When making housing decisions, a household faces an uncertain future in a variety of exogenous variables. This uncertainty may cause the realization of the household's optimal decisions to differ from expected (or planned) behavior. The household's decisions are contingent on the probability distributions of the uncertain (stochastic) variables. This study considers the effects of uncertainty in family structure and an unexpected change in the number of family members on the length of stay, housing consumption and tenure choice, which depend on the nature of uncertainty, degree of the shock and financial constraint such as transaction costs. One implication from the model is that the uncertain family size is transmitted to the household's lifetime budget constraint by changing personal exemptions, after- tax income and tenure choice (or marginal) tin rate, resulting in uncertain lifetime after- tax income and user cost of owning. Depending on initial assumptions of exogenous parameters, simulation results reveal different results due to complex interactions of income and substitution of effects.