The Best Kings Wear Skirts

[Bugs]

Lost the recipe and couldn't be bothered to find it?

Click to shrink...

Unfortunately, that tracks with schools' general attitude towards maintenance in general in my experience.

 

[Wyrd]

According to my own headcanon, Hogwarts is cold and draft is because it was originally coated with the same type of plaster as every other castle at that time period was coated with.

The plaster kept out drafts, protected the stone and mortar from the weather, hid imperfections (weaknesses) from enemies, and made the castles look nicer.

However, the plaster wasn't 100% waterproof, and needed to be regularly re-applied.

The lack of re-plastering is why abandoned muggle castles appear to be made of stone.

When the Statute of Secrecy was signed, Hogwart's plaster was removed, and muggle-repelling charms attached to the bare stone walls, magically amplifying the appearance of the bare stone, preventing any muggle from noticing anything other than the castle's stony-ness.

Why the inside doesn't have insulating / draft-blocking plaster... I'm not sure. Over-enthusiastic cleaning charms?

Click to shrink...

The problem is that they don't understand the science of thermodynamics. They put warming charms on the walls instead of plaster on the walls, when what they should be doing is, A, properly insulating the place, and, B, putting the charms on the floors. Put cooling charms on the ceiling, and you have a climate controlled castle. Then again, with how long wizards live and a culture that resembles a geritocracy(rule by the old), so school board members have, most likely, repeatedly insisted that, "if it was good enough for me, it's good enough for them!" and, "A little cold is good for them! Don't want the next generation to grow up to be spineless wimps!"