to reduce heating and cooling needs: green roofs and/or basement crawlspaces.  Both methods rely on absorbing heat during the day, thereby keeping the house cooler, and releasing that heat at night to keep it warmer. 

Since mechanical heating and cooling systems usually account for around 55 per cent of overall household energy consumption, net-zero housing is smart in first utilising these natural (and free) methods for reducing demand.

Energy and resource efficiency

Nonetheless, natural sources are unlikely to be able to satisfy heating and cooling needs all year round, in all climates.  Consequently, we always need to think about how we can increase the efficiency of the energy and resources we do use.

Lumber, iron ore and fossil fuels are among those materials whose stock is rapidly disappearing, but which remain crucial to the construction industry.  The need to develop housing prototypes that consume fewer resources and recycle others during their fabrication and occupancy is an urgent priority.  Homes need to intelligently regulate the energy they use, take advantage of the sun for energy generation, use construction products made from recycled material and be water efficient.

To that end, adjusting your thermostat is hopefully going to become one of those archaic behaviours of a bygone era.  We now have sun, wind and heat capacity calculating software that communicates with smart thermostats and energy usage readers in order maximise the efficiency of your heating and cooling systems (with minimal input from the user).  You may have noticed that these devices have quite recently reached a tipping point with companies like Google and British Gas developing and aggressively marketing home smart meters that can be controlled from anywhere, through your phone (“Nest” and “Hive” being their respective companies/products).

In terms of actually heating and cooling your home, it is important to maintain airflow throughout the structure using suitable heating ventilation and air conditioning (HVAC) methods or heat-recovery ventilation (HRV).  These appliances recover the heat as it flows outside and transfer it into the new, fresh air that is entering the building.  This is a very efficient method to reduce wasted energy through heat loss.

For heating considerations, there are multiple air and water methods that you can choose from, such as baseboard heaters, fossil fuel central heating systems, active thermal solar heating and geothermal heating.  They can be combined with others such as HRV and designed for passive solar gain. 

For ventilation, you can choose from central duct, passive circulation and simple ductless convection systems.  These can be enhanced through the usage of the thermal chimney effect, the ridge-and-soffitt vent system, grille selection, underfloor displacement ventilation and filter selection.  For air conditioning, it is advisable to use passive cooling options – such as natural and artificial shading, thermochemical glass, the thermal chimney effect and geothermal cooling, among others – prior to resorting to costly energy consuming technologies.  Once passive air-conditioning systems are introduced, there are numerous methods to choose from for active air conditioning.  They range from individual space coolers, such as window units, to central AC systems and are selected on the basis of efficiency and cost.

Further green technologies are maturing and gaining greater market share, such as: biomass boilers, rainwater collection systems, a multitude of water efficient appliances and phase-changing materials (primarily embedded within walls/insulation) that absorb heat in the day and release it at night.

Water is an often overlooked resource.  However, research has shown that homeowners can make incredible reductions in use by focusing on increasing appliance efficiency and decreasing flow rates.

Conventional toilets currently account for 27 per cent of total water usage, so modernising your toilet is actually an investment that usually has a very short payback period.  Waste-water recovery systems perform the same functions as the HRV mentioned above but for water, by transferring heat from used water into potable water before it flows into the sewage system.

Furthermore, there is a clear effort to utilise “grey” (recycled/unfiltered) water for uses where strict cleanliness is not necessary.  Consequently, grey water harvesting and recycling systems take water from the shower, sinks and laundry and use it to either flush toilets or irrigate outdoor vegetation.  Cisterns also allow homeowners to collect and distribute up to 1.42 ltr (0.375 gal) of rainwater per 0.09m² (1 sq ft) of the catchment’s area, per 2.5 cm (1 in) of rain fallen.  This collected water, rather than water supplied via the mains, can then be used for similar purposes.

On-site renewable energy

If you’ve followed the plan so far, you’ll have a home or office that has a greatly reduced need for energy.  However, what energy you do require, you’ll still be drawing from the grid, so we’re still short of being net-zero.  Consequently, on-site generation of energy is necessary.

First, it is important to decide whether the dwelling will be off-grid – using batteries to store energy for low production times – or grid-tied – in which case the dwelling can draw from and give back to the local power grid.  Unless you’re some kind of eccentric billionaire who can afford to live in the remote wilderness, you’ll probably want to be grid-tied.

Solar and wind are the obvious scalable renewables most designers go to.  An area of 144m² (1,551 sq ft) of photovoltaic (PV) panels has the potential to provide all of the energy needed by the average four person household.  The efficiency and cost of solar PV panels continues to drop (see “Swanson’s Law”, which has accurately forecast since 1976 that the price of solar PV panels will drop by 20% for every doubling of the units shipped worldwide – meaning at current rates, the price halves every 10 years).  Nonetheless, it is unrealistic to expect everyone to have the space, capital and climate to power their home this way.

Consequently, it is best to combine electricity production methods (solar PV, wind turbines or whatever suits your location and budget) with other heat-production methods such as geothermal pumps and solar hot water vacuum tubes.  While such heat-production systems do not actually produce electricity, they are valuable in reducing the amount required to heat the dwelling, making electrical production more effective.

The takeaway message is that there is no one-size-fits-all solution to on-site renewable generation.  It needs to be tailored to meet specific energy requirements for specific budgets in specific climates.  The good news is that there’s a plethora of options out there and their prices are all dropping over the long-term (even if the short-term drop in oil prices causes them to look relatively less attractive). 

Other sustainability considerations and trends

Pre-pack houses/ use of space

Populations around the world are more densely packed than ever.  Added to the fact that bespoke construction and relocation costs are more expensive than ever, and it is a logical progression that net-zero homes can now be bought flat-pack for easy construction and deconstruction/relocation.  Consequently, we’ve recently seen that in Japan, more than 120,000 houses per year – one third of all newly built homes – are made in factories using online customisation.

Furthermore, design firms, like the Netherland’s DAAD Architecten, are attempting to tackle the issue of lack of space by exploring untapped urban areas such as rooftops.  Their project, Lighthouses, is an attempt to solve living congestion in urban areas by designing houses that can easily be placed on top existing buildings (obviously it would be up to you to find the location and negotiate a price and a right of way up to the rooftop).

They look a bit peculiar, but the exploitation of these previously unused spaces could rejuvenate a housing markets in thousands of cities across the world where the shortage of space makes housing prohibitively expensive for so many.  Furthermore, if we make sure that it’s a net-zero home being placed there, we’re addressing two problem at once.

Similar in principle to that idea is the German architect Werner Aisslinger’s project, Loftcube, which offers a dwelling that suits people with a ‘nomadic’ lifestyle and allows for temporary stays in dense urban areas.  When you move, it moves.  While economically it makes sense to occupy unused real estate in urban locations, the Loftcube is, more romantically, a transportable penthouse that can be placed on rooftops, or other terrain such as mountaintops, islands and in forests.  This approach decreases waste and cost over the long run.

Green roofs

Green roofs not only look cool, but they are also (as mentioned before) a great way to absorb heat in the day time and release heat at night.  Furthermore, they turn a previously unused space into a recreational area and/or area for growing your own food.

It is possible to build green roofs on either flat or pitched roofs.  While flat roofs are the most common type, the pitch roof design is also a viable method that has been used for centuries.  The common flat roof can incorporate rooftop terraces and gardens, but this version is typically more expensive due to the complex systems and membranes required to waterproof and drain water.  The other version is simpler and easier to build as the natural slope easily drains off excess rainwater to prevent leakage.

Designing with nature

When designing and building with nature, the key consideration is the preservation of flora and fauna.  Constructing with minimal disruption to forests, for example, leads to advantages such as enhanced air quality, protection from the elements and storm water retention.  Furthermore, having large trees around the house reduced overall energy consumption by up to 25 per cent due to shading and protection from the wind.

Xeriscaped outdoor spaces

The core objective of xeriscaping is water conservation through the creation of water efficient landscapes. Chiefly, this involves planting native species with deeper roots that can survive primarily on rainwater and grouping plants by reference to water demand.   

Edible landscaping

The recommended size of an edible portion for a one-family garden varies from 55.7 to 111 m² (600 to 1,200 sq ft) depending on how active the homeowners plan to be.  If this kind of space is unavailable (which is quite likely), then there are two commonly used types of vertical farming.  The first is a simple method in which vine-like plants grow upwards using string, walls or fences.  The second consists of a layered garden in which crops are planted in two or three levels.  Using this method, where the plants that need more water are placed on the lowest layer where water permeates slowly, even modest size gardens can be used to harvest a reasonably large amount food.