My wife and I worked out on paper the basic dimensions of the house, position on the block, drafts of the facades and floor plans. We then sought help from a very experienced architect, who was new to passive house. Here are some of the elements that I should have thought about in more detail.
Heat Recovery Ventilation System
Ours is located in a cupboard in the kitchen. This was done in an attempt to isolate as much noise as possible in the kitchen, which has worked. What we should have been thinking about at the same time was how to create space for the ducting to run through the frame and where it would rise through the first floor to the ceiling. Ultimately, we were able to use a bulkhead and a lowered kitchen ceiling to spread ducting and other services horizontally and a section of 2 built in wardrobes for vertical spread.
Bushfire Smoke
With the frequency and ferocity of bushfires in Australia, I should have enquired more seriously about ways to add a HEPA filter to the system for short-term use. I believe that retrofitting one now would be difficult with our Zehnder unit because it was installed in a tight space and there is no built-in way of dealing with any change to the flow rates that a HEPA might create.
On the positive side, because the ingress of air into the house is so well controlled, we should have success with a good quality residential air purifier.
Ceiling Fans
This one really is a beginner's error. Because our BASIX commitment was for 1 ceiling fan, I saw an opportunity to save some money and use the HRV to move air around the house. In summer, we pretty quickly realised that the air moves too slowly to compensate for the heat that was sitting in the relatively warmer parts of the house. We have since installed fans in all bedrooms and a downstairs office. With very limited access to the ceiling void on the low side of the skillion roof, this required cutting into the ceiling gyprock to install timbers and run wires. Quite the opposite of a saving.
Mechanical Noise in the Ceiling
The ceiling void is within the airtightness layer and the insulation is against the rafters, unlike in many standard homes where it sits on the gyprock of the ceiling between the joists. Our roof is a 5º skillion with about 1 metre of vertical space on the highest side, meaning that it is a pretty compact space. The indoor fan coil unit of the ducted air-conditioning system and ducted de-humidifier sit on the joists in that space and send vibrations into the frame. Because the ceiling is airtight, there are fewer places for the noise of each to escape through the roof. Low frequency noise comes through the frame and higher frequency noise moves in the air back into the living space. This is audible because a passive house is much quieter than a standard house when the windows are closed. To try to combat this, we put 13mm gyprock on the ceiling, which may have made a difference, but I suspect we should have thought about better isolation between the mechanical units and the frame.
Fixings in Timber Cladding
I regret not thinking about how the fixings in the timber cladding would appear after painting. Major regret.
Dehumidification
This became a bit tricky in our case. It is worthwhile focussing on this area with your PH consultant. We ended up with a ducted dehumidifer, which we rarely use for general dehumidification, but which is very good at quickly de-fogging the bathroom mirror after a shower.
Heavy Doors and Lightweight Frames
All the exterior doors are hinged. They are timber with an aluminium veneer, double glazing and quite a bit of steel, locking componentry, which is a good thing. This means that they are heavier than most standard Australian doors and cause the frame to bounce slightly when being closed. The movement has caused a superficial crack in the junction between the door frame and architrave, that will need to be siliconed when we paint the house next time. It is definitely something to keep in mind if you are considering a lightweight frame and timber cladding.
Window Restrictors and Night Purging
If night-purging warm air is part of your PHPP, be aware that widely opening upstairs windows will be made difficult by window safety legislation in NSW. Definitely have a read of the requirements before you sit down with a designer. We used doors that open onto a balcony to get large openings.
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