Chapter 5 Rural Housing Guidebook – Thermal Performance vs Traditional forms

Now, this is going to be a juicy section; how can we marry an energy efficiency with a design that the planners (and clients) are happy with. Interestingly enough, rural Irish forms are a perfect fit for energy efficiency – the areas that I’ll be looking at in this and subsequent posts are:

  • Requirements
  • Form
  • Size
  • Details
  • Insulation
  • Airtightness
  • Glazing
  • Materials
  • As any regular reader will know, I am a big proponent of the Passive House (Passivhaus) standard and I think it’s a no-brainer that this is what all housing should be achieving; imagine living in a house that after a hard winter your fuel bill is so low that you don’t need to bat an eyelid. It makes complete commonsense to think along these lines now that we have the knowledge, technology and ability to design and build houses that have minimal energy consumption.

    I’ll be feeding in a few Passive House concepts as we go but this first post is concerned with an ideal, energy efficient form versus what would also be considered an acceptable, suitable form for the countryside. And as mentioned above, the good news is that (in my opinion) the form put forward as acceptable in the Irish countryside is perfect for a Passive House.

    Traditional energy concepts are that thinking of the house as a heat exchanger, it follows that the greater the building’s volume – the more surface area it has to lose or gain heat from. Therefore to conserve heat you should think carefully about the surface area:volume ratio. Therefore, the more compact the form, the more efficient the house is as a heat exchanger. The diagrams and figures below have been redrawn from ‘EcoHouse 2 by Sue Roaf: ISBN:0 7506 5734 0, (originally published by A. Krishan Climatically Responsive Energy Efficient Architecture – a Design Handbook)

    Buildings with different perimeter:area ratios

    Buildings with different perimeter:area ratios

    The figures give the surface area:volume ratio, as you can see the form with the best area:volume ratio is the circle.

    The problem arises (especially with increased temperatures worldwide) that a building with a sprawling form can dissipate heat better in a warmer climate. Part of the PHPP calculations include a section for including shading devices such as balconies and brise soleils for example. Immediately you can see a conflict with the more compact forms.

    It should also be remembered that a compromise between the two examples given above, say a longer rectangular form; allows for cross ventilation when the building is a single room deep, better light penetration for the same reason and the ability to have a maximum number of habitable spaces facing south. Even if the building extends beyond a single room depth; you can place narrower depth rooms that require less light (such as bathrooms, utility rooms, corridors etc…) on the northern side of the building.

    Traditional cottage

    Traditional single room deep Irish Cottage

    We can therefore see that the traditional Irish forms of the cottage, Irish long-house and even courtyard type designs fit the above example well. The next post/section will show how these simpler, bold forms (albeit of a narrow depth and when they are carefully detailed) are also easier to construct to ensure an airtight fabric – another key element of an energy efficient and Passive House construction…

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