Ok, since almost everyone here's confused on how to open Ivy's attic, here's how to do it.
I don't think you need to do Dismus and Reynauld's quest (the two guys chilling in the tavern) to unlock the attic. The silver crest is only needed to unlock Erza (the hot demon chick) and Melkor's tomb. I may be wrong here though.
So what you need to do first is to find five hidden notes scattered in your house. Basically, click everything in your house. The notes are mostly hidden in paintings and windows. The first four notes are obtainable at the start of the game and the last one is in Ivy's room (her window, if I'm sure).
With all five notes unlocked, go to your inventory and look through the notes. Each note will have a different symbol. These same symbols are on the grandfather clock in your room. Place the hand of the clock on the symbols one by one in the order given in the notes. Note 1-5 symbol first, note 2-5 symbol next, and so on. After you complete the puzzle, you get a key. I'm pretty sure you know what you need to do next.
Also, if you haven't unlocked Ivy's room yet. Just progress through her storyline. I don't know if it unlocks automatically because it was after I paid Naamu (the almighty dragon that has made himself comfortable on a rock near the lake) 25G for a tip (to finish the achievement) that I found out that her room was unlocked. So I don't know if Naamu triggered it or not. Probably not, cause he's just supposed to be a support NPC.
Now as my reward, I'd rather appreciate it if someone would be kind enough to help me with unlocking Erza third sex scene. That's the only scene I have yet to unlock in v23.1. I have tried both Naamu and the Wiki page, but still no luck, godammit!