As interest rate is lower and take home pay as a % of income is higher (lower taxes) compared to other industrial world, it can have a higher than normal HousePricetoIncome ratio and yet a servicing cost as a % of income that is lower.

So, to determine whether HDB value are overcalued, 3 questions needs to be answered:-
(a) Is this subzero interest rates sunstainable?
(b) Can income tax remains at this level?
(c) Can the wage growth trend before the financial crisis sustained..