From PsyHelp
You can expand your house beyond the basic Common Room and Storage with a number of different add-ons, each with different functions and properties.
Add-ons and their Properties
- Airship Mooring
- Used to build an Airship for PvP
- Access to the Aeronautical Society
- Apiary
- Feed bees every two hours to harvest certain items
- A level 5 Apiary will award you with a badge
- Attic
- Adds 20 spaces to your Storage
- Has a locked chest with various goodies (and not-very-good-ies)
- Basement
- Holds 100 items regardless of item size
- Wipes all comments on items
- Expand 100 units by trading in Deeds to 1000 Units
- Colossus
- Reduces Storage fees by 10%
- Grants you a badge
- Dungeon
- Showcase defeated Monsters
- Has mysterious door that can be unlocked in December for items
- Eiffel Tower
- Gives out wine and fireworks on Bastille day
- Fireplace
- Keep a fire burning for various gifts
- Gives a fireplace mantle to display items on users profile
- Grants two badges: one for keeping the fire burning for 500 hours and one for 1000 hours
- Forge
- Smelt and de-smelt certain metals and alloys.
- Greenhouse
- Grow stuff
- Indoor Swimming Pool
- Host Swimming Race events
- Lake
- Add Rubber Ducks, Boats, and a Lake Monster
- Nivaine's Ring
- Bathtime Badge
- Library
- Reduces maximum house size by 100 in return for unlimited storage for books
- Access to the Batcave
- Map Room
- Keeps track of the areas your pet has explored as a Gatherer
- Menagerie
- Moat
- Provides safety
- Fish for things
- Refreshing Spring
- Half-hourly action
- Profile Title Choices
- Shrine
- Light Candles to cause effects and cast spells
- Smokehouse
- Cure Steak into Jerky and Spicy Jerky
- Tower
- Have your Flying Monkey fetch (mostly) alchemical things
- Transmute things
- Windmill
- Wishing Well
- Gain access to the Mysterious Shop and other things.