Get the Building Shell Right
Like your favourite clothes the outside of your home (building shell) has to be stylish, keep you dry, comfortable, and protect you from the elements
A building shell is what separates the interior and exterior of your home. It helps facilitate climate control and protect the indoor environment. Overall it is the entire exterior building system. It includes doors, windows, roof, foundation, floor, cladding and all the components such as structural masonry and insulation.
Here are some of the key elements of the building shell you should think about.
Building Materials
The materials that you choose to build your house with affects more than appearance. It can also have a big impact on comfort.
Brick and timber framing with cladding are the most common walling systems. Bricks are referred to as having high thermal mass because they are dense and hold their temperature, whereas timber framed walls with cladding are referred as light weight and have low thermal mass so don’t hold their temperature. SIPS (Structural Insulated Panels) are also light weight and have low thermal mass.
In cool and temperate climates, including high thermal mass internal walls made from brick (or other dense material) can help to stabilise the temperature, especially if the house is designed to capture northern winter light to warm up the mass, and have good cross ventilation to cool down the mass in summer. In hot climates, light weight walls are preferred because they don’t hold the heat. The same principles apply to flooring. Concrete floors with a polished finish or tile covering provides a good source of thermal mass and will hold warmth when exposed to sunshine, whereas timber boards and carpet floors won’t.
The properties of building materials and how they impact the comfort of a home is an important consideration and can be assessed during the design phase as part of a home energy assessment.
Insulation
Insulation reduces the movement of heat in and out of a house, helping to keep it warmer in winter and cooler in summer. It’s one of the most cost-effective ways to make your home comfortable.
The most common form of insulation is bulk insulation such as ceiling batts. These work by trapping air between the fibres, making it a poor conductor of heat. Bulk insulation batts are also used in framed walls. Another common form of insulation is reflective insulation which reflects radiant heat. The two are often used together achieve the desired insulation performance in the roof and ceiling, as well as the walls. In cold climates, insulation is also commonly included under the floor, whether this be under (or within) the concrete slab, or under floorboards.
The Building Code of Australia sets out minimum insulation requirements for the various regions around the country. Optimum insulation should be considered during design phase as part of a home energy rating assessment which takes into account other related factors such as climate zone, building orientation and materials.
Windows
Did you know up to up to 40% of a home’s heating energy can be lost and up to 87% of its heat gained through windows!
With up to 40% of heating and cooling energy being lost through windows, the size, position and glazing type of windows play a key role in the comfort of your home.
Thoughtful window placement can help to naturally warm and cool a home through capturing winter sun and cooling summer breezes, with their position informed by the orientation of the house. Glazing type is also important to help reduce the uncontrolled transfer of heat.
Standard glass is a very poor insulator which means the heat moves through it very easily. On a hot day it will flow into your house, and on a cold day it will flow out of your house. Double glazing provides a big improvement on this. It’s made with two sheets of glass, with an inert gas in between, sealed within the frame. This acts like insulation by slowing the movement of heat across the windowpane. Double glazing is particularly valuable in cool climates and in the main living zones of the house where the inclusion will have the biggest impact on your comfort.
Curtains also make an effective, low-cost insulation for windows – especially to keep heat from escaping in winter. They can be opened during the day to allow light in, and closed at night to keep the warmth in.
Just like insulation, windows and glazing type should be considered during the design phase as part of a home energy assessment to optimise the comfort of your home.
Air Tightness
Air tightness refers to how well sealed your home is, with the aim of reducing unwanted heat loss through draughts. A well-sealed home will also have less dust, less insects and less noise entering from outside.
Air leakage can account for up to 25% of heat loss from your home, with the main leaky points being poor seals around doors and windows, gaps around light fittings and other ceiling penetrations, and unsealed exhaust fans. Leaky gaps can also occur between wall, floor and ceiling junctions, and around window frames.
Inspections and tests can be undertaken during the building process and at completion to eliminate common causes of air leakage, with the results verifying the quality of construction. This should be discussed with your builder early in the design process to ensure you are getting the quality build you’re paying for.
Shading Controls
Preventing unwanted sun from entering your home in summer through shading is one of the most effective ways to make it comfortable and reduce air conditioning costs.
When sunlight enters a window, heat gets trapped inside the house. This can be an advantage in winter but will quickly lead to overheating in summer. Shading devices such as pergolas, shade sails, louvers or even deciduous trees and vines can be used to block unwanted sun. In cool and temperate climates, shading devices on the northern side of the house need to be adjustable, or designed to allow in winter sun, whereas shading devices on the east and western side can be more permanent.
External blinds are also an effective shading device but will reduce the amount of natural light entering the home. Internal blinds are less effective as once direct sunlight enters through windows it becomes trapped as heat.
Shading controls can also be used to shield walls and paved are as around the home for improved comfort. Protecting these surfaces from direct sun in summer reduces heat build-up and the amount of heat that may transfer into your home through windows, air gaps and other week points.
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