“Cold, damp & draughty” could be a few words to explain a 1920’s house but guess what, those exact same adjectives can be used to describe most new builds in New Zealand in the 2023. In last week’s article “Why the NZ H1 Building Code Change Fell Short” we touched on the shortfallings of the updated building code changes that caused $20–40k of cost increases for new builds by making changes to things in all the wrong areas but not addressing some of the key fundamentals. In this article we will cover what should have been put into place to make our houses healthier to live in.
If you build a brand new home today and follow the building code I wouldn’t be at all surprised if you still got condensation on your windows and mould throughout your house. I’ve seen it in new homes where there is mould on the back of furniture, behind curtains and in bathrooms and condensation not only in the bathrooms but in the bedrooms in the mornings. No wonder New Zealand has some of the highest asthma rates in the world, we live in airborne pathogen petri dishes for houses. Kiwis are so cavalier when it comes to mould, we think we can live with it or simply clean it away when it builds up too much. In America, they understand the dangers of mould and treat it like asbestos because they know what a mould spore can do to your health. You wouldn’t expose your children to asbestos so why do it with mould?
If you like cold and draughty homes; go ahead and build to the NZ building code but if you want a healthy home, with healthy occupants, that will be cheaper to operate than you should continue reading.
So when building better houses we need to improve on some aspects of construction and it’s best to look overseas to prove what is working. Idealy the best practace would be if every house is a certified Passive House but it will take quite some time to get there but lets take a few smaller steps first. The changes below would have cost less than the recent code changes that were made but would have had a much greater impact into the health and running cost of houses so maybe we can just put this list towards the next round of changes. If I were in charge of the H1 code changes I would have specified these three things.
Better insulation:
It is hard to correctly insulate wall and ceiling cavities and a lot of insulation under performs because of poor design & poor installation. Gaps of 0–20mm are not uncommon and a small 20mm gap between the wall and insulation can turn an R2.0 wall into an R1.3 wall. We should implement what California has been doing for over a decade & that is external insulation. In California all houses have to have a continuous layer of external insulation on the outside of the framing of the house, often this is a rigid insulation that is attached to an OSB or Plywood. This gives the house an uninterrupted layer of insulation that outperformed a cavity insulation. In most cases they do a mix of both external & cavity insulation. It has the added benefit of stopping air leakages into the framing.
Air Tightness:
If you can control the drafts in the house you can control a lot of the heat loss to the house. Think about where wind gets in and what it does to your house, it blows dirty cold air into your house and settles dust & pollen throughout. The drafts even get into the external walls and push around the insulation sucking heat away and sometimes it comes in through the strangest places like the power points & light switches. The door between the house and garage are often a big point of failure, as well as sliding external doors and most front doors. Adding an air tightness approach to the house is quite simple, some times it is as simple as using tapes on RABs and making sure the wall to slab is sealed as well as the ceiling and roof have been properly thought about. It’s quite simple to make a house more air tight, it’s even more simple to do a blower door test to check the performance.
MVHR:
Now that you have insulated the house better and eliminated the drafts it is time to consider how to control the air in the house. We are not talking about a positive pressure system from a local company that has 3 letters in their name, we are talking about a Mechanical Ventilation Heat Recovery unit. In a car filled with people if you have the air on circulate for to long it will get stuffy and houses are the same but this is where an MVHR is worth it’s weight in gold. An MVHR will take all the moist stale air out of the house and replace it with fresh dry filtered air but with one key difference, it passes over a heat exchanger before replacing the air. These units are often up to 95% efficient meaning even in winter when it’s 2 degrees outside the air you bring back into the house is likely to be 18 degrees. MVHR’s are very cheap to run because simply put they have two constant fans that simply blow over a heat exchanger.
I think the largest reason why the codes are not improving is because of the push back from the building industry itself, most builders don’t like change and they want to keep building houses the same way that they have always done. If we needed to bring in air tightness and external insulation it would be a change to the detail & design as well as require more education. These 3 changes would have cost about the same as the changes that were enforced this year but would have had a much better return on the standard of living and the running cost of the house. New Zealand has always been behind the eightball when it comes to the healthy standards and energy efficiencies of building codes. We are very quick to change things if someone’s life is in immanent danger but what about things that are slowly killing us, is it going to take another 15 years before we see blower door testing mandated?
