by Denise Henkenhaf, eZED Ltd | 8 July 2014
It was a great privilege to conduct the airtightness test for the first Certified Passive House in New Zealand. It was officially certified late in 2012 by the Passivhaus Institut in Germany. The test results were well under the airtightness requirements for Passive House certification at an average of 0.45 air volume changes per hour at 50pa pressure differential. Being New Zealand’s first meant a steep learning curve for the design team.
These very high levels of airtightness were achieved by using an vapour check membrane called Intello®. Particular care is required around services penetrations through the membrane, these were kept to a minimum on this project by using a 45mm service cavity to the interior face of the timber stud framing. The membrane is installed as one complete continual uninterrupted layer to the exterior walls and ceiling. It is fitted and sealed around all the windows and doors with any unavoidable penetrations sealed tight using proprietary tapes, sealant or grommets. This construction method sounds complicated but is in fact quite simple being adopted in 100′s of homes in New Zealand that are not necessarily Certified Passive Houses.
The windows must also be very airtight to meet the Passive House requirements, a standard New Zealand window would unlikely meet these requirements unless it was installed with particular care together with some additional sealing and taping around the frame. The windows on this Passive House were imported European timber frames. It was surprising to see how well the large stacking slider doors performed as these are often avoided in the average Passive House, in this case the window suppliers, EcoWindows, had a determined attitude to make it work and their efforts were well rewarded in the end.
Another potential air leakage point can be the mechanical ventilation system. We see that most ducted heating or ventilation systems installed in New Zealand suffer from significant air leakage. This can reduce the efficiency of the system to a staggering degree. A Passive House ventilation system must meet the same strict airtightness requirement as the house envelope so it must be fully commissioned at the time of blower door testing. With very high levels of airtightness a ventilation system will operate very effectively, taking a minimum amount of time to refresh the air without having the discomfort of noise and high air speeds.
An interesting feature of this house is the gas fire. Although it is pretty unlikely that the heater would ever need to be used in this house, it does offer the home owner a focal point and a sense of comfort in mid winter. The fire is completely sealed, drawing air from a direct outdoor air feed and it fully vents all exhaust fumes. This fire place unit did not have any detrimental effects on the airtightness of the building.
A Certified Passive House blower door test is so sensitive that we have to ensure that all drain traps are filled with a column of water. Air leakage can even register through an old fashioned keyhole.
Get in touch with me if you are interested in having a blower door test for your building.
Copyright eZED Ltd 2014