Airtightness of the building envelope is critical to high performance.
Stopping draughts is only part of the reason for striving for this objective. Getting control over heat flows in and out of the building, managing ventilation for the best indoor air quality and controlling moisture flows whilst still allowing breathability are part of this approach to quality in the construction process.
This appalling revelation from the UK about the legally allowable draughtiness of new homes reflects the lack of regulation in Australia and the imposition of unnecessary energy costs upon new home owners over the whole life of the building.
Encouragingly, the solution is clearly mapped out. We just need awareness & willingness to improve construction processes to achieve the Passivhaus standard across the industry.
HOW IS AIRTIGHT TESTING DONE?
Today, many builders are routinely building houses that are very airtight, often without realizing it. The common use of building wraps, moisture barriers, high efficiency windows and even simple plywood sheathing all have direct effects on reducing air leakage and infiltration. An airtight house has many fewer openings through which fresh air can enter. Without the addition of mechanical ventilation, a tight house can result in stagnant air, less natural ventilation and dissatisfied homeowners. On the other hand, houses with large amounts uncontrolled air leakage are equally troublesome with comfort complaints due to drafts, building failures and high energy bills.
Despite the growing importance of house airtightness, few builders, architects or homeowners know how tight their houses are. Until recently, the building community has tended to rely on subjective estimates of airtightness. Unfortunately, it is impossible to accurately estimate the tightness level of a building by visual inspection alone. And without knowing the airtightness level, it is difficult or impossible to design for effective approaches to ventilation and air quality, or to accurately diagnose performance problems.
WHY IS BUILDING LEAKAGE IMPORTANT?
Building tight houses without providing proper ventilation can increase the potential for health and safety problems to occur. Higher moisture levels found in inadequately ventilated houses create an ideal environment for moulds, dust mites and other causes of respiratory problems and allergies. Tighter houses are also more likely to experience problems from back drafting and spillage of combustion products from naturally drafting furnaces, water heaters and fireplaces. This is because in tight houses, it is easier for exhaust devices (e.g. dryers, kitchen and bath fans) to create large pressure differences between inside and outside of the house, which can interfere with proper venting of the combustion appliances.
Leaky houses have their own set of problems ranging from drafts, blistering paint, ice dams and frozen pipes to a house that won’t adequately heat or cool. While in the past air sealing efforts concentrated on the easy to find air leaks around windows and door, we now know that the most are responsible for most of the air leakage in typical houses and are often the cause of performance and durability problems.
And whether a house is tight or loose, nothing will cause it to deteriorate faster than moisture migration and condensation in attics, ceiling and other building cavities. Vapor barriers will stop moisture diffusion, but most moisture problems in buildings are a result of uncontrolled air leakage through the building envelope. And the way most vapor barriers are installed, they do little or nothing to stop uncontrolled air leakage. In many buildings, moisture problems are made worse by important leaks in a house are the hard to find leaks in the attic, crawlspace, attached garage and other framing connections. These hidden leaks the common use of hot tubs, whirlpools and saunas.
Measuring Building Airtightness
The easiest way to measure building airtightness is with a diagnostic tool called a blower door. The blower door consists of a powerful, calibrated fan that is temporarily sealed into an exterior doorway.
The fan blows air out of the house to create a slight pressure difference between inside and outside. This pressure difference forces air through all holes and penetrations in the building envelope. Blower door tests are typically performed at a pressure difference of 50 Pa (0.2 inches of water column).
By simultaneously measuring the air flow through the fan and its effect on the air pressure in the building, the blower door system measures the airtightness of the entire building envelope. The tighter the building (e.g. fewer holes), the less air you need from the blower door fan to create a change in building pressure.
Airtightness measurements are presented in a number of different formats including:
- square meters of leakage area
- air flow needed to generate 50 Pa of pressure difference (m350)
- air changes per hour at 50 Pa of pressure difference (m350)
In addition to assessing the overall airtightness level of the building envelope, the blower door can be used to estimate the amount of leakage between the conditioned space of the building and attached structural components such as garages, attics and crawlspaces. And because the blower door forces air through all holes and penetrations, these problem spots are easier to find using chemical smoke, an infrared camera or simply feeling with your hand.
Finally, blower door measurements can be used to estimate the natural infiltration rate of houses. While the blower door doesn’t measure infiltration rates directly, test results can be used along with mathematical models to estimate annual average and design infiltration rates for the purposes of evaluating indoor air quality, the need for mechanical ventilation, and to help with proper sizing of heating and cooling equipment.
PASSIVHAUS PERTH have a MINNEAPOLIS BLOWER DOOR and a DG 1000 pressure and flow gauge available for testing throughout Perth and WA.
The Minneapolis Blower Door has long been recognized as the best designed and supported building airtightness testing system in the world. Combined with specialized accessories and testing procedures developed by The Energy Conservatory, the Minneapolis Blower Door is the system of choice for utility DSM programs, energy raters, HVAC contractors and weatherization professionals. Complete with everything needed for fully automated Blower Door testing. Built-in Cruise Control allows us to automatically control the Blower Door fan to maintain a constant 75 Pa, 50 Pa, 25 Pa or 0 Pa building pressure without having the gauge connected to a computer. Precise, stable flow measurements without the need for gauge dampening. The Model 3 Fan provides quick and accurate flow measurements from 300 to 6,300 CFM (includes Flow Rings A and B). Optional Flow Rings C, D and E will measure down to 11 CFM. Variable fan speed control (solid state – cruise control compatible). Both 110V/60 Hz and 220V/50 Hz models. This Model 3 Minneapolis Blower Door system includes a single fan, the DG-1000 pressure and flow gauge with Cruise Control, and the adjustable aluminium frame and nylon panel.
The innovative design of our adjustable aluminium frame and durable nylon panel is the result of years of refinements based on the experience of thousands of users. There is no easier way to seal a Blower Door fan into a door opening. Snap-together aluminium frame comes in a compact carrying case and sets up in seconds. Precision engineered cam lever mechanism securely clamps the nylon panel into the door opening. Adjusts to fit the largest and smallest residential door openings. A built-in window allows us to monitor outside activity.