Specifying UPVC windows for a low-rise home and specifying them for the 25th floor of a residential tower are not the same exercise, even though the product family looks identical on a brochure. Wind pressure increases with height, water and air tightness requirements get more demanding, structural movement in the building itself has to be accommodated at the window opening, and a hardware or seal failure that's a minor inconvenience at ground level becomes a genuine safety issue several floors up.