Sustainable Design That Pays: Measures Worth Their Cost

Some environmental measures return their cost and some do not. Which ones make sense in this climate.

Sustainability in buildings is discussed either as a moral question or as a marketing term. Treated practically, it is a set of measures with costs and returns that can be compared, and in a cooling-dominated climate some of them return their cost several times over.

What this number does and does not include

This covers measures affecting the energy and water performance of a house. It excludes certification schemes and the documentation they require, which have their own cost and purpose.

Envelope insulation

Reducing heat gain through walls and roof, which is the dominant load in this climate.

• Pushes it up: Higher specification, and retrofitting rather than installing during construction.
• Brings it down: Installing during construction, where the marginal cost over no insulation is modest.
• How to control it: This is the highest return measure available. It costs little during construction and reduces cooling for the life of the building.

External shading

Preventing solar gain before it reaches the glass, through building form or added elements.

• Pushes it up: Bespoke shading devices and complex geometry.
• Brings it down: Integrating shading into the building form, where it costs little beyond the design attention.
• How to control it: Shading designed into the form is close to free. Shading added as a device costs more and still outperforms high specification glass alone.

Glazing specification

Controlling heat gain and loss through windows, which are the weakest part of the envelope.

• Pushes it up: Large glazed areas requiring high performance specification to compensate.
• Brings it down: Proportionate openings with shading, which reduces the specification needed.
• How to control it: Reduce area and add shading before increasing specification, since both are cheaper routes to the same result.

Efficient cooling equipment

The equipment that consumes most of the building's energy over its life.

• Pushes it up: Oversized systems, poor installation and equipment selected on price alone.
• Brings it down: Correctly sized equipment with efficiency considered against its running cost.
• How to control it: Compare equipment on running cost over its expected life rather than on purchase price, since the difference is usually decided within two years.

Water efficiency

Fittings and irrigation that reduce water consumption, which matters both environmentally and in running cost.

• Pushes it up: Extensive landscaping requiring irrigation.
• Brings it down: Efficient fittings, which cost little more than standard ones, and climate-appropriate planting.
• How to control it: Specify efficient fittings as standard, and design landscaping around plants that survive the climate with limited irrigation.

Solar generation

Photovoltaic generation, which converts roof area into electricity.

• Pushes it up: Larger systems, complex roof geometry and storage.
• Brings it down: Simple roof arrangements and systems sized to actual consumption.
• How to control it: Assess against your consumption pattern and the applicable arrangements for generation in your area, since the return depends on both.

Costs that never appear on the first page

• Maintenance of systems that require servicing to maintain performance.
• Replacement of components with shorter lives than the building.
• Performance that falls short of projections when installation quality is poor.
• Certification costs where a formal scheme is pursued.

Keeping the budget honest

Prioritise measures in order of return: insulation and shading first, then equipment efficiency, then generation. The passive measures cost least, last the life of the building and require no maintenance, which is a combination the active measures cannot match.

• At concept, when form and orientation can still respond to climate.
• When the envelope specification is set.
• When cooling equipment is selected, comparing running costs.
• Before roof design is finalised, if generation is intended.

If you are starting a design, Domira can help you write the brief, review the drawings and keep the design aligned with the budget before it reaches a contractor.