If you use a traditional roof construction in New Zealand as per NZS3604 this year, you are wasting planetary resources, wasting your hard earned money and opening yourself up to a potential leaking roof. A bold statement, but unfortunately very true!
For years in New Zealand the “gold standard” was a concrete tile roof. We have all heard if we all built “brick and tile” the world would be a better place. However what they don’t tell you is the amount of extra structure (cost/resources) and bracing (cost/resources) you have to build into that same house to hold the enormous roof weight of concrete tiles. Also you have to control that same enormous weight in an earthquake. If you want to see how they perform in an earthquake, just ask the Cantabrian’s how their concrete roof tiles fared on their roofs through the quakes of Christchurch as of late, most ending up in the house or on the ground beside the house.
Then there is the “water-tightness” issue, yes a glazed concrete tile is water resistant when new at the factory and maybe even when it arrives on site if handled correctly. However when it is installed on a roof or some hairy walks across the roof, cracking a tile when installing the sky dish, the water resistance is gone! Water is then flowing you’re your house and you can see the damage to the tile only the resultant damage to the house. When the tiles age and the coated surface breaks down, they absorb water through the top, transferring it through the porous concrete tile to the interior of the building roof structure. Now some wise person who makes rules said, “That if the roof is over 17 degrees in pitch, you do not need to use a roof underlay” And so thousands of NZ house have followed this mantra. Think about it, there are two main reasons that this is flawed thinking. One if they are cracked or weathered the water falls directly onto the roof/ceiling structure and the insulation (assumes it has some). Then the second issue, all water vapour created within the building envelope (showers/cooking/steam etc) rises up permeating through the ceiling and insulation until this warm vapour meets the cold concrete tile, then what happens, it condenses and falls down onto the structure/insulation creating the same issues as if it was leaking.
The perfect roof is one that comes with the biggest warranty, the best water-tightness and the cheapest price to the end user.
Before you make any further decisions, look up structural insulated panel roofs.
Light weight (standard structure) impervious (water tight) cost effective (on average 50% cheaper) and 50 year durability warranty (45 years more than code) in New Zealand. Yes you are limited to simple roof shapes, but why would you want to build complexity into a waterproof system?
Till next time……………………Art for living! G