Designing Comfortable Homes - Part 4

If you’re thinking about building a new home, there are some important design elements to consider that are key to making it comfortable and energy efficient. Homes can be naturally warm in winter and cool in summer if they are built with the appropriate combinations of glass, thermal mass and insulation.
 
This is the fourth of a series of excerpts from Designing Comfortable Homes featured in five editions of How To. The series will cover the three principles of passive solar design that follow the path of solar heat gain through the house. It starts with heat collection that allows the sun’s heat to enter the house, moves onto heat storage to keep this heat and concludes with heat containment, which traps heat in the house.
 
The publication in full is available for free download from www.ccanz.org.nz
 
Air tightness
 
There is a link between building complexity and energy performance. More complicated designs with more construction joints tend to have more uncontrolled air leakage – technically known as infiltration – which can have a major impact on heating energy requirements. These leaks can be in the construction materials (for example, weatherboard exterior cladding and timber floorboards are inherently leaky) or they can result from the complexity of the plan itself (for example, corner joints, joints for cladding changes). The main ways to deal with these are:
 

• Use sheet materials, or materials mortared together like brick or concrete walls, which have fewer inherent leakage properties.
• Simplify the design to have less potential air leakage sites (e.g. fewer corners).
• Take extra care during construction to seal all corner joints against air leakage.
• Ensure penetrations in cladding or lining for plumbing or electrical fittings are well sealed.
• Where design and construction still allow possible air leakage, air tightness barriers could possibly be used.

 
For a well-constructed, well-insulated house, air leakage accounts for around 20-25% of the space heating energy use, so any reduction in heat loss from air leakage will have a significant benefit. Wind causes heat loss both through air leakage and by increasing the conduction heat loss, particularly through windows. There are therefore two primary ways of dealing with these heat losses:
 

• Ensure the house is well sealed; both its construction joints and by weather stripping windows and doors.
• Use external wind breaks to reduce the impact of the wind on the house (these have the added advantage of making outdoor areas usable more often).

 
These should be used in combination. Weather-stripping can't deal with increased heat loss by conduction through the glass itself because the wind strips away the heat from the outer surface. Wind breaks can reduce this heat loss but on their own only partially solve air leak problems that weather stripping addresses.
 
Using plan and site layout to improve comfort
 
There are many considerations that will influence the plan layout for a house – the site topography, the orientation to the sun, the views and your likes and dislikes, to mention just a few. There are some simple layout guidelines to improve the energy efficiency and comfort of your home. It may not always be possible to follow these guidelines completely because of constraints and preferences relating to other design considerations. However, an understanding of these simple guidelines will help you make informed decisions about the trade-offs that are an integral part of any design process.
 
Size and shape
 
Designing a house that is rectangular, so the north-facing facade is larger than the east or west facades, increases solar gain when it is most needed. It is also the easiest to control with simple shades when solar gain needs to be reduced. The small east and west sides also mean there is less potential for overheating and glare from low-angle sun.
 
Making the building rectangular makes the plan less deep, so that cross ventilation for cooling is easier to achieve. Also, making the plan less deep from north to south makes it far easier to distribute the heat from the north-facing rooms to the other less sunny parts of the house.
 
The heating and cooling requirements of a house are directly related to its size. You should think very carefully about how much space you really need if you are serious about comfort and energy efficiency. If you build a house that is twice the size you need, it will cost you roughly twice as much to heat and cool.
 
Wind contributes to heat losses
 
Wind can have a major impact on heat loss from a house. A house located on top of a ridge can have heat losses 50% greater than if it were on the flat.
 
Next issue: Avoiding over-heating