Keady Street
Building Efficiency Goals – achieving airtightness in a weatherboard renovation
The Keady St renovation is an extension to an old weatherboard home in Northern Melbourne. The brief was to expand the house at the rear, giving more living space towards the garden and updating kitchen and utility areas. The clients primarily wanted to achieve a comfortable, healthy and energy efficient home. Our mission was to achieve the highest standard of efficiency possible, within a modest budget and retaining/ working around the original structure.
The original hardwood framework after existing cladding had been removed.
Extending the footprint.
LOW ENERGY comfort PART 1 - Airtightness
Cross section of exterior walls. The big difference when compared to traditional construction is the vapour permeable membrane and the ventilation layer outside it. This allows moisture to escape the building rather than remain trapped where it risks rotting the timber framework and rusting metal fixings.
Our goal: to make the building envelope almost completely airtight. In short, the rationale behind this is to allow control over the flow of air into and out of the building, thereby controlling heat, humidity, and air circulation.
Reusing the original framework made for quite a bit of improvisation in the build to ensure that the integrity of the envelope could be maintained from the new section, into and throughout the old part of the house.
We used premium building wrap breathable membranes to completely enclose the house in an ‘envelope’.
Our team squeezed into tight spaces to achieve complete coverage!
All walls, floor areas and ceiling joins are wrapped, making a uniform 'envelope' enclosing the house. Potential gaps, such as where pipes, services extrude, are carefully sealed ... and we worked with our electrical and plumbing trades to minimise disruption to the envelope. Above, the hot and cold water pipes are insulated to stop heat gain and loss.
To prevent future penetrations of the airtight membrane, we provided pre-sealed conduits for solar panels and future car charging power outlet.
LOW ENERGY comfort PART 2 - INSULATION and minimising thermal bridging
As well as being almost airtight, the building envelope features a carefully laid out, gap-free layer of insulation. Careful attention was paid in planning to the design of framework to ensure minimal thermal bridges. A thermal bridge is a ‘heat transfer’ pathway leading to heat loss/ gain through the insulation.
A benefit of using the weatherproof wrap is that the insulation is effectively sealed from dirt and dust. Over time, insulation subject to dust ingress will become less insulating. It’s not just dust that can make its way in; rodents looking for a nice warm home are a common problem too. While the insulation layer is completely sealed behind the weatherproof wrap, the ventilation layer needs air flow. Entry and exit points around the eaves and the bottom of the walls all feature guards to stop anything getting in.
Otherwise efficient buildings are often let down by substandard windows and doors, creating thermal bridges and leading to harmful condensation. In this project we used Passive House-certified suppliers for U-PVC windows with warm edge glazing and double-sealed timber front and rear doors.
Insulation sitting snuggly between the under-floor wrap and the sub-floor.
Insulation installed.
LOW ENERGY comfort PART 3 - Fresh air
With such a high level of airtightness, there is a need for mechanical ventilation to ensure fresh air inside when it is too hot or cold outside to open windows and doors (also when outside air quality is poor – think of Melbourne during Summer 2020).
Keady street is fitted with the Rolls Royce of Heat Recovery Ventilation (HRV) units from Zehnder. Fresh air from outside is run through a G7 filter removing pollens, pollution particles and dust. The unit ensures that the air entering the house is at about the same temperature than the air leaving (relying on effective airtightness for this heat exchange). The unit must be located inside the building envelope, and with a few crafty modifications we hid it away in the roof space of the old house. It is important for the design phase to consider the HRV location for this reason.
‘Nerding out’ on airtightness
The test for airtightness involves fitting a blower door machine to an external door, creating a ‘vacuum’, and then measuring the movement of air to determine the cumulative size of leaks throughout the building. RPB recently became certified with ATTMA as a registered building air tightness tester, building on Ryan’s interest in building physics and efficiency, and certification as a Passive House Tradesperson.
Those familiar with Passive House (PH) (the most stringent airtightness standard currently in Australia), will know that the PH target is 0.6 complete air changes per hour (ACH) at a pressure of 50 Pascals of pressure. For a renovation (retrofit), the PH target is 1.0 ACH. Noting that this build was not aiming for Passive House certification, we nevertheless managed to hit 0.34 ACH.
Great! But what does this result mean?
Our clients can expect a comfortable, well-ventilated environment year-round with minimal heating and cooling throughout Melbourne’s weather extremes. This model of building, including prioritising resources to building wrap, quality windows and doors, and the integrated mechanical HRV, also has benefits for long-term health. While Australian building regulations have progressed to require greater attention to building ‘seals’, without concurrent focus on good ventilation there is an emerging epidemic of health issues caused by mould and condensation build up.
For Ryan Parkes Building, the result is a gratifying validation of our careful attention to building envelope, use of quality materials, windows and doors; and working with trades who understand our aim. Importantly, it demonstrates that high performance homes are entirely possible even for clients working with a modest budget.