Roof ventilation isn’t required. But we design it anyway.
Five years ago, roof ventilation wasn't something we routinely built into a design. Today it's close to standard practice in our office. Nothing in the Building Code forced that shift, the rules covering roof space moisture read the same now as they did back then. What changed was everything around them.
A string of moisture-related failures across the industry put roof spaces under scrutiny they hadn’t faced before. Trapped moisture, mould, damaged framing, problems that often traced back to a roof space with nowhere for air to move. As those cases added up, awareness spread through the trade.
BRANZ has been publishing guidance on the topic for a while now, covering when ventilation matters most and how to design it well. The New Zealand Metal Roofing Manufacturers group has its own guidance too, setting out the ventilation pathways a roof needs to manage moisture properly. None of it is a legal requirement. It’s become recognised good practice, and the trade has largely got behind it on its own.
The clearest sign of that shift is where the money’s going. Developers and housing groups don’t have to spend on roof ventilation. Increasingly, they’re choosing to anyway. That’s usually the real marker that something’s moved from a nice-to-have to how a job gets done properly.
It’s why roof ventilation has become a standard part of how we detail a roof now, not because a regulation requires it, but because the industry worked out, the hard way, that it’s worth getting right from the start.
