Why would the OP somehow think this would increase sales of their products?
In any case, the answer is very, very badly.
Still as yet to see an asphalt shingle roof installed correctly in Chile. I did a tour of duty as a roofing contractor while in my first years at the University. Every single one I have seen installed in Chile would have been a law suit back in the States, and definitely no warrenty. The worse thing is they are getting popular now. So, the number of badly installed asphalt roofs is going up dramatically.
Let's see, top on my no, no list:
No roof vents of any sort. No soffit vents. No ridge vents. no vents. asphalt roofs need to breath from the underside, or the decking rots away. The nearest thing to a vent, is all the leaks in the rest of the building envelope of the house. They sell roll out ridge vents in chile, but it is really frigen expensive. No one knows what to do with it anyway. How to calculate the air flow needed, and so on.
Using tyvek under the shingles. Which, perhaps you could get away with, except they don't know how to use tyvek either. Seen a house down the road that that had about 40% of the roof covered in tyvek, part builders felt, and part nothing, all shingled over. I noticed they ripped the tyvek off and put it back on several times (I am sure ripping holes in it, and never seen the stuff taped) as they tried to figure out how to use it.
Roofing nails were almost none existent 4-5 years ago in Chile. Now they do sell them fairly commonly. However, I still see a lot of guys using regular, without galvanization, type nails on asphalt shingles. The heads are too small to keep the shingles from ripping off. The maestros do not make the connection between those stubby big headed nails and the asphalt tiles being sold on the other side of the home center.
Flashing. drip edges. never mind.
Roofing tar, for covering up those nail heads, sealing whatever hole they ripped in whatever, not in use.
Tar paper (if used) that is way light for a roof, and not lapped correctly, has tears in it, and so on.
All of the above, typically put on roofs with way, way to low a pitch (1:12 or 2:12 anyone?) especially considering what is under the tiles is not water tight.
Ow, almost forgot. The osb roof decking is too thin to start, sometimes spread as much as 48 oc, often over 2x6 studs that are spanning incredible distances. They would have made those undersized rafters go even further, if they could have found a 2x6 that was longer. Luckily about 4.0 meters is as far as they could find at the local saw mill. It gives the entire house a nice seasick sensation when the wind blows, and you won't even notice the difference when an earthquake hit because the wind moves the building like an 9.0 all the time. No one explained to them that asphalt roofs are heavier than the typical Chilean metal roofs.
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