unheard

Gable vents are super common in Thailand. Yet there're hardly any vented ridges. The local builders have never heard of those. At least not on the residential roofs.

No, those are soffit intakes. The do allow some outside air in but don't create much of a circulation on their own. A little bit of air movement that they do provide is close to useless unless there's an opening big enough somewhere higher in the attic to allow the hot air to escape, e.g. gable vents (good) or a ridge vent (best).

I think that's very close to an ideal combination - metal roof with the attached PU foam underneath plus fiberglass batts above the ceiling. An addition of ventilated roof ridge would make it ideal.

That type of a metal roof should be leak-free for decades, if properly installed. What kind of a metal roof do you have in mind?

Sorry, haven't seen that one... What kind of a metal roof? The foil is not an insulator, it's a radiant barrier. 2 in. of PU insulation underneath would truly make a real difference in the amount of heat transferred through the roof.

Non-insulated metal roof?

Drilling is always an option, rock or not. They will drill through solid rock, no problem (with a right equipment). The only problem is the added cost of the capable contractor and his equipment.

https://www.testtech.co.th/public/th

Again, it's another marketing video, nicely produced I should add. I'm sure there are many more similar videos out there. Those videos never provide any evidence or anything of scientific value to back up their claims.

Viva Marketing!

Physics is so last century... Marketing Rules!

"A good advertorial explains this well." And advertorial "explaining" things?

I'd think Bagwain would know how to share his knowledge here without triggering any trouble. The OP has brought up a very good question. I think the rest of us would be interested to learn Bagwain's response.

or cost-effective

Zero chlorine in the water? No doubt that UV and ozone systems sound quite sexy and "advanced" but... They're not considered to be the safest...

Failed control units or worn down titanium cells which are replaceable?

Not only the steel roof structure, but also the tiles experience the same daily contraction/expansion cycle. The main reason for why tile roofs require periodic inspections for any cracked or moved out of position tiles.

Metal sheets with an attached 25mm (or thicker) polyurethane PU insulation are not as noisy as you think. And if you're ok with the looks, will provide a better option for a leak-proof roof.

Tiles undergo a daily expansion-contraction cycle, more so in the dry season and if located on the side facing south. Depending on quality of the material, some tiles are more resistant to cracking than others. Quality of installation can also play a significant role in cracking.

"So my house is now 16 years old and the roof tiles have started cracking. Got a contractor that's due to paint the roof (clean, prime, 2 top coats) and claims this will fix the problem for 5-10 years. Anyone out there that's been through this and has any advise to share?" Painting is purely cosmetic and will not fix the cracking problem. If you have a widespread cracking problem then your particular tiles are nearing the end of their useful life. It's time to plan for a new roof.

"Intention is to get to a stage whereby a draughtsman should be able to follow and create an official set of plans." If that is your main intention then I would agree with gamb00ler - Sweet Home 3D is a free, relatively simple to use application. With lots of tutorials and the active user support forum. I've used it to create different plans to play with various design ideas. Once settled I sent snapshots to my architect which had no problem transferring the design into the engineering drawing.

Totally disagree on the statement that "ridge vents are static and won't move air the same way turbines do." Yes, ridge vents are static as no moving parts involved (first advantage), but they will also move an enormous amount of air by volume as compared to turbine vents. (second big advantage). You can simply compare the dimensions of the opening provided by the whirlybird against the opening provided by the full length of vented ridge.

That's all great that you're satisfied with their "performance." The point being made here is that for anyone else who's just considering installing whirlybirds - go online and research the subject for yourself in order to make an informed decision. There's aplenty of available material online.

Probably won't make much of a difference - the air volume in the attic will remain stagnant. Should only make some difference (maybe) on windy days. What you really need is to try to create conditions for a constant air flow. Hard to achieve without a higher roof and a vented ridge(s). Even on a low pitch roof a vented ridge still could make a significant difference - the hotter, lighter air would want to move to the highest point of the structure (ridge) and escape if there's an opening, if not then it will just seat there, gradually gaining temperature.

If you remove the whirlybirds and just leave the holes open (with some rain covers), the airflow would stay exactly the same.