There are several smart ways to keep your home comfortable all year round.  The two most common ways of becoming energy efficient are installing double-glazing and insulation.  These are also an integral part of your home’s building envelope, which is made up of the ceiling, floor and external walls.

Although critical, these features don’t give a complete picture of the efficiency of a house. Even with these expensive building elements, envelope air leakage into the building must be tackled. 

The air inside your home, with its heating or cooling energy contained in it, always moves through a building envelope and escapes to the outside. This air movement is caused by holes and gaps in air conditioning duct work, walls, ceiling and floor systems, exacerbated by air pressure difference between inside and outside. The holes and gaps are often small, but there are 100’s of them throughout your home: power points and switches on external walls, gaps under skirting and around window architraves, attic access, ceiling exhaust fans, down lights, to name but a few.

 

A pressure difference can be created through several factors, most often the wind blowing against your house, an exhaust fan in the bathroom, or a leaky ducted system throughout the house.

The result of all this air movement is expressed as an air leakage rate or in air changes per hour (ACH). For example, if your home has one (1) ACH at ambient pressure, it means that total volume of air in your house has been replaced by outside air once every hour, even with little or no wind blowing outside. If the wind picks up, the ACH of a house multiplies many times.

ACH50Natural Air ChangeRating% of bill% saving potentialVentilation Requirements
1.5.075Super2%noneConstant energy recovery ventilation
3.5.18Excellent6%1 to 3%Occasional forced ventilation
5.25Better10%2 to 4%Occasional
7.35Good14%2 to 5%Small
10.5Fair20%3 to 10%Rare
201Bad40%5 to 20%Little to none
StandardHouse Leakage based on floor area of: 210 square metres
ACH50
PassivehausPassive House.6
CGSB149.1Canadian R-20001.5
ATTMA TS-1UK, Best Practice, residential
3.4
Oregon3.5 to 5 is Tight, great
3.5
ASTM E779LEED, 1.25 sq in at 4 Pa / 100 sq ft. Envelope
4.7
PA HousingTight < 5 Housing Research/Resource Center (PHRC)
5.0
EEBAEnergy and Environmental Building Association Guidelines
5.2
EN13829Most European countries
6.1
Oregon5 to 7 is good
7.0
PA HousingModerate < 10, Leaky > 10 Housing Research Center
10.0

The following graph explains the relationship between wind speed and the pressures it creates on the building envelope. To test the air leakage of a building, a pressure difference of 50 Pascal (Pa) is applied. This test is performed through the use of a ‘blower door’, a mechanical device designed to determine the air tightness of a building envelope.

Air leakage testing at a pressure difference of 50Pa is an internationally accepted standard. If for example, the building leaks at a rate of 10 ACH at this pressure, it is expressed as 10ACH at 50 Pa. As seen in the graph, a 50Pa pressure difference is comparable to a wind speed of 32 km/h blowing against the building, while a 1.5Pa pressure difference is equivalent to a 5km/h wind.

Once you have made the decision to address the air leakage of the home, the question then becomes how (air) tight the building should be. If it’s too tight without proper mechanical ventilation, it will impact the indoor air quality. But if it’s too leaky, it will affect the energy efficiency. Here is where an air leakage test can provide the answer. Not only will this test give you an ACH at 50Pa of your home, but it will also pinpoint all of the invisible holes and gaps.

Another useful diagnostic tool in this testing process is the thermal imaging camera. This camera can pick up temperature differences in a building envelope, as well as show where insulation in the wall or ceiling is missing.  If 5% of the building is not insulated correctly, the overall efficiency of the insulation drops by roughly 35%! Therefore, it is important to have a continuous insulation barrier for the whole house.

If after sealing, the ACH of your house drops below 10ACH at 50Pa, a well thought out ventilation strategy should be implemented. One such strategy is the installation of a mechanical whole house ventilation system, which introduces tempered fresh air to the living and bedroom areas, and removes stale, moist air. It is important to make sure that exhaust fans in kitchen, bathroom, and toilets can do their job, by allowing sufficient make-up air to be introduced back into those areas of the house. Poorly running exhaust fans are more than often the cause of mould and mildew.

In most cases, however, a building envelope can be sealed to the right level and thus provide a balance between energy efficiency and healthy indoor air quality.

There are many benefits of having a well-sealed building envelope: It makes the house substantially more energy efficient and comfortable, reduces moisture issues (mould!), and keeps dust, insects, and noise out. Compared to double glazing and extra insulation, sealing your home is extremely cost efficient and relatively simple to do. It is an investment with a substantial payback and can represent in many cases a 25% reduction in the overall energy cost.

Now for the most important question: How energy efficient is you home?

Contact us Efficiency Matrix, for an appraisal of your home…

210 square metre home with basement
ACH50
Excellent- Less than 5%
1.5 - 2.0
Good- Best 30%
2.5 to 5
Poor- 55 %
5 to 10
Very bad- 10%
10 +

 

By Jan Brandjes