Here is a spreadsheet analysis that I did a while ago, updated with latest avail figures. Blue cells are variables, and everything else feeds off that. It illustrates what happens to "affordability" over 20 years with varying property price growth rates, and what happens if sustained growth rates are unrealistically high.
From what I have been able to discern, acceptable Mortgage Repayment Ratios vary between 30% and 40% of Gross Income. This table compares MEDIAN HOUSEHOLD DISPOSBLE INCOME.
Ave World Wide Price/Income ratios differ depending on what source you read, but it seems that anything over 4 times is regarded as unsustainable/expensive.
