Size matters, but that's not all

I am considering moving in with 3 to 5 Brazilians next semester. If all 5 and I decide to live in a 4 bedroom house, that means 4 people will be sharing 2 rooms and 2 people will have their own. Let us say all the rooms are of equal size. How do you split up the costs?

A simple answer may be to have each room cost 1/4 of the rent. In this scheme, a room splitter pays 1/8 of the rent, while a single pays 1/4. (For a $1500 house this is $187.50 for a splitter and $375 for a single).

But a house is not only rooms. There is the kitchen, living room, bathrooms, storage space, lawn, etc. So the question is, how much is all that stuff worth? If we decide that 50% of the value of the house is in the rooms, then the rest is valued at 50% of the total rent. Example:

We go in on a $1500/month house. Let us give value of rooms to value of rest of house a 50/50 ratio. Now each inhabitant pays ($1500*50%)/6 people = $125, solely to live in the house. But of course you want to live in a room right!? Well the marginal (or extra) value of adding a room is ($1500*50%)/4 rooms = $187.50 per room. Under this scheme a room splitter pays $218 and a non-splitter pays $312.50.

The driving metric is the ratio of the value of the rooms to the value of the rest of the house! A room splitter argues that the rooms are very valueable and should not have to pay much for just living in the house. Whereas a single roomer, which I will be, argues that rooms aren't that important and it is really the whole house that we are splitting.

Perhaps it seems interesting that the people deciding to have a roommate think (or at least say!) that room space is so important, while those having their own room think that room space doesn't matter so much; they should switch! The falacy here is that all room space is equally important. If I have a big room to myself and you take away one square foot, I might not even notice. Do the same thing in a small room I am sharing with some one else and I will surely notice! I value the square foot much more when I have only a few to start.