Eco-friendly builds are becoming universal, but how would you design a property for maximum energy efficiency and minimum carbon impact?
We all understand the importance of designing homes for maximum energy efficiency. In fact, some people aim for zero energy homes, designed from the ground up to be so super-insulated, energy efficient and renewable that they have a minimal running cost and carbon footprint. It’s even possible to design a zero-carbon home – a challenging prospect, but see https://zeroenergyproject.org for some pointers.
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But it is possible to create a less demanding but still energy-efficient home, particularly if it is a self-build and you have control over the specification.
The concept is often referred to as the ‘Passivhaus’ philosophy.
The Passivhaus concept originated in Germany in the 1990s, and aims to reduce vastly the energy usage of homes by focussing carefully on the design and construction stages. It’s more about this phase than the fancy technological energy-saving gadgets you may choose to fit later – the argument is that if you get the fabric of the building right, your eventual energy usage will be minimal.
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Design and build
The Passivhaus concept works in two stages, design and build. In the Design stage, the emphasis is on radically reducing air leakage, the major source of heat loss in conventional builds.
The main ways to do this are to increase insulation levels, make good use of glazing for heat gain, and to eliminate thermal bridges. A thermal bridge, also called a cold bridge, is an area of a building construction with a significantly higher heat transfer than the surrounding materials, typically where there is a break in the insulation, or the insulation is penetrated by an element with a higher thermal conductivity, such as timber.
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Achieving Passivhaus status depends very much on the construction team working closely together – each stage could involve a costly mistake if it isn’t well planned.
Several types of construction including timber frame, structural insulated panels, insulated concrete formwork and cross-laminated timber are applicable for achieving a high level of air tightness, and less efficient methods, such as Brick and Block, can have their airtightness levels improved by using special tapes and membranes.
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After basic construction the next essential in the Passivhaus philosophy is a high level of insulation. Retaining warm air is the key to lowering heating costs and your carbon footprint. Another common element of a Passivhaus design is triple-glazing.
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“There have been some incredible developments in glazing technology over the last few years, particularly in the use of triple glazing, which can regulate solar gain and increase thermal comfort, as well as limiting noise. But triple-glazing is still around 10-15 percent more expensive than a double-glazed performance window, so unless you specifically need it, as in a Passivhaus design, you might well get a better balance between cost and performance from high-performance argon- or crypton-filled double glazing units.”
Fabric first
This ‘fabric first’ approach before thinking of other energy-saving measures is increasingly common in new builds, even if the aim is not to achieve full Passivhaus certification. If that is the aim, to complete a certified Passivhaus you must engage a Certified Passivhaus Designer, a specialist in designing and certifying the standard. our house. This will be an additional professional cost to your project and may cost around £5,000.
The Passive House Planning Package (PHPP) is a design tool produced by the Passivhaus Institut for use by building architects and designers. PHPP incorporates the energy specifications for quality-approved Passivhaus buildings from the Institut in a manual and CD-Rom. PHPP contains a series of tools for:
- Calculating energy balances
- Designing comfortable ventilation
- Calculating the heat load
- Summer comfort calculations
The latest version of the software, PHPP 9, is now available, offering many benefits over its predecessor. PHPP 9 includes facilitated data entry and incorporates the latest results on the integration of renewables in building energy concepts.
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It also includes further findings from the Passivhaus Institut’s recent research on high performance buildings in various regions in the world; additional calculations combined with newly validated algorithms ensure suitability for all climates, including those with cooling and dehumidification requirements.
Suitable for both residential and many non-residential applications, PHPP is supported by Certified Training Courses to help you get the most from the software.
So what can you do if you are working not on a new build but on an existing, and possibly very energy-inefficient, house? Some of the Passivhaus methods can be applied here through a less-demanding standard called EnerPHit, devised by the Passivhaus Institut specifically for retrofit projects. Find out more about it at www.passivhaustrust.org.uk.
Eco-friendly builds are becoming universal, but how would you design a property for maximum energy efficiency and minimum carbon impact?
This feature was first published in Property & Home With Martin Roberts, Winter 2020 – read more here.
