The numbers are in (2)
Part 2 of a 5-part series in which we quantify the value the Flexi House system can provide Kiwis looking to build. This blog explores the airtightness we achieved in Cromwell and why it is important.
At Flexi House, we’re helping Kiwis break free from the bare minimum by building airtight envelopes.
How airtight? 1.29 ACH to be exact.
A pre-line blower door test of our Cromwell Show Home carried out during construction by Pro Clima resulted in a measurement of 1.29 air changes per hour. This is at least 2-3 times more airtight than a typical new build, which would be 3-5 ACH.
Hang on a minute, what’s a blower door test?
A blower door test is used to determine how airtight a building envelope is. It is commonly performed in high-performance homes and buildings looking to achieve Passive House certification to assess air leakage against set criteria.
To measure airtightness, a specialised fan called a blower door is installed in a doorway of the building envelope and sealed to the frame with a canvas screen. The fan is used to create a pressure difference between the inside and outside of the building. The envelope is pressurised to 50pa and then depressurised to 50pa. By measuring the airflow through the fan at these pressure differentials, the test can determine the air leakage rate of the building. The average air changes recorded for pressurised and depressurised are used to determine the ACH, or air changes per hour.
The blower door test helps identify areas of air leakage, which can contribute to energy loss, discomfort, and reduced indoor air quality. It is an effective method to locate and quantify air leaks and can be used to prioritise air sealing efforts in order to improve energy efficiency and reduce heating and cooling costs.
During a blower door test, smoke pencils or thermal imaging cameras are typically used to visually locate air leaks. By walking around the Flexi House with burning incense sticks, we were able to see where there were holes that needed to be patched up by the direction and speed of the smoke trails.
The Passive House threshold is 0.6 ACH, which means that 60% of the air inside the home is replenished every hour. A typical new build in New Zealand is anywhere from 3-5 air changes per hour. This means that all of the air inside the home would be completely replenished every 12-20 minutes at 50pa. Imagine how much energy you’re using to heat air that is only around for quarter of an hour!
But wouldn’t it get stuffy?
Sure, without mechanical ventilation it would!
Once we have control of the airspace, we’re able to condition it as necessary. The Flexi House Show Home uses the Lunos Nexxt decentralised Mechanical Heat Recovery Ventilation unit to do just this. It’s a slim panel on the wall that brings fresh air into the house and transfers the heat from the outgoing air to the incoming air at up to 90% efficiency. This means that the heat pump doesn’t need to do so much work conditioning fresh air.
Airtightness is important because being able to control the air inside your home makes it more efficient to heat and cool. It’s a critical consideration for an energy-efficient home.
Does this mean I can’t open windows then?
Natural ventilation is unreliable, but that shouldn’t stop you from opening windows. Just make sure they’re all shut before you turn the heat pump on to use the least amount of energy to heat your space.
Your home should be able to look after itself, and you shouldn’t have to open windows in the middle of winter to ventilate it. High-performance homes use mechanical ventilation that maintains indoor air quality and comfort within the home. Your home can be well-ventilated AND efficient to heat or cool all year round using Mechanical Heat Recovery Ventilation (MHRV).
So how do I create an airtight home?
The Flexi House was able to achieve such a low air-change rate by using Pro Clima Intello Vapour Check. This is a membrane that is stapled to the framing and taped to seal all holes. We also made sure to tape the joins between our floor panels to stop air coming in through the floor.
One improvement we’re making to further increase the airtightness in our buildings is using uPVC glazing units. These are designed to European standards with airtightness in mind and aren’t as leaky as aluminium glazing. Sliding units are noticeably more leaky due to their brush seals, as opposed to rubber seals used for awning or tilt-turn windows.
But don't just take our word for it! You can feel the Flexi difference for yourself. If you're in the area and want to visit the Show Home, get in touch and we'll arrange a time for a tour! As the Flexi House Show Home is located on an operational orchard, viewings are by appointment only.
Flexi House is currently offering a free Kickoff Design Package that is designed to get you a floor plan and a price so you can start making decisions about whether a Flexi House is right for you. If you haven’t already, simply fill out our quick Kickoff form and book a time to jump on a call with us. We look forward to hearing about what you want to build and how we can help you into an airtight, well-ventilated, energy-efficient home.
