This post is designed to guide design teams during early design stages prior to any form of drawing mark-up. It describes a pathway of continuous building improvement through easy low hanging fruit strategies to incorporation of renewable technologies and advanced design principles. As sustainability becomes engrained in the construction industry it is important that stakeholders maintain an understanding of what the market expects both presently and going forwards into a low carbon future.

Achieving Targets – The Basics

Generally a multi-residential apartment building built to BCA standards (electric hot water, 6 star Nathers and standard air conditioner) will have approximately the same impacts as the benchmark average dwelling (4.2 tonnes/person/year). They tend to be smaller (less space to heat and cool), have longer design lives and high occupancy (reducing the impacts on a per person per year basis). The chart below represents the life cycle Impacts of a typical multi-residential apartment building.

Typically there are a number of “low hanging fruit” design improvements that are low cost and low risk to implement. The measures focus on operational energy which generally makes up 70%-80% of the total life cycle impacts. The measures are detailed below for a standard apartment building with a mix of one and 2 bed apartments, please note these are indicative figures and will vary depending on final design, density, services and materials used.

With implementation of the above measures the building will achieve approximately a 37% to 45% improvement sitting at a Silver medal rating. To achieve greater improvements renewable technologies are needed.

The majority of medium rise flat roofs can easily accommodate the above with room left over for other elements such as flues and skylights. The low hanging fruit combined with some renewable generation will typically achieve around a 45-55% improvement.

 Achieving Targets – Best Practise

For higher ratings to be achieved, there will need to be upwards of 1 kW and per apartment and over 10m2 of roof space available alongside the measures detailed above. This can require careful consideration of roof designs from the outside and in some instances, consideration of options off-site such as community owned solar PV farms may be required.

Roof Orientation for PV:

Once a residential building gets above 4 storeys, or a commercial building gets above 3 storeys, it will likely end up in a position where the solar technologies that are required are constrained by the roof space that is available. In this situation the design team should take roof design into consideration from an early stage and optimise it for solar panel installations. The following guidelines should be considered:

• By installing panels “flat” on a roof, many moor panels can fit because they do not need separating for shading.
• Shading from surrounding objects and buildings is an important consideration however it is rarely a problem in multi-residential buildings taller than their surroundings. PV can be very worthwhile even if partially shaded and can may still deliver significant carbon savings compared to other measures.
• For designing roofs in this situation, the following considerations should be made.  Note that the below loss figure for varying orientation and pitch are applicable to Perth (latitude of 32 degrees):
• The orientation of the roof can significantly aid the amount of PV or Solar Hot Water that can be installed in the diagram above

– North facing panels at 32 degree pitch gives optimum energy gain over the whole year (100%)

– Dropping pitch to 5 degrees only results in a loss of approximately 9% (91% of optimal generation)

• If panels are to be pitched at lower than 10 degrees, consideration should be given to at least annual cleaning until it is proven that soiling is not effecting generation.
• If possible, avoid hips in roofs as these significantly reduce the amount of PV that can be installed.  It is far better to pitch the roof in two directions only.  Even pitching north and south in two directions is likely to result in a better overall result than in four directions.  The south facing panels may generate less power per panel than the east or west, but more panels will be able to be installed because hips won’t have to be avoided and this will more than make up for the slight loss of efficiency in south facing panels.
• Very wide gutters can significantly affect the available roof space for solar collectors.  Consider overhanging the roof structure over a required large gutter.
• Protruding services that break up the roof space should be designed if possible on the south side of the building.  This reduces the losses due to shade for solar collectors across the whole roof.
• Roofs with multiple heights are complex due to overshadowing.  If possible avoid this.

For solar hot water systems the same rules apply however slighting more consideration may be required to match demand with pitch, so a higher pitch to meet the higher winter water heating demand.  This is not such an issue with PV as it can be fed into the grid when generation is higher than demand.

Advanced Design

Some of the recommendations listed below represent paradigm shifts not only in actual construction but also in the marketing and sales strategies that may be required to ensure a developments viability. There may be times when it makes more sense to invest the money that would go into some of these expensive onsite solutions to other local projects that can deliver more value and higher CO₂e savings. Examples of this may include Investments in street light upgrades, existing housing retrofits, solar panels on local schools and buildings, behaviour programs, community farms, bicycle infrastructure etc.

Functionality

The more people a building can house the less impact per person that building will have. Furthermore for every person that is housed in a sustainable building that takes one more person out of the average, unsustainable building – moving society towards a low carbon economy faster.

Typical multi-residential buildings have approximately 50% of the total floor area dedicated to actual living space, the rest tends to get tied up in common areas, car parks, plant rooms etc. By minimising the common areas you reduce impacts on two fronts: living area available for the same volume of materials, and reducing the operational energy required to light and ventilate the common spaces (this can typically take up to 15% of the total CO₂e emissions).

There are numerous ways that common areas can be reduced:

Space efficiencies can also be gained by increasing the number of stairwells whilst reducing the common walkway areas.

Although stairs are likely to be the more expensive option, this could be recouped by adding the spare hallway space into each apartment, in the example above this provides an extra 8.75m2 per apartment.

Typology (Beds and bathrooms)

Environmental impacts can be reduced through increasing the occupancy of the apartments themselves. Whilst 2 bedroom 2 bathroom apartments are fashionable, with good design that (rarely used) spare bathroom could be a third bedroom instead. This provides an increase in the overall sustainable living space of the building without impacting on the floor area being constructed

 Materials

In many ways embodied carbon is equally (and perhaps more) important a consideration than operational energy. eTool LCAs will typically assume current grid intensities throughout the 100+ year predicted design life of a building. This means operational energy makes up around 80% of the total impacts. In reality over the next 100 years the grid will decarbonise and operational energy will contribute much less over time. The embodied carbon in materials on the other hand is locked in from the year the material is manufactured and transported to the site. There are many low impact alternatives to common materials in construction. Timber and CLT can be used in place of concrete and steel. Where concrete is necessary fly-ash or blast furnaces slag blends should be incorporated, these are waste products that can directly replace a proportion of the concrete thereby reducing its impacts.

Timber veneers and plywood should be avoided due to the high impact of the glues and resins used in these products. Plasterboard also has very high impacts. Alternatives such as plain hardwood, bamboo or MDF represent significant savings. IF plasterboard is to be used 6mm sheets should be preferred to 12 mm sheets with acoustic requirements met through insulation which is typically low in CO2e emissions.

Carpets (especially wool) should be avoided with cork or polished concrete finish preferable. If absolutely necessary carpets should be dark coloured (to avoid replacement through soiling) and plant based materials such as jute and sisal should be specified that have natural/non-synthetic rubber backing.

Lighting

There tends to be little difference in terms of environmental benefit between CFL lights and L.E.D lighting Increasing natural light levels using solar-tubes, skylights or similar means less use of artificial lighting energy. Specifying lighter matte colours to surfaces such as the balcony, ceiling and walls will bounce light deeper into the dwelling thus increasing natural lighting. Light shelves in windows is another passive way to divert and bounce light deeper into the dwelling. Similar systems using adjustable louvres can also be used. Providing translucent shading material in addition to heavier curtains allow the option of diffused daylight to penetrate whilst maintaining privacy. The top of the windows is where light penetrates deepest into the dwelling, so it is important to ensure that this part of the window is not obstructed by drapery or blinds. Translucent partitions between rooms also allow light to be drawn into deeper rooms. Clerestory windows also provide a method of introducing more natural light into central rooms.  Ideally these should be utilised with higher ceilings and high reflectance surfaces in order to encourage light to penetrate.  In order to prove the value of these initiatives a daylighting simulation should be undertaken to ensure expense is not incurred for no benefit.  This will likely make this recommendation hard to justify economically (there will be many far easier wins elsewhere in the building.

Gas cookers over electric

In regions with fossil fuel dominated electricity grids such as WA, gas represents a large advantage over electricity for providing energy to cook with.  This is due to the heat and electricity losses associated with distributed power.  Burning the fuel (gas) at the source eliminates these losses and is a more efficient way of using the fuel. The majority of gas cookers sold today include safety features that automatically turn off the gas when no flame is present. Rinnai has also developed the ‘inner flame’ technology that produces a flame that is directed inwards which is about 27% more efficient than standard gas stoves. The drawback to moving to gas cooking is that a gas pipeline may need to be installed. If the implementation of this strategy is outside of the project budget the developer may offer the strategy as an upgrade package for purchasers. This eliminates the need for upfront capital while promoting best practices and educating the public.

Or Induction cooktops

An all induction cook-top is an alternative that could deliver carbon savings over a standard electric cook-top.  Induction cook-tops work by transferring electrical energy through induction from a coil directly to the magnetic pan. Only the area in contact with the coil heats up and therefore the cooker can be up to 12% more efficient than a standard electric conduction cooker.  The controls on an induction cooker are also far more precise giving a greater range of cooking techniques.

Car Park Ventilation

By applying a detailed engineering design to the car park ventilation systems, it is expected that the fan run times could be considerably cut down especially when natural ventilation is utilised.  Computational fluid dynamics would be utilised in this technique to determine how to best move air through the car park to maintain acceptable CO2 levels with minimum energy demand.  Gains may also be achieved in reduced ducting.  At least a 20% saving in ventilation may be achieved.

Biodigesters

Biodigesters turn food and or human waste into gas that can be used in cooking. Although not well established in western countries this technology has been used for hundreds of years in China and India. Communal or individual systems exist that may be incorporated into an innovative building design.

 Appliances

The appliances that go into the building can make a significant proportion of the recurring impacts.  Modern appliances tend to have fairly small warranty periods in relation to the lifespan of a building.  TVs in particular can often not last more than 10 years.  Ensuring that appliances are purchased second hand and those that are purchased new have a long warranty and are kept for as long as possible can provide significant carbon savings.  In this recommendation we have assumed each appliances lasts twice as long as the standard warranty. Where appliances are installed they should also be of the higher MEPS rating bands for energy efficiency.

Thermal Performance

Modern 6 star dwellings in Western Australia need very little in the form of heating/cooling. The developer with sustainability in mind will provide only ceiling fans for cooling and renewable biomass pellet heaters for heating. Bio Where air conditioners are provided they should be single split units which can obtain higher efficiencies generally than multi splits. A COP/EER of 5 is exemplary.

Tri-generation, deep geothermal and shallow ground source heat pumps can also be appropriate in very large developments with high demands such as precincts with swimming pools. However they entail very high outgoing capital costs and the environmental benefit should be considered carefully against other technologies.

Swimming Pools

Most importantly swimming pools should be appropriate for the size of the development. Proportionally 50m2 pool shared amongst 100 dwellings will have 100x fewer impacts per dwelling than the same size pool provided for a single dwelling. Where pools are installed they should ideally be naturally heated through ambient air and install pool covers that contain the heat when the pool is not in use. Typically including a pool cover which can operate automatically or manually for 8hrs per day during the pools closed hours has a 28% saving in the pools heating energy demand. Pool pumps efficiency should also be considered carefully, high-efficiency pool pumps of up to 9 stars MEPs rating are currently available on the market.

 Hot Water

Alongside solar thermal technology and low flow shower heads, an opportunity exists to warm the inlet temperature of the water by using a heat exchanger. Water exiting apartments in the sewerage drains will have a higher temperature than the normal inlet temperature of water coming into the building from the mains, particularly in winter.  By passing the inlet water over the warmer outgoing water, the temperature can be increased. A 5% reduction in energy demand of the hot water system can be achieved.

For communal systems there will be significant heat losses in the pipe carrying the hot water around the building as well as from the individual water storage tanks. Based on the conservative assumptions of a 25mm pipe with 25mm of insulation (125mm total diameter) the heat losses are estimated to increase the hot water demand by 10%. Correctly installed 50mm pipework insulation could therefore reduce the losses through hot water pipe by approximately 5%.

eTool

The door is always open at eTool for questions surrounding design decisions. If a project is in concept phase we are happy to sit down for an hour and discuss potential strategies and targets. Full targeting sessions are also available at low cost to determine more accurately the costs involved in achieving design aspirations. Following this our full LCA will provide the most detailed environmental assessment available.